Dr Gunnar Kirchhof (Brisbane - AUS)

Complete List of Publications

D Hauswirth, Pham Thi Sen, O Nicetic, F Tivet, LQ Doanh, E Van de Fliert, G Kirchhof, S Boulakia, S Chabierski, O Husson, A Chabanne, J Boyer, P Autfray, P Lienhard, JC Legoupil, ML Stevens, 2012. Conservation agriculture and sustainable upland livelihoods innovations for, with and by farmers to adapt to local and global changes, 3rd International Conference on Conservation Agriculture in Southeast Asia. 10th - 15th December 2012, Hanoi (Vietnam)

Agriculture in whatever age, under whatever natural, economic and social conditions, has to feed the human being. To fulfil this mission, the sector has to overcome continuous and changing challenges to achieve notable developments. The Green Revolution, through developing and introducing high-yielding crop varieties and advanced crop management techniques, saved billions people from starvation. The advent of biotechnology, in its turn, has speed up the agricultural growth to meet food demands of the world's booming population. Continuous demographic pressure and rapid market integration have created necessity to further agricultural developments to meet not only food security, but also the increased demands for nutrition security, food safety, energy, etc., while the global climate change has created needs for capturing synergies between agricultural production and environmental protection. New breakthroughs to trigger the second Green Revolution have therefore become necessary. Thus, it is now the right time for us to consider the means to make "the Double-Green Revolution" to become a reality. Conservation Agriculture (CA) has demonstrated potential to meet this goal through designing and promoting the adoption of environment-sound and climate-resilient agricultural production systems. Increasing interests and efforts have been given to CA research for development in the Southeast Asia during the last 15 years.

Gunnar Kirchhof, Nguyen Hoang Phuong, Trinh Duy Nam, Oleg Nicetic, 2012. Farmer-friendly erosion control measures in maize-based systems of the northern mountainous region of Vietnam , 3rd International Conference on Conservation Agriculture in Southeast Asia. 10th - 15th December 2012, Hanoi (Vietnam)

We evaluated soil erosion rates in farmers’ field to assess when erosion occurs during the maize season and to identify which soil management aspects have the most profound impact on soil erosion reduction. We used a modified profile meter method to monitor erosion in farmers field (Hudson, 1993). Unlike Wischmeier plots, this method has minimum impact on farm operations. In short, this method monitors the drop in soil surface level below fixed reference point. These reference points are steel pegs (pins) inserted in the soil and distance between top of pin and soil surface measured following rainfall event. Our pin method comprised 4 soil pins inserted into the ground to ~40 cm in a 70x100 cm rectangle and we monitored soil surface to pin distance at 8 constant locations within this erosion station. Measurement errors using this method can be large due to slumping of soils after tillage and soil swelling. We compensated for these shortcomings by taking a large number of measurements, monitoring of soil bulk density to account for slumping of soil and assumed shrink-swell was negligible on these 1:1 type clay soils. Although slumping occurred, it happened very quickly after tillage following rainfall and once the maize was sown, slumping was no longer observed; i.e. there was no measurable change in surface bulk density after maize was sown. The research comprised of two phases: (i) collection of baseline date on erosion in farmers field and (ii) to monitor soil erosion in field experiments at two Communes, Na Ot (Son La) and La Nga (Moc Chau). The field trials (ii) was a complete randomized design using 4 blocks. Each plot had two erosion monitoring stations and erosion was measured 8 times during the maize season in Na Ot and 10 times in La Nga. Slopes were ~25º. Other key measurements were rainfall intensities, final maize yields, bulk densities and infiltration rates (i.e. single ring). Following discussion with farmers, treatments were adjusted to what farmers though they may use in future. Cultivation at both sites was done using a hand hoe. At La Nga the treatments were (i) cultivation residue retained plus additional mulch added, (ii) cultivation and residue retained, (iii) minimum cultivation with residue retained and (iv) cultivation with residue retained and rice-bean intercrop, i.e. all treatment had residue retained and no burning took place. The amount of residue from the past crop ranged from 1 to 3 t/ha, the additional residue applied ranged from 3 to 5 t/ha. At Na Ot the treatments were (i) slash and burn, (ii) residue retained and cultivation, (iii) residue retained and mini-terraces and (iv) residue retained and minimum cultivation; i.e. all treatment except treatment (i) had residue retained. Average residue amount left from the last season was 4.3 t/ha with an average groundcover of 83% before land preparation. The difference in residue amounts between the two sites is due to grazing during the dry season. For the benchmark study (phase i), erosion was monitored in farmer fields of 5 villages from End-July to mid-October at 5 different times. These villages were located in different communes in 4 provinces (Mai S?n, Moc Chau, Sin Ho, Tam ???ng). Erosion stations were located within farmers’ fields on slopes between 20º and 30º on slope lengths larger than 100 m. Distribution of the 68 erosion station was uneven between farmers’ fields as it depended on access and farmer support to allow measurement. Average soil loss ranged from 8 to 15 t/ha during that time and there were no significant differences between provinces, communes and farmer fields. We attributed these low erosion rates due the late onset of the monitoring schedule; i.e. maize was well established providing effective erosion protection through reducing raindrop impact. Given obvious visual assessment of erosion, we concluded that most erosion occurs during the early phase of the growing season while the soil is unprotected. During the 2011 maize season average erosion at La Nga was 38 t/ha, with a very large variation from 3 to 95 t/ha, but no significant differences between treatment and it was not possible to differentiate between erosion rates at the start and towards the end of the maize season. We attributed the lack of significant differences to the similarity of treatments where all treatments had residue retained as well as the inherent variability of the erosion method we used. At Na Ot total erosion rates were much higher compared to La Nga and segmental regression of erosion rates showed that there was a significant difference between the start and the end of the maize season. Most erosion occurred until the 7 July 2011 (initial soil loss). The first erosion measurement was done on the 22 April and maize sown on the 11 May. This suggests that a large proportion of soil lost during the initial phase occurs after land preparation and before the maize is planted and aggravated by weeding (Podwojewski et al. 2008). Initial soil loss was 226 t/ha for treatment (i), i.e. slashes and burn. There were no significant differences between the other treatments where residue was maintained and average initial soil loss was 101 t/ha. The difference between residue burnt and residue maintained was significant at the 5% level. The average soil loss rates after the 7 July 2011 was 17 t/ha with a range of 5 – 25 t/ha and no significant differences between treatments. The results of our research showed that most soil erosion occurs within the first 2 months of the cropping season and the main factor in reducing erosion is maintaining ground cover. The importance of this finding is that practice to reduce erosion is to encourage farmers not to burn and to maintain crop residue.

Neal Menzies, Andrew Verrell, Gunnar Kirchhof, 2012, Keynote 5: Can conservation farming practices ensure agricultural ecosystem stability?, 3rd International Conference on Conservation Agriculture in Southeast Asia. 10th - 15th December 2012, Hanoi (Vietnam)

Conservation Agriculture is deemed to be the only sustainable form of agricultural production system. Adoption rates in the Americas and Australia have been extremely high associated with increased and more efficient crop production, but primarily due to the reduction of herbicide cost, mainly Glyphosate, after patents expired and competition for production increased, lowering the cost of Glyphosate. Conservation agriculture is a production system where a key component isherbicide use to replace tillage in the control of weeds. Other equally important components are mechanisation, and residue retention; associated with crop rotation to reduce the likelihood of pest and disease outbreaks. Practitioners of conservation agriculture universally understand that that all components must be applied; partial adoption of the conservation agriculture principles will not be sustainable. In regions where conservation agriculture has been adopted as a system, at present, it is the best management practise for agricultural ecosystem sustainability. However, in many developing countries, practise change for all components of conservation agriculture may not be possible. Herbicide availability and cost is probably a major limiting factor; in particular, in many sub-Saharan counties. The need for agricultural mechanisation at present still limits the adoption in many African and Asian countries. Crop rotation may not fit into traditional production systems and minimum tillage is not possible to implement for root or tuber crops. Similarly, genetically modified cotton production requires tillage for pest control. Soil and climate interactions may also hinder adoption of the minimum tillage component. Some soils, for example heavy self-mulching Vertisols respond very well to the conversion from conventional to zero-tillage and benefits in terms of increased water use efficiency are evident shortly after aggressive tillage operations ended. However, less active soils, in particular hardsetting soils, may not respond rapidly to zero tillage, and it may take several years of zero-tillage practise before soil structure has sufficiently improved for conservation farming to outperform conventional practices. In Australia, profound nutrient stratification (accumulation in the surface soil) also presents a challenge to zero tillage. At present is seems that conservation agriculture is promoted as a ‘must adopt’ as a system where, at present, this may clearly not be possible in some biophysical/socio-economic environments. The change to conservation agriculture needs to be stepwise process where adoptable components are promoted and associated limitations are addressed without short term yield sacrifice. Key indicators for the agro-ecosystem stability of conservation agriculture are soil organic matter build-up and carbon sequestration due to minimum soil disturbance and residue retention and increased water use efficiency. Increases in the soil organic carbon stocks are largely reported on conservation agriculture fields in the Americas. Research in Brazil suggests that organic matter build-up under conservation agriculture can even be greater than under natural ecosystems. Results from the USA suggest that soil organic matter build-up is a major mechanisation for carbon sequestration. On Vertisols in Australia adoption of conservation farming was partly due to the realisation that carbon stock depletion needs to be arrested, and the belief that soil organic matter can be increased in conservation agriculture systems. However, despite soil structural improvement due to adoption of zero-tillage systems, recent data from longditudinal studies shows that carbon stocks have continued to decrease under conservation tillage, though at a lower rate than observed in conventional tillage. For example, on farmers field were conservation agriculture has been practised for over two decades, no increase in soil organic carbon was measured. Unless annual rainfall is above 500 mm, increase in soil organic matter as a consequence of conservation farming practises appear to be negligible. If these values also apply to soils and climates in Africa, large regions of Africa need to be excluded as potential carbon sinks. Minimum tillage systems, once soil structure has improved, even in the absence of organic matter increases, will have increased water use efficiency. This is primarily due to the greater amount of actual available water but not necessarily due to an increase in potential plan available water. The main mechanism for high amounts of plant available water in the soil profile and associated higher water use efficiencies is greater infiltration rates that allow the soil profile to fill out with water. Benefits for crops are obvious but there may be a hidden cost for environmental flows. Higher water use efficiency is synonymous to lower losses in the water balance may well lead to reduced water availability downstream from regions were conservation agriculture is practises. The potential impact on landscape hydrology are largely unknown.

Kirchhof G, So HB, Tuong TP (2011). Puddling: Effect on Soil Physical Properties and Crops. In: Encyclopedia of Agrophysics, Springer Reference, Gli?ski, Jan; Horabik, Józef; Lipiec, Jerzy (Eds.). 1st Edition., 2011, p667-8.

Soil puddling for paddy rice production is the process of working saturated or near-saturated soil into soft structureless mud. Tillage in lowland rice production systems (paddy rice) is synonymous with puddling. Puddling is achieved by cultivating the soil under saturated condition using animal drawn or tractor driven implements. Mechanical breaking and dispersing of soil aggregates destroys the soil structure and forms the puddled zone. Puddling softens the soil and assists manual transplantation of rice seedling, minimizes water use through reduced percolation losses and effective weed control. Over time, soil puddling also creates a compacted layer below the puddled zone which further reduces percolation losses. The least permeable zone is usually found just below the puddled layer where tillage implements created a thin smeared layer. The reduction in permeability is mainly caused by blocking of macropores with fine dispersed particles translocated during puddling process, and the smearing effect of the tillage implements. Although lowland rice does not require saturated conditions to produce high yields, it is traditionally kept under submerged conditions to maximize water supply, mobilize nutrients, and to control weeds, which is generally not possible without puddling. However, preferential flow or bypass flow through macropores, cracks, or large biopores contributes to water losses in paddy systems. This includes water losses though bunds which are not puddled. Water moves laterally into the bunds and then percolates down through the under-bund areas that are not puddled. Despite the benefits of puddling for rice production, there are adverse effects, especially on post-rice crop production. Due to its structureless nature, puddled soils tends to harden and crack upon drying, with the rate and size of crack development depending on the rate of drying, type of clay, and clay content. These characteristics are the main constraint to the establishment and growth of post-rice crops. Irrigation of dried paddy soils can result in excessive losses from bypass flow, while severe cracking can result in root breakage and excessive strength impedes root growth. Although soil puddling reduces the percolation rates, the puddling process itself requires large amounts of water. With increasing water scarcity, alternative tillage methods to reduce water use are needed. Dry tillage prior to flooding can reduce water requirements substantially by filling cracks and disrupting bypass flow pathways. It has become apparent that soils have often been puddled excessively. On clay soils, sufficient reduction in hydraulic conductivities can be achieved with only one pass of the puddling implement, but coarser textured soils may require several passes. Landscapes with very shallow water tables may not need puddling at all, while broad cast planting of pre-germinated seed can save labor without sacrificing yield. In the context of rice and upland crop rotations, minimizing puddling to reduce soil structural degradation will benefit post-rice crops such as legumes or wheat.

Radrizzani AB, Shelton HM, Dalzell AC, Kirchhof G (2011). Soil organic carbon and total nitrogen under Leucaena leucocephala pastures in QueenslandCrop & Pasture Science, 2011, 62, 337–345.

Soil organic carbon (OC) and total nitrogen (TN) accumulation in the top 0–0.15m of leucaena–grass pastures were compared with native pastures and with continuously cropped land. OC and TN levels were highest under long-term leucaena–grass pasture (P 20 years old had negative GHG balances; lower additional topsoil OC accumulation rates compared with native grass pastures failed to offset animal emissions.

Liu Y, Sabboh H, Kirchhof G, Sopade P (2010). In vitro starch digestion and potassium release in sweet potato from Papua New Guinea. International Journal of Food Science and Technology 2010, 45, 1925–1931.

Twenty samples of sweet potato from Papua New Guinea, made up of cultivars 3-mun, Carot kaukau, Wahgi besta, Nillgai, Baiyer kaukau, and 1-mun from three provinces, three farmers, and three locations, were subjected to an in vitro starch digestion procedure. Digestion of starch was studied by glucometry, while potassium release was monitored using electrochemistry. The potassium content of the nondigested samples ranged from 4 to 17 mg g)1 dry solids, while the starch content was from 47 to 80 g per 100 g dry solids and independent of G · E effects. In vitro starch digestibility (2–75 g digested starch per 100 g dry starch) significantly (P

Bah R.A, Kravchuk O., Kirchhof G. (2009). Fitting Performance of Particle-size Distribution Models on Data Derived by Conventional and Laser Diffraction Techniques. Soil Science Society America Journal. 73, 1101-1107

Mathematical description of most classical particle size distribution (PSD) data is often used for estimating soil hydraulic properties. Fast laser diffraction (LD) techniques now provide more detailed PSDs, but deriving a function to characterize the entire range of sizes is a major challenge. The aim of this study was to compare the fitting performance of seven PSD functions with one to four parameters on sieve-pipette and LD data sets of fine-textured soils. The fits were evaluated by the adjusted R2, MSE, and Akaike’s information criterion. The fractal and exponential functions performed poorly while the performance of the Gompertz model increased with clay content for the LD data sets. The Fredlund function provided very good fits with sieve-pipette PSDs but not the corresponding LD data sets, probably due to underestimation of the clay fraction in the latter. The two-parameter lognormal function showed better overall performance and provided very good fits with both sieve-pipette and LD data sets.

Bah R.A., Karvchuk O, Kirchhof G. (2009). Sensitivity of drainage to rainfall, vegetation and soil characteristics. Computers and Electronics in Agriculture, Volume 68, Issue 1, August 2009, Pages 1-8.

Rainfall, vegetation characteristics and soil hydraulic properties influence deep drainage patterns in agricultural landscapes, but more information is required on the variability of their interactions with site conditions. Therefore, the objective of the study was to investigate the impact of the interactions of soil permeability, vegetation rooting depth and growth duration on drainage in 3 sites in northern New South Wales, Australia. Local sensitivity analysis was used on drainage estimated by two biophysical models—WaterMod 3, with a crop growth module, and HYDRUS-1D without a crop growth module. The effect of saturated hydraulic conductivity (Ks), growth duration (GD), rooting depth (RD), annual rainfall, and their interactions on deep drainage was evaluated at 3 sites. Simulations were conducted using 30 years of randomly selected climate data from 115 years historical data. Rainfall variability was similar in all 3 sites, so annual rainfall was the dominant factor dictating drainage in all 30 rainfall years whereas GD was more important than RD after accounting for rainfall and drainage was least sensitive to Ks. The minor impact of RD was ascribed to the soil water content being at the lower extraction limit of crops due to potential evaporation being greater than rainfall in almost all months of the rainfall-year. The importance of GD varied between rainfall-years and sites, and was generally higher at high annual rainfall. We conclude that the level of precision at which model inputs are defined would vary with annual rainfall level. Therefore, GD could be defined on a rough scale in low rainfall zones, whereas more precise definitions are necessary at high rainfall. This would depend on classification of rainfall zones based on reliable rainfall data.

Junge, Deji, Abaidoo, Chikoye, Stahr, Kirchhof, OVERVIEW ABOUT SOIL CONSERVATION TECHNOLOGIES AND THEIR PERCEPTION BY FARMERS IN NIGERIA, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof, p49-59. (http://www.aciar.gov.au/publication/TR71)

In Nigeria, West Africa, soil degradation has been one of the most critical environmental problems for a long time. Hence, there has been and still is an urgent need to develop effective soil resource management systems that can reverse the trend. Sustaining soil productivity will enhance food security and alleviate poverty. An extensive literature search that started in 2006 has shown that soil conservation has a long tradition, and earlier and present initiatives have resulted in various on-farm and off-farm technologies. As these have rarely been evaluated to establish adoption rates, an assessment study was performed in 2007 to analyse the effectiveness and adoption of past and present soil conservation initiatives. Villages with different types of conservation technologies were visited and farmers in south-west Nigeria were interviewed to obtain information on their experiences. Mulching, cover cropping and contour tillage are likely to be effective on-farm soil conservation measures practised in Nigeria. They are generally adopted by farmers as they are compatible with the existing farming system, and cheap and easy to install and maintain. Education, knowledge on soil conservation, labour availability and membership in organisations have a positive influence on the adoption rate of technologies.

Kirchhof G, (2009) Editor, Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, ACIAR Technical Reports 71, 126p (http://www.aciar.gov.au/publication/TR71)

High population growth is a problem in most developing countries. Projections for many countries are that the increased demand for food will outstrip the capacity of the land to produce that food. In Papua New Guinea (PNG) the population has doubled since 1966 and the current growth rate is around 2.7%. Despite this high growth rate, the area under agricultural production has remained stable, but land use has intensified. Fallow periods have decreased from several decades to less than one decade. This trend towards more continuous cropping systems is linked to high population densities—as the population increases, the demand for food and cash crops increases. Thus, the need to identify promising management practices to expand both food and cash crops, while sustaining soil fertility, is becoming increasingly important for PNG. This problem is not new: nor is it unique to PNG. Theoretical solutions to the problem of increasing crop productivity while sustaining soil productivity exist, but often they are not applicable to the local agroecological and socioeconomic conditions. For example, use of mineral fertiliser could easily offset production constraints due to depletion of nutrients as a result of continuous cropping, but fertiliser is not accessible for most resource-poor farmers in PNG. Therefore, novel integrated soil-, crop-, nutrient- and water-management practices best suited to local conditions should be developed, pilot tested and transferred to the farmers. Prior to engaging in research to improve or overcome soil constraints, it is imperative to understand current land management systems and the socioeconomic drivers behind these systems. Surveys of farmers play an important role in understanding their current practices and identifying the main constraints to increasing crop productivity. Such information is beneficial in the investigation of management practices that optimise the integrated use of all locally available nutrient sources for sustainable crop production, but have minimal adverse effects on the environment. This report summarises the results from a pilot study on soil fertility management funded by the Australian Centre for International Agricultural Research (ACIAR), and reviews sweetpotato-based cropping systems in the highlands of PNG. It also describes the lessons learnt from survey methodologies used to assess the socioeconomic and biophysical constraints to sweetpotato production in this area. Case studies from similar surveys done in Nigeria and northern New South Wales, Australia, are included as examples.

Kirchhof, Daniells, CHANGING TILLAGE MANAGEMENT PRACTICES AND THEIR IMPACT ON SOIL STRUCTURE PROPERTIES IN NORTH WESTERN NEW SOUTH WALES, AUSTRALIA, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof p60-69. (http://www.aciar.gov.au/publication/TR71)

A study was conducted in 1998 in north-western New South Wales to assess how changes in tillage practices and farmers’ perceptions of ‘good’ or bad’ paddocks relate to soil structural properties. Forty landholders were visited and interviewed to obtain background information on their current and past management practices, crops and cropping systems used, and what they expect in the future. The majority of the soils were Vertosols (78%), with some Kandosols and a few Chromosols. Conventional tillage was practised on 63% of the fields surveyed. Conservation tillage (minimum or zero-tillage) was only practised on swelling clay soils. On these soils 26% of the fields had been converted from conventional to conservation tillage during the past 3 years, while on 14% of the fields conservation tillage had been practised since they were brought into crop production (3–10 years previously). Saturated hydraulic conductivities on the farmed black Vertosols with a history of conventional tillage were lower than those of the virgin sites, but increased after conversion from conventional to conservation tillage. Fields that were brought into cropping during the last 10 years using conservation tillage only had higher saturated conductivities than the virgin sites. There was little effect of cropping history on saturated hydraulic conductivity on the grey Vertosols. Soil organic carbon on the control sites was always greater than on the corresponding cultivated sites, regardless of whether conventional or conservation tillage was practised. Tillage history did not affect any of the measured soil chemical properties. Platyness of soil structure was a clear indicator for wheel-induced compaction. Platy structure was not shown on any of the swelling clay soils at the never-cultivated sites, and tended to be more frequent on the ‘poor’ sites. This was most pronounced for the grey Vertosols, where 80% of the ‘poor’ and 50% of the ‘good’ sites were platy, and on the black Vertosols, with 42% and 31% respectively. The overall close agreement between platyness and the farmers’ perceptions of ‘good’ and ‘poor’ sites indicated that platyness has an impact on soil productivity and that soil compaction continues to be a limiting factor for crop production. We also concluded that black Vertosols respond better to conservation tillage than grey Vertosols, possibly due to their greater resilience and better ability to self-ameliorate. The absence of conservation tillage adoption on non-swelling clay soils in this region (at the time of the study) may reflect the length of time required before conservation tillage improves soil structure and, ultimately, yield.

Kirchhof, Odunze, Salako, SOIL MANAGEMENT PRACTISES IN THE NORTHERN GUINEA SAVANNA OF NIGERIA, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G. Kirchhof, p43-48. (http://www.aciar.gov.au/publication/TR71)

A survey of soil management practices was conducted in the northern Guinea savanna of Nigeria. Fifteen villages were randomly selected from a geographical grid covering an area of 100 × 200 km located in the benchmark area of the Ecoregional Program for the Humid and Sub-humid Tropics of Sub-Saharan Africa. In each village the chief and several farmers were interviewed to assess their soil management methods and attitude towards the need to conserve soil. A total of 181 farmers were interviewed in late 1996. The most common crop rotation systems were food legumes with non-legume crops (40%), followed by monocropping (28%). Fifty-three per cent of the farmers who included food legumes in their rotations did so for soil fertility considerations, while 49% of the farmers who practised monocropping did so to maximise their output. These practices indicate that farmers were well aware of the importance of legumes for maintaining soil fertility. Only 2% of the farmers practised mulching with crop residue. The most common use of crop residue was for fodder, the remainder largely being used as building material or else burnt. As a consequence, soil surfaces were generally bare at the onset of the rainy season and hence prone to soil erosion. Ridging was the most important land preparation technique (88%), with farmers perceiving benefit in terms of improved crop emergence (56%) and water conservation (11%). Other benefits included weed control. Ridging was generally practised along contours, with most farmers citing soil conservation benefits, e.g. water conservation, and erosion control as the reasons for using contour ridging. Those farmers who purposely ridged up and down the slope did so for drainage purposes. All farmers used the same method to build ridges—the ridge from the previous year was cut in the middle and the two halves of neighbouring ridges were combined to form a new ridge in the furrow from the previous year. According to the farmers, this method controlled weeds and improved emergence. None of the farmers practised rebuilding old ridges, similar to permanent ridges. Such a practice might be acceptable to farmers in that it may be less labour intensive to rebuild partially collapsed ridges compared to reridging completely. Soil physical benefits from semi-permanent ridging would include increased soil structural stability, reduced soil compaction and increased root proliferation into the subsoil. Negative side effects might include reduced crop emergence and increased weed infestation. The most commonly used tools for soil preparation were hand hoes (80%), followed by draft animals (16%) and tractors (3%).

Kirchhof, Taraken, Ramakrishna, Ratsch, Igua, BIOPHYISCAL CONSTRAINTS OF SWEET POTATO BASED CROPPING SYSTEMS IN THE PNG HIGHLANDS, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof p95-109. (http://www.aciar.gov.au/publication/TR71)

Population growth in the Paua New Guinea highlands is among the highest in developing countries. While the 2000 census reported a rate of 3%, more realistic estimates may be closer to 2%. Even if exact rates are unknown, the trend of expanding population will continue and could result in a doubling of the population to around 4 million in just over 3.5 decades. This will place unprecedented pressure on the land resource. However, it is still unclear if the resource-base ‘soil’ is indeed being depleted at a greater rate than it can be restored, given the potentially high productivity of the soils in the region. We surveyed farmers and assessed their gardens to evaluate if soil fertility and associated production of the most important staple food, sweetpotato, is indeed declining as a consequence of increasing land pressure, shortening fallow periods and a number of other factors, including pests and diseases. This survey included 95 farmers in four highlands provinces with an average of three districts in each province. Farmers’ perceptions on soil fertility decline and management options were obtained. They were then asked to show us one garden that had recently been brought back into production after fallow, the ‘new’ fertile garden, and another garden that was about to go into fallow, the ‘old’ run-down garden. Plant and soil samples were collected from these two gardens to quantify changes as a result of cropping over time.

Kirchhof, Taraken, Ratsch, Kapal, Igua, SURVEY METHODOLOGY TO ASSESS SOCIO-ECONOMIC AND BIOPHYSICAL CONSTRAINTS – LESSONS LEARNT IN THE PNG HIGHLANDS, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof p70-78. (http://www.aciar.gov.au/publication/TR71)

Among developing countries, Papua New Guinea (PNG) has one of the highest population growth rates. As land under cultivation has been stable for decades, the increasing demand for food is placing unprecedented pressure on the land resource under agriculture. An exploratory farmer survey in the highlands of PNG was conducted to assess farming practices in relation to soil productivity decline over time as population increases. The survey comprised farmer interviews as well as the collection of a biophysical dataset, including soil and plant analyses, to underpin farmer perceptions of a potential problem regarding soil fertility. Unlike most farmer surveys, this survey combines socioeconomic data with biophysical measurements. This type of exploratory survey was considered to be necessary to delineate the need for further research intervention. The baseline dataset is also useful to measure post-project impact and adoption, which is often inferred from auxiliary data if baseline data are missing. A main deficiency of the exploratory survey was bias in sample location caused by village access problems and safety concerns. The willingness of farmers, male or female, to participate in the interviews, and sample collection for the biophysical assessment of their gardens, were not problems.

Kravchuk , Wilson, Kirchhof, Statistical methods for a soil fertility management survey analysis in Papua New Guinea, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof p79-87. (http://www.aciar.gov.au/publication/TR71)

This paper is a short communication about methods used in the analysis of biophysical data from the scoping stage of a soil fertility management survey in Papua New Guinea conducted in September–October 2005 (Australian Centre for International Agricultural Research project SMCN/2005/043). The goal of this communication is to describe and promote the good practice of statistics in application to biophysical surveys. A step-by-step analysis is presented of the difference in sweetpotato yield between newly established gardens and gardens that have been cultivated for a long period. We comment on the strengths and limitations of statistical techniques used in the analysis, and also relate the techniques to the corresponding software procedures (R15, Minitab Inc., Chicago). Although we refer to various general methods, the analysis presented is specific to one particular survey. This paper may be useful for agricultural researchers as a case study of the data analysis of field surveys in research or extension projects.

Liu Y, Sabboh H, Kirchhof G, Sopade PA. (2009). Digestibility of starch and potassium in sweetpotato from Papua New Guinea. Proceedings, 15th Triennial Symposium of the International Society for Tropical Root Crops, 2-6 November 2009, International Potato Centre, Lima, Peru.

Potassium is a major mineral in sweetpotato, and like most root crops, sweetpotato has high starch content. There are many cultivars of sweetpotato with genotype and environmental differences, which influence digestibility and bioavailability. Starch and mineral digestibility in food materials are currently topical because of associated nutritional implications. Time-course in-vitro starch and potassium digestibility of 20 samples of sweetpotato from Papua New Guinea were studied using glucometry and electrochemistry/spectroscopy respectively. The samples were made up of six cultivars (3-mun, Carot kaukau, Wahgi besta, Nillgai, Baiyer kaukau, and 1-mun) planted in three provinces by three farmers in three different locations. The potassium content of the non-digested samples ranged from 4 – 17 mg/g dry solids, while the starch content was from 47 – 80 g per 100g dry solids and essentially independent of cultivars, farmers and locations. In-vitro starch digestibility (2 – 75 g digested starch per 100g dry starch) significantly (p

Ramakrishna, A., Bailey, J.S. & Kirchhof, G. (2009). A preliminary diagnosis and recommendation integrated system (DRIS) model for diagnosing the nutrient status of sweet potato (Ipomoea batatas). Plant and Soil. 316, 107-116.

Critical leaf nutrient concentrations have often been used to diagnose the nutritional causes of crop underperformance. Unfortunately, these diagnostic criteria are not available for mature, tuber-bearing sweet potato plants (the word ‘tuber’ being used to describe a swollen root rather than a swollen stem). The Diagnosis and Recommendation Integrated System (DRIS), however, provides a reliable means of linking leaf nutrient concentrations to the yield of sweet potato tubers, and may be developed for this crop using existing data from regional crop surveys. In the present study, tuber yield and leaf nutrient concentration data from a survey of sweet potato gardens conducted in the Papua New Guinea (PNG) highlands in 2005 were used to establish DRIS N, P, K, and S norms and statistical parameters for sweet potato. Although the database was relatively small, the norms derived for nutrient ratios of key biological significance, i.e. N/S and K/N, were within the expected narrow ranges for higher plants, giving credibility to both the database and the DRIS model. Data from future surveys and field trials may subsequently be used to enlarge the database allowing the refinement of model parameters and hopefully an expansion of diagnostic scope to include other macro and micro-nutrients. As it stands, though, this preliminary DRIS model for sweet potato is possibly the best diagnostic tool currently available for evaluating the N, P, K and S statuses of sweet potato crops in the pacific region.

Wegener, Kirchhof, Wilson, SOCIO-ECONOMIC ANALYSIS OF VILLAGE GARDEN MANAGEMENT IN THE PNG HIGHLANDS, IN: Soil fertility in sweet potato-based cropping systems in the highlands of Papua New Guinea, 2009, ACIAR Technical Reports 71, Editor G.Kirchhof p88-94. (http://www.aciar.gov.au/publication/TR71)

A survey of approximately 100 village gardeners in the Papua New Guinea (PNG) highlands was conducted in 2005 as a preliminary step in setting up an Australian Centre for International Agricultural Research project to improve the nutrition of sweetpotato in the highlands. Sweetpotato is the main staple crop in the PNG highlands, which had a population of around 2 million (or 40% of the country’s population) at the 2000 census, with around 2–3% annual growth. Despite these high growth rates, the area under agricultural production has remained fairly static, resulting in increasing pressure on land resources. Farmers are concerned about yield decline, as sweetpotato yields from fallowed land, or land recently brought back into production as part of the recycling of gardens that occurs in the highlands, tend to be much higher (2–8 t/ha tubers) than yields from old gardens. Despite high apparent nutrient stocks and favourable carbon:nitrogen ratios in the soil, most sweetpotato tissue samples have shown low nutrient levels, in particular of nitrogen, phosphorus, potassium and boron. The survey was conducted to assemble background information on farm locations, farm practices, crop yields, and soil and plant analysis. The conceptual framework proposed to guide the analysis was that background factors (such as location, garden type, land availability, age and sex of farmer, number of children in household and sources of other income) affect management practices. These management practices (soil preparation, planting system, fertility management including fallowing, use of animals such as goats and pigs in the farming system, and crop rotations) influence outcomes such as plant and soil analyses; sweetpotato yields; plant symptoms; tuber characteristics such as weight, size, colour and cracking; presence of nematodes; and ability to grow other crops. A preliminary analysis of the survey data has been conducted and results are reported in this paper.

Bailey, J.S., Ramakrishna A. & Kirchhof, G. (2008). Relationships between important soil variables in moderately acidic (pH = 5.5) soils in the highlands of Papua New Guinea and management implications for subsistence farmers. Soil Use and Management. 24, 281-291.

The fertility of farmed soils in parts of the Papua New Guinea (PNG) highlands reputedly has been declining for some time owing to population pressure. To assess the extent of the problem, a survey of sweet potato gardens was conducted across four of the highlands provinces and information on soil variables was obtained for gardens on soils of volcanic and non-volcanic origins. In the absence of fertilizer application, soil fertility in the humid tropics is largely a function of soil cation exchange capacity (CEC), and soils of low CEC had previously been reported in this region. In the present study, relationships between effective CEC (ECEC) and other soil properties in moderately acidic soils (pH 5.5–6.3) were investigated to see if there was scope for improving soil cation retention characteristics through management of key soil variables. For volcanic soils of varying allophane content, ECEC was, unexpectedly, negatively correlated with soil C and soil C/ N, most probably because of the formation of humus–allophane complexes which had facilitated organic matter accumulation whilst dramatically reducing the free negative charges on the material. Given the latter outcome, the indigenous practice of heaping compost in the centre of soil mounds appeared to be one of the best strategies for circumventing the problem of low CEC, as nutrients in the compost are held in an environment virtually independent of the surrounding soil mineralogy. Although the positive correlation between soil pH and soil ECEC was weak for volcanic soils, it was concluded that liming might nevertheless be an effective means of enhancing the nutrient retention characteristics of these soils provided the practicalities and costs were not prohibitive.

Bailey, J.S., Ramakrishna, A. & Kirchhof, G. (2008). An evaluation of nutritional constraints on sweet potato (Ipomoea batatas) production in the central highlands of Papua New Guinea. Plant and Soil. 316, 97-105.

Sweet potato (Ipomoea batatas) is the staple food crop in the highlands of Papua New Guinea (PNG). Declining crop productivity, however, appears to be threatening the sustainability of sweet potato-based farming systems within the region, a probable cause being the exhaustion of soil nutrient reserves in continuously cultivated sweet potato gardens. To assess the extent of the problem, a survey of sweet potato gardens was conducted across four of the highlands provinces and information on soil and crop variables was obtained for old gardens (cultivated over many seasons) and new gardens (newly brought into cultivation) on soils of volcanic and non-volcanic origin. Crop leaf nutrient data collected in the survey were interpreted using the Diagnosis and Recommendation Integrated System (DRIS), to try to identify the main nutritional constraints on tuber production in different garden types on soils of volcanic or non-nonvolcanic origin. The results suggested that K deficiency was the primary cause of poor crop production in almost a third of sweet potato gardens, but was more of a problem in old gardens than in new. Phosphorus deficiency was also a problem on volcanic soils, and S deficiency on non-volcanic soils. These latter deficiencies, however, were at least as prevalent in new gardens as in old. Important factors contributing to K and S depletion from garden systems were the removal of K and S-rich vines from cultivation areas, the shortening of fallow periods and the burning of weed and crop residues, the latter releasing S (SO2) to the atmosphere. Correction of K and S deficiencies may require the recycling of old vines back to sweet potato cultivation areas and the adoption of a zero-burn policy for fallow management. Correction of P deficiency may necessitate the use of P-accumulating fallow species, e.g. wild Mexican sunflower (Tithonia diversifolia), to extract the P fixed by sesquioxide and allophanic minerals.

Beal CD, Rassam DW, Gardner EA, Kirchhof G, Menzies NW. (2008). Influence of Hydraulic Loading and Effluent Flux on Surface Surcharging in Soil Absorption Systems. Journal of Hydrologic Engineering. 13:8, 681-692.

The goal of this study was to investigate how extreme hydraulic loading influences hydraulic pathways, and thus failure potential, of two soil absorption systems. A grid of tensiometers and piezometers were installed beneath and adjacent to the absorption trenches, and water height was manipulated to simulate different hydraulic loadings. At both sites, measured soil matric potentials along the trench sidewalls increased toward zero as water height increased over time, indicating that water was preferentially flowing laterally above the biomat zones. Saturated hydraulic conductivity Ks of the soil and biomat, and other hydraulic parameters were calibrated using inverse modeling procedures in HYDRUS-2D. We found generally good agreement between measured and predicted matric potentials. The calibrated model was then used to predict fluxes through different infiltrative zones under typical and extreme hydraulic loads. Modeling indicated that the overall infiltration rates through the biomat and subbiomat zones fell within a relatively narrow range of 0.025–0.046 m/day at the two sites. Under extreme hydraulic loading to trenches, fluxes through the upper trench sidewalls i.e., the exfiltration zone were predicted to be substantially greater i.e., 80% of total flux than through the biomat zone. This confirms the conclusions made from field results, that a permeable exfiltration zone provides a critical buffer to surface surcharging during extreme trench loading. Conversely, the presence of a high sidewall biomat can reduce sidewall exfiltration of effluent, and therefore increase the likelihood of surface surcharging.

Kirchhof G, Ramakrishna A (2008). Analysis of biophysical and socio-economic constraints to soil fertility management in the PNG Highlands. Final report – ACIAR project SMCN 2005/043. 37p. http://www.aciar.gov.au/project/SMCN/2005/043

Project Background and Objectives In Papua New Guinea's highlands, soils are rich and productive. Both crop production and agroforestry are widely practiced. The most extensively grown crop is sweet potato, the main food staple, cultivated on between 50 and 90 per cent of arable land. Recent declines in sweet potato yield suggest soil fertility is also declining. Pests and diseases may play a role, as may the shortening of fallow periods to cater for increased cropping to feed a growing population. Understanding the factors contributing to soil fertility and sweet potato yield decline is needed to guide future R&D activities. Information to build this understanding was collected to determine these factors, including the socio-economics of farmer decision-making. Project Outcomes The project team surveyed farmers and assessed their gardens to evaluate if soil fertility and associated production of the most important staple, sweet potato, was indeed declining as a consequence of increasing land pressure, shortening fallow periods and a number of other factors including pests and diseases. This survey included 95 farmers in four Highland provinces with an average of three villages in each province. Farmer's perceptions on soil fertility decline and management options were obtained. They were then asked to show the team one garden which had recently been brought back into production after fallow, the 'new' fertile garden, and another garden which was about to go into fallow, the 'old' run-down garden. Plant and soil samples were collected from these two gardens to quantify changes as a result of cropping over time. Sweet potato yields Sweet potatoes are harvested sequentially, making it notoriously difficult to obtain reliable yield data. The team used single harvest yields to assess relative production from this 'one-off' farmer survey. In both gardens, old and new, single harvest yields of up to 30 t/ha were observed with a median yield of 6 t/ha. Due to the sequential harvesting these yields were considerably lower than the average total yields of 13-15t/ha for lowland and highland systems reported by Bourke and Vlassak (2004). The large variation in the measured yields and cultivars prevented the use of covariates such as number of previous harvests and age of sweet potato plant to estimate total yields. However the team's observations were similar to others (2006) from an EU funded project on early maturing sweet potato varieties in the lowlands executed by NARI. Likely causes for the low yields were nutrient deficiencies, pests and diseases and presence of viruses in the sweet potato planting material (traditional and improved). Nutrient deficiencies were evident even though the predominantly volcanic ash soils in the Highlands are regarded as very fertile soils. In a 1997 study more than 50% of sweet potato tissue samples collected were deficient in N, P, K, S and B. Unclean planting material is also a major contributing factor to low yield, but it is unclear if pathogen-tested varieties would suffer nutrient deficiencies comparable to traditional varieties. Yield trends in old and new gardens Pests and diseases: The cause for low yields in old gardens? There was no difference in the degree of insect infestation of tubers between the old and new gardens (p=13%). There was also no significant difference in the expected percentage of cracked tubers between the old and new gardens (p-value > 7%). But the average yield of vines with cracked tubers was higher in the new gardens, indicating that new gardens produce higher yields even though tubers may have cracks. Despite higher yields, the new gardens tended to have larger counts of nematodes (p=5%), suggesting that the nematodes could be either non-parasitic or infestation is not a critical factor driving yield. The distribution of weevils was significantly different between the old and new gardens. The chances of the presence of weevils or larvae are significantly higher in the old garden (p-value 2200m) showed that high altitudes have considerably higher total N and soil organic carbon (SOC) than the lower. Despite these subtle differences in apparent soil fertility they had no impact on sweet potato yield. This is of particular interest because SOC is often regarded as an important indicator for soil health and fertility. Farmers perception The farmer's response to the survey was a strong willingness to cooperate. Farmers related yield reduction to soil fertility decline and were eager to collaborate as partners and requested feedback from our work. Their observation was that yields in older gardens are lower than in newer gardens and they blamed poor soil conditions for this decline. We asked farmers whether they could grow corn or common bean as a control question to assess their ability to judge soil fertility. The responses to both questions were closely related and farmers thought that the new gardens were more suitable for growing corn or common bean than the old gardens (corn p=4%, bean p=8%). However, the farmer's soil fertility assessment was not related to the sweet potato yields we observed, but it supported the argument that soil fertility differences exist between old and new garden. Soil fertility management and planting systems Yields in the new gardens were not affected by planting systems, but yields in the old gardens were highest if farmers used large mounds. In both, old and new gardens, mounds more than 70 cm high were associated with fertility management such as composting and short fallow (in old gardens). The high mounds system was mostly associated with high altitude. However, the difference in planting systems does not explain all the effect of altitude (p

Kirchhof G, Ramakrishna A (2008). Soil fertility assessment of soils in the highlands of Papua New Guinea. Paper. Soils2008 Conference – Soil, the living skin of planet Earth. Palmerston North, New Zealand, 1 – 5 Dec 2008. http://www.soilsconference.co.nz/page.php?17

The population in PNG highlands has increased on an average at 2.8% during 1980-2000 (National Statistical Office, 2002) and is amongst the highest in developing countries. The trend is likely to continue in the near future and could reach 4 million by 2020. Despite high population growth, the arable land for agricultural production has remained relatively stagnant (Bourke 1997, 2001) with concomitant intensification of land use and reduced fallow periods. Most agriculture systems in Papua New Guinea are variations of shifting cultivation systems, usually between 15 and 25 years long, compared to one to two years of cultivation. However, population pressure has resulted in reduction in fallow periods from several decades to less than one decade (Sam, 1996). In the long term, one can anticipate further shortening of fallow periods and lengthening of cropping cycles. There are already indications that soil fertility run-down is impacting on the productivity of the main staple in the area, sweet potatoes, which accounts for 55 to 90% of land under arable agriculture. However, at this stage it is still unclear wether the resource base ‘soil’ is indeed being depleted at a greater rate than it can be restored given the potentially high productivity of the soils in the region.

Kirchhof, G, Ramakrishna, A, & Bailey J.S. (2008). An evaluation of Colwell-P as a measure of plant available phosphorus in soils of volcanic and non-volcanic origin in the highlands of Papua New Guinea. Soil Use and Management. 24, 331-336.

Various soil test methods including Olsen, Colwell, Bray and Truog have been used to assess the levels of plant-available P (PAP) in soils situated in the highlands of Papua New Guinea (PNG). Up until now, though, there has been no guarantee that these tests provide valid assessments of PAP in these somewhat atypical organic matter-rich tropical soils. Furthermore, the critical soil-P concentrations associated with the tests have been based on studies conducted elsewhere in sub-tropical and temperate latitudes and as such may or may not be valid for soils or cropping situations in PNG. Soil (Colwell)- P and leaf-P data collected during a recent survey of sweet potato gardens in the highlands of PNG were therefore used to determine if useful relationships existed between these variables for different groups of soils, and if they do, to use these relationships to evaluate critical soil Colwell-P concentrations corresponding to a known critical concentration of P in sweet potato index leaf tissue. Separate, highly significant linear relationships were obtained between leaf-P and Colwell-P for soils of volcanic and non-volcanic origins. Based on these relationships, the critical Colwell-P concentration for volcanic soils was found to be four times greater than that for non-volcanic soils, presumably because much of the P extracted from the former soils with alkaline sodium bicarbonate had been chemically ‘fixed’ via sorption and precipitation reactions with sesquioxides and rendered unavailable to plants at ambient soil pH. These critical Colwell-P concentrations if adopted as benchmark values for the soil groups in question should ensure that the results of future soil fertility surveys involving Colwell-P assessments are correctly interpreted.

Ramakrishna, A. & Kirchhof, G. (2008). An evaluation of nutritional constraints on sweet potato (Ipomoea batatas) production in the central highlands of Papua New Guinea. Plant and Soil. 316, 97-105.

Sweet potato (Ipomoea batatas) is the staple food crop in the highlands of Papua New Guinea (PNG). Declining crop productivity, however, appears to be threatening the sustainability of sweet potato-based farming systems within the region, a probable cause being the exhaustion of soil nutrient reserves in continuously cultivated sweet potato gardens. To assess the extent of the problem, a survey of sweet potato gardens was conducted across four of the highlands provinces and information on soil and crop variables was obtained for old gardens (cultivated over many seasons) and new gardens (newly brought into cultivation) on soils of volcanic and non-volcanic origin. Crop leaf nutrient data collected in the survey were interpreted using the Diagnosis and Recommendation Integrated System (DRIS), to try to identify the main nutritional constraints on tuber production in different garden types on soils of volcanic or non-nonvolcanic origin. The results suggested that K deficiency was the primary cause of poor crop production in almost a third of sweet potato gardens, but was more of a problem in old gardens than in new. Phosphorus deficiency was also a problem on volcanic soils, and S deficiency on non-volcanic soils. These latter deficiencies, however, were at least as prevalent in new gardens as in old. Important factors contributing to K and S depletion from garden systems were the removal of K and S-rich vines from cultivation areas, the shortening of fallow periods and the burning of weed and crop residues, the latter releasing S (SO2) to the atmosphere. Correction of K and S deficiencies may require the recycling of old vines back to sweet potato cultivation areas and the adoption of a zero-burn policy for fallow management. Correction of P deficiency may necessitate the use of P-accumulating fallow species, e.g. wild Mexican sunflower (Tithonia diversifolia), to extract the P fixed by sesquioxide and allophanic minerals.

Salako, F. K., Tian, G., Kirchhof G. 2008. Soil chemical properties and crop yields on an eroded Alfisol managed with herbaceous legumes under yam-maize rotation. Nigerian Journal of Soil Science 18:1-9

This study was carried out in Ibadan, southwestern Nigeria between 1997 and 1999 to determine changes in soil chemical properties and yields on a previously eroded Alfisol. A factorial experiment in which legumes (Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides) and residue management (burned and mulched residues) were factors was set up in two replicates of runoff plots. Yam was planted in 1997 and 1999 whereas maize + legume intercrops were planted in 1997. Soil properties measured were particle size distribution, pH, organic C, total N, Ca, Mg, Mn, exchangeable acidity and effective cation exchange capacity. There was increased acidity at the site. Soil chemical properties were significantly improved by burning of cowpea and Pueraria residues and mulching with Mucuna. Yam tuber yields of 14-18 t ha-1 in 1997 was

Salako EK, Olowokere EA, Tian, G Kirchhof, Osiname O. (2007). Ground cover by three crops cultivated on marginal lands in southwestern Nigeria and implications for soil erosion. Spanish Journal of Agricultural Research. 5, 497-505.

Resource-poor farmers in developing nations cultivate marginal lands, thereby exacerbating the problem of soil degradation through poor plant growth and ground coverage. An assessment of ground cover under such a practice will provide a guideline for soil conservation. Ground cover by leguminous cover crops (e.g., Mucuna pruriens, Pueraria phaseoloides and Vigna unguiculata), associated with yam, maize and rice was measured in three different experiments in southwestern Nigeria using beaded-string method while leaf area was measured using a flat-bed scanner. The leaf area was used in obtaining equivalent of ground cover fraction from the leaf area index. Ground cover by yam was

Salako, E. K., E. A. Olowokere, Tian, G., Kirchhof, G. Osiname, O. (2007). Ground cover by three crops cultivated on marginal lands in southwestern Nigeria and implications for soil erosion. Spanish Journal of Agricultural Research 5(4): 497-505.

Resource-poor farmers in developing nations cultivate marginal lands, thereby exacerbating the problem of soil degradation through poor plant growth and ground coverage. An assessment of ground cover under such a practice will provide a guideline for soil conservation. Ground cover by leguminous cover crops (e.g., Mucuna pruriens, Pueraria phaseoloides and Vigna unguiculata), associated with yam, maize and rice was measured in three different experiments in southwestern Nigeria using beaded-string method while leaf area was measured using a flat-bed scanner. The leaf area was used in obtaining equivalent of ground cover fraction from the leaf area index. Ground cover by yam was

Bah A.R, Kravchuk O., Kirchhof G (2006). Impact of saturated hydraulic conductivity and rainfall on variability of predicted drainage. ASSSI - ASPAC - ACMS National Soils Conference - Soil Science Solving Problems. The University of Adelaide, North Terrace, 3-7 December 2006. Poster paper

Accurate targeting of measures to control deep drainage requires information on its spatial and temporal variability across landscapes. This is partly related to the variability of soil hydraulic characteristics and rainfall conditions. The aim of the study was to evaluate the effect of the variability of saturated hydraulic conductivity ( ) on the accuracy of drainage predicted under different rainfall conditions. Numerical studies, wherein variability within soil layers and rainfall was controlled, were conducted using a semi-mechanistic, one-dimensional water balance model (WaterMod 3). Our results suggest that the variability in significantly contribute to the variability in drainage in clay soils (>30% clay) but has little influence on that for sandy soils. It was also deduced that the soil structure should be taken into account when predicting the variation in drainage.

Beal CD, Gardner T, Kirchhof G, Menzies NW (2006) Long term flow rates and biomat zone hydrology in soil columns receiving septic tank effluent. Water Research 40, 2327-2338

Soil absorption systems (SAS) are used commonly to treat and disperse septic tank effluent (STE). SAS can hydraulically fail as a result of the low permeable biomat zone that develops on the infiltrative surface. The objectives of this experiment were to compare the hydraulic properties of biomats grown in soils of different textures, to investigate the long-term acceptance rates (LTAR) from prolonged application of STE, and to assess if soils were of major importance in determining LTAR. The STE was applied to repacked sand, Oxisol and Vertisol soil columns over a period of 16 months, at equivalent hydraulic loading rates of 50, 35 and 8 L/m2/d, respectively. Infiltration rates, soil matric potentials, and biomat hydraulic properties were measured either directly from the soil columns or calculated using established soil physics theory. Biomats 1 to 2 cm thick developed in all soils columns with hydraulic resistances of 27 to 39 d. These biomats reduced a 4 order of magnitude variation in saturated hydraulic conductivity (Ks) between the soils to a one order of magnitude variation in LTAR. A relationship between biomat resistance and organic loading rate was observed in all soils. Saturated hydraulic conductivity influenced the rate and extent of biomat development. However, once the biomat was established, the LTAR was governed by the resistance of the biomat and the sub-biomat soil unsaturated flow regime induced by the biomat. Results show that whilst initial soil Ks is likely to be important in the establishment of the biomat zone in a trench, LTAR is determined by the biomat resistance and the unsaturated soil hydraulic conductivity, not the Ks of a soil. The results call into question the commonly used approach of basing the LTAR, and ultimately trench length in SAS, on the initial Ks of soils.

Kirchhof G. (2006). Plastic Properties. In: Encyclopaedia of Soil Science 2nd revised Edition. Editor: Rattan Lal.

Application of a force to soil can result in an elastic, non-permanent, deformation that only lasts while the force is applied or a plastic, permanent deformation that persists after the load is removed. The latter may, or may not result in a decrease in the soil volume. How easily and how much the volume changes is determined by the soil's plasticity. It is an important factor influencing ease and outcome of soil tillage operations. Soil plasticity is caused by the lubricating film of water surrounding soil particles that allow the soil to change shape without rupturing upon application of forces. As an inherent soil property it is governed primarily by the surface area of the soil particles. Plasticity increases with increasing clay content, activity of clay minerals, position of the adsorbed cations in the lyotropic series and organic matter content.

Salako F.K, Tian G., Kirchhof G., Akinbola G.E. (2006). Soil particles in agricultural landscapes of a derived savanna in southwestern Nigeria and implications for selected soil properties. Geoderma, 137, 90-99.

The vast area of savanna ecology in Africa plays a significant role in food production, making a study of soils in this zone very important. Therefore, soil physical and chemical properties of 14 soil profiles were studied in a derived savanna zone of southwestern Nigeria on 2 toposequences at 2 locations (Ibadan and Alabata), which were 20 km apart. Six soil profiles were studied at Ibadan while 8 were studied at Alabata. Morphological descriptions of profiles were carried out. Data collected included particle size distribution, bulk density, clay dispersion, water retention characteristics, pH, organic carbon, exchangeable K, Ca, Mg and available P. Soil profiles along the toposequences were well developed with depths exceeding 180 cm, except for one profile at the lower slope position where an indurated plinthic layer was found at 68 cm depth. The horizons were easily distinguished with color, texture and consistency. Total sand, with the main component being coarse sand, decreased with depth from 813 to 502 g kg-1 at Ibadan and from 824 to 635 g kg-1 at Alabata. The clay content increased with depth from 54 to 356 g kg-1 at Ibadan and from 63 to 279 g kg-1 at Alabata. Gravel concentration was highest for soil horizons found between 20 and 102 cm depth. Also, bulk density increased with soil depth from 1.35 to 1.51 g cm-3 at Ibadan and from 1.38 to 1.64 g cm-3 at Alabata, indicating that subsoil horizons were more compact due to higher clay and gravel contents, and sticky consistency. The A horizon had a significantly higher water content at water potentials N2 kPa while the subsoils had higher water content at b2 kPa. Soil organic C and total N decreased with soil depth at both locations with the A horizon having significantly higher organic C (7.10–12.69 g kg-1) and total N (0.84–1.2 g kg-1) than deeper horizons (1.9–4.47 g kg-1 for organic C and 0.12–0.58 g kg-1 for N). Particle size distribution was significantly different among the slope positions at both locations. Also, soil water retention, soil pH, total N and exchangeable K were distinguishing parameters among slope positions. The interaction of soil depth and slope position was, however, not significant suggesting that processes influencing soil horizon development acted independently in the vertical and lateral directions. Soil pH was the only attribute that distinguished the toposequences between the two locations.

Salako F.K., Kirchhof G., Tian G. (2006). Management of a previously eroded tropical Alfisol with herbaceous legumes: Soil loss and physical properties under mound tillage. 89, 185-195.

A study was carried out on a previously eroded Oxic Paleustalf in Ibadan, southwestern Nigeria to determine the extent of soil degradation under mound tillage with some herbaceous legumes and residue management methods. A series of factorial experiments was carried out on 12 existing runoff plots. The study commenced in 1996 after a 5-year natural fallow. Mound tillage was introduced in 1997 till 1999. The legumes – Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides – were intercropped with maize in 1996 and 1998 while yam was planted alone in 1997 and 1999. This paper covers 1997–1999. At the end of each year, residues were either burned or mulched on respective plots. Soil loss, runoff, variations in mound height, bulk density, soil water retention and sorptivity were measured. Cumulative runoff was similar among interactions of legume and residue management in 1997 (57–151 mm) and 1999 (206–397 mm). However, in 1998, cumulative runoff of 95 mm observed for Mucuna-burned residue was significantly greater than the 46 mm observed for cowpea-burned residue and the 39–51 mm observed for mulched residues of cowpea, Mucuna and Pueraria. Cumulative soil loss of 7.6 Mg ha 1 observed for Mucuna-burned residue in 1997 was significantly greater than those for Pueraria-mulched (0.9 Mg ha-1) and Mucuna-mulched (1.4 Mg ha-1) residues whereas in 1999 it was similar to soil loss from cowpea treatments and Pueraria-burned residue (2.3–5.3 Mg ha 1). There were no significant differences in soil loss in 1998 (1–3.2 Mg ha 1) whereas Mucuna-burned residue had a greater soil loss (28.6 Mg ha 1) than mulched cowpea (6.9 Mg ha 1) and Pueraria (5.4 Mg ha 1). Mound heights (23 cm average) decreased non-linearly with cumulative rainfall. A cumulative rainfall of 500 mm removed 0.3–2.3 cm of soil from mounds in 1997, 3.5–6.9 cm in 1998 and 2.3–4.6 cm in 1999, indicating that (detached but less transported) soil from mounds was far higher than observed soil loss in each year. Soil water retention was improved at potentials ranging from 1 to 1500 kPa by Mucuna-mulched residue compared to the various burned-residue treatments. Also, mound sorptivity at 1 cm water head (14.3 cm h 1/2) was higher than furrow sorptivity (8.5 cm h 1/2), indicating differences in hydraulic characteristics between mound and furrow. Pueraria-mulched residues for mounds had the highest sorptivity of 17.24 cm h 1/2, whereas the least value of 6.96 cm h 1/2 was observed in furrow of Mucuna-burned residue. Pueraria phaseoloides was considered the best option for soil conservation on the previously eroded soil, cultivated with mound tillage.

Salako, F. K., G. Kirchhof and G. Tian (2006). Management of a previously eroded tropical Alfisol with herbaceous legumes: Soil loss and physical properties under mound tillage. Soil & Tillage Research 89(2): 185-195.

A study was carried out on a previously eroded Oxic Paleustalf in Ibadan, southwestern Nigeria to determine the extent of soil degradation under mound tillage with some herbaceous legumes and residue management methods. A series of factorial experiments was carried out on 12 existing runoff plots. The study commenced in 1996 after a 5-year natural fallow. Mound tillage was introduced in 1997 till 1999. The legumes - Vigna unguiculata (cowpea), Mucuna pruriens and Pueraria phaseoloides - were intercropped with maize in 1996 and 1998 while yam was planted alone in 1997 and 1999. This paper covers 1997-1999. At the end of each year, residues were either burned or mulched on respective plots. Soil loss, runoff, variations in mound height, bulk density, soil water retention and sorptivity were measured. Cumulative runoff was similar among interactions of legume and residue management in 1997 (57-151 mm) and 1999 (206-397 mm). However, in 1998, cumulative runoff of 95 mm observed for Mucuna-burned residue was significantly greater than the 46 mm observed for cowpea-burned residue and the 39-51 mm observed for mulched residues of cowpea, Mucuna and Pueraria. Cumulative soil loss of 7.6 Mg ha(-1) observed for Mucuna-burned residue in 1997 was significantly greater than those for Pueraria-mulched (0.9 Mg ha(-1)) and Mucuna-mulched (1.4 Mg ha(-1)) residues whereas in 1999 it was similar to soil loss from cowpea treatments and Pueraria-burned residue (2.3-5.3 Mg ha(-1)). There were no significant differences in soil loss in 1998 (1-3.2 Mg ha(-1)) whereas Mucuna-burned residue had a greater soil loss (28.6 Mg ha(-1)) than mulched cowpea (6.9 Mg ha(-1)) and Pueraria (5.4 Ms ha(-1)). Mound heights (23 cm average) decreased non-linearly with cumulative rainfall. A cumulative rainfall of 500 mm removed 0.3-2.3 cm of soil from mounds in 1997, 3.5-6.9 cm in 1998 and 2.3-4.6 cm in 1999, indicating that (detached but less transported) soil from mounds was far higher than observed soil loss in each year. Soil water retention was improved at potentials ranging from -1 to -1500 kPa by Mucuna-mulched residue compared to the various burned-residue treatments. Also, mound sorptivity at -1 cm water head (14.3 cm h(-1/2)) was higher than furrow sorptivity (8.5 cm h(-1/2)), indicating differences in hydraulic characteristics between mound and furrow. Pueraria-mulched residues for mounds had the highest sorptivity of 17.24 cm h(-1/2), whereas the least value of 6.96 cm h(-1/2) was observed in furrow of Mucuna-burned residue. Pueraria phas eoloides was considered the best option for soil conservation on the previously eroded soil, cultivated with mound tillage.

Salako, F. K., G. Tian, G. Kirchhof and G. E. Akinbola (2006). Soil particles in agricultural landscapes of a derived savanna in southwestern Nigeria and implications for selected soil properties. Geoderma 137(1-2): 90-99.

The vast area of savanna ecology in Afiica plays a significant role in food production, making a study of soils in this zone very important. Therefore, soil physical and chemical properties of 14 soil profiles were studied in a derived savanna zone of southwestern Nigeria on 2 toposequences at 2 locations (Ibadan and Alabata), which were 20 kin apart. Six soil profiles were studied at Ibadan while 8 were studied at Alabata. Morphological descriptions of profiles were carried out. Data collected included particle size distribution, bulk density, clay dispersion, water retention characteristics, pH, organic carbon, exchangeable K, Ca, Mg and available P. Soil profiles along the toposequences were well-developed with depths exceeding 180 cm, except for one profile at the lower slope position where an indurated plinthic layer was found at 68 cm depth. The horizons were easily distinguished with color, texture and consistency. Total sand, with the main component being coarse sand, decreased with depth from 813 to 502 g kg(-1) at Ibadan and from 824 to 635 g kg(-1) at Alabata. The clay content increased with depth from 54 to 3 5 6 g kg(-1) at Ibadan and from 63 to 279 g kg(-1) at Alabata. Gravel concentration was highest for soil horizons found between 20 and 102 cm depth. Also, bulk density increased with soil depth from 1.35 to 1.51 g cm(-3) at Ibadan and from 1.38 to 1.64 g cm(-3) at Alabata, indicating that subsoil horizons were more compact due to higher clay and gravel contents, and sticky consistency. The A horizon had a significantly higher water content at water potentials > 2 kPa while the subsoils had higher water content at

Kirchhof G., So H.B. (2005). Rice Growth and Post-Rice Mungbean in Relation to Two Puddling Intensities under Glasshouse conditions. Australian Journal of Soil Research, 43, 623-628.

The effect of soil puddling on growth of lowland rice (Oryza sativa) and post-rice mungbean (Vigna radiata) was investigated using mini rice beds under controlled glasshouse conditions. Each mini rice bed was approximately 1 m3in size. Three different soil types were used: a well-drained, permeable loam; a hardsetting, structurally unstable silty loam; and a medium clay. Rice yields were reduced by low puddling compared with high puddling intensity on the loam but not affected on the heavier textured soils (silty loam and clay). Yield of mungbean was reduced on highly puddle, structurally unstable soil, indicating that puddling should be reduced on structurally unstable soils. Under glasshouse condition where crop establishment was not a limiting factor and plant available water in 0.65 m of soil was 100 mm, mungbean yields of >1 t/ha were achieved. However, under conditions where subsoil water reserves were depleted for the production of vegetative biomass during initial optimal growing condition, grain yield remained well below 1 t/ha.

Kirchhof G., So H.B. (2005). Soil Puddling for Rice Production under Glasshouse Conditions - Its Quantification and Effect on Soil Physical Properties. Australian Journal of Soil Research, 43, 617-622

The effect of soil puddling on soil physical properties of 3 different textured soils (clay, loam, and silty loam) and growth of rice (Oryza sativa) on these soils was investigated under glasshouse conditions. Puddling intensity was expressed as the ratio of soil volume subjected to the puddling implement and the total soil volume in the puddled layer, thus integrating the effects of speed and time of the puddling operation. This parameter was well related to soil dispersion, bulk density, and saturated hydraulic conductivity. However, following prolonged periods of submerged conditions during rice growth, saturated hydraulic conductivity decreased with a decrease in soil dispersion, in contrast to an expected reduction in saturated hydraulic conductivity with increased dispersion. There was indication that continuous waterlogging reduced the effect of soil puddling, in particular on heavy-textured soils.

Loetscher T, Dart P, Kirchhof G, Gray S (2005). Naiad: Sharing Lessons Learned from Innovative Urban Water Schemes. AWA Water Journal, September 2005, 60-62.

There are now numbers of innovative water projects in Australia, already implemented and planned, that serve as a testing ground for new technologies, management approaches and institutional frameworks, generating valuable experience and insights. To date, this knowledge is largely shared in an opportunistic, uncoordinated fashion. As a result, planners and practitioners alike often find it difficult to gain access to information about existing innovative water schemes and projects that could benefit the development of their own project. The Naiad project aims to change this by developing a computer program for sharing lessons learned from urban water schemes among planners, local governments, and practitioners. The project is a component of the Sustainable Water Sources program of the CRC for Water Quality and Treatment, which is carried out at The University of Queensland in collaboration with CSIRO. A preliminary version of Naiad has recently been completed. The current project stage focuses on populating its knowledge base with interesting stories about innovative water schemes.

Loetscher T, Gray S, Kirchhof G, Dart P (2005). Naiad: Sharing Lessons Learned from Innovative Urban Water Schemes. Proceedings, Australian Water Association, Ozwater Conference, Brisbane, 8-12 May 2005.

The Naiad project is a component of the Sustainable Water Sources program of the CRC for Water Quality and Treatment, which is carried out at The University of Queensland in collaboration with CSIRO. Its aim is to develop a computer program for sharing lessons learned from innovative urban water schemes among planners, local governments, and practitioners. The 2002-2003 drought, continued strong population growth in urban centres, and record low water storage levels have made sustainable water management a national priority. A paradigm shift toward water recycling and source substitution has led planners and practitioners to look for alternative solutions. Consequently, the Australian water sector is rapidly developing into a large community of practice (CoP), where sharing information and lessons learned is a key driver of innovation. There now are a number of interesting projects, already implemented and planned, that serve as a testing ground for new technologies, management approaches and institutional frameworks, generating valuable experience and insights. To date, this knowledge is largely shared in an opportunistic, uncoordinated fashion. As a result, planners and practitioners alike often find it difficult to gain access to information about existing innovative water schemes and projects that could benefit the development of their own project. This paper discusses the importance of formalising and facilitating an Australian CoP toward effectively sharing knowledge about and thereby furthering innovative water management, and it establishes the role of a tool such as Naiad in supporting this CoP. Once completed, Naiad will be a convenient interactive knowledge pool about innovative water schemes. Users will be able to query its comprehensive database with respect to a range of search criteria such as source type, type of water (re-)use, capacity, and objectives (source substitution, cost reduction, etc.). Naiad will identify schemes that match the query and display detailed information about these schemes, including treatment technologies used, cost, O&M regime, institutional framework, stakeholder consultation, risk management approach, and lessons learned. It will also include a library of guidelines and standards, and allow viewing of multimedia files, including video footage, about selected schemes. A prototype version of Naiad is currently nearing completion. This paper will present this prototype and use a case study to illustrate the type of information that will be contained in its database.

Bakti L.A.A., So H.B.; Kirchhof G. and Yatapanage K. (2003). Structural Regeneration of Puddled Soil. Proceedings, International Soil Tillage Research Organisation, 16th Triennial Conference: Soil Management for Sustainability 13–18 July 2003, The University of Queensland - Brisbane – Australia. CDrom, 59-63.

Kirchhof G. and Daniel H. (2003). A technique to assess small scale heterogeneity of chemical properties in soil aggregates. Australian Journal of Soil Research. 41, 919-932

A new method is presented which allows the separation of the soil aggregate exterior from the aggregate core. The method employs a combination of aggregate freezing with rapid separation of aggregate exteriors using ultrasonic energy. The factors influencing the thickness of the removed aggregate surface layer include water content of the aggregate prior to freezing, temperature difference between that of the frozen aggregate and that of the liquid it is submerged in during sonification, sonification time and energy, and the type of the immersion liquid. The success of the method and the thickness of the removed aggregate surface were examined using barium (Ba2+) as a tracer. Barium (as BaCl2) is rapidly absorbed by soil and is present at only very low levels in natural soils. Surface layers of 0.2–0.4 cm thickness were successfully removed from aggregates of 1–4 cm diameter. Two examples are given from soils in northern NSW to demonstrate the occurrence of small-scale hetero-geneity in soil chemical properties. Compared with the surface fraction, a 4–7% higher calcium concentration was found in the core fraction of a clay loam soil (Dermosol). Conversely, on a cracking clay soil (Vertosol), atrazine concentration was around 15 times greater in the aggregate surface fractions compared with core fractions. Compared with the traditional estimation of soil chemical properties on homogenised bulk soil samples, it is suggested that separate analysis of aggregate surface and core fractions could provide useful additional information on the relationships between soil properties and environmental responses.

Kirchhof G., and Daniells I. (2003). Soil Management Practices in Northern New South Wales Proceedings, International Soil Tillage Research Organisation, 16th Triennial Conference: Soil Management for Sustainability 13–18 July 2003, The University of Queensland - Brisbane – Australia. CDrom, 626-631.

Salako F.K. and Kirchhof G. (2003). Field hydraulic properties of an Alfisol under various fallow systems in southwestern Nigeria. Soil Use and Management. 19, 340-346.

The effects of various fallow management systems and cropping intensities on water infltration were measured on an Alfisol at Ibadan in southwestern Nigeria. The objective was to determine the influence of the land use systems (a combination of crop±fallow sequences and intercropping types) on soil hydraulic properties obtained by disc permeameter and double-ring infiltration measurements. The experiment was established in 1989 as a split-plot design with four replications. The main plots were natural fallow, planted Pueraria phaseoloides and planted Leucaena leucocephala. The subplots were 1 year of maize/cassava intercrop followed by 3-year fallow (25% cropping intensity), or 2-year fallow (33% cropping intensity), or 1-year fallow (50% cropping intensity), or no fallow period (100% cropping intensity). Water infiltration rates and sorptivities were measured under saturated and unsaturated flow. Irrespective of land use, infiltration rates at the soil surface (121±324 cm h±1) were greater than those measured at 30 cm depth (55±144 cm h±1). This indicated that fewer large pores were present below 30 cm depth compared with 0±30 cm depth. Despite some temporal variation, sorptivities with the highest mean value of 93.5 cm h-1 increased as the cropping intensity decreased, suggesting a more continuous macropore system under less intensive land use systems. This was most likely due to continuous biopores created by perennial vegetation under long fallow systems. Intercropped maize and cassava yields also increased as cropping intensity decreased. The weak relationship between crop yields and hydraulic conductivity/infiltration rates suggests that the rates were not limiting.

Salako, F. K. and G. Kirchhof (2003). Field hydraulic properties of an Alfisol under various fallow systems in southwestern Nigeria. Soil Use and Management 19(4): 340-346.

The effects of various fallow management systems and cropping intensities on water infiltration were measured on an Alfisol at Ibadan in southwestern Nigeria. The objective was to determine the influence of the land use systems (a combination of crop-fallow sequences and intercropping types) on soil hydraulic properties obtained by disc permeameter and double-ring infiltration measurements. The experiment was established in 1989 as a split-plot design with four replications. The main plots were natural fallow, planted Pueraria phaseoloides and planted Leucaena leucocephala. The subplots were 1 year of maize/cassava intercrop followed by 3-year fallow (25% cropping intensity), or 2-year fallow (33% cropping intensity), or 1-year fallow (50% cropping intensity), or no fallow period (100% cropping intensity). Water infiltration rates and sorptivities were measured under saturated and unsaturated flow. Irrespective of land use, infiltration rates at the soil surface (121-324 cm h(-1)) were greater than those measured at 30 cm depth (55-144 cm h(-1)). This indicated that fewer large pores were present below 30 cm depth compared with 0-30 cm, depth. Despite some temporal variation, sorptivities with the highest mean value of 93.5 cm h(-1/2) increased as the cropping intensity decreased, suggesting a more continuous macropore system under less intensive land use systems. This was most likely due to continuous biopores created by perennial vegetation under long fallow systems. Intercropped maize and cassava yields also increased as cropping intensity decreased. The weak relationship between crop yields and hydraulic conductivity/infiltration rates suggests that the rates were not limiting.

Shelton M, Kirchhof G, Emmery P, Shehan W, Rowlings D, Poole H, Budisantoso E (2003). Leucaena as an opportunity for recharge management in northern Australia: Fitzroy Basin Case Study. 9th PUR$L National Conference (Productive Use and Rehabilitation of Saline Lands), Yeppoon Qld, 29th September to 2nd October 2003.

A revegetation strategy to prevent dryland salinity and improve water quality is proposed for the Fitzroy Basin Catchment based on planting of the perennial forage tree legume leucaena for cattle production. Scientific and grazier evidence from studies in Queensland and overseas indicates that leucaena will be effective in reducing deep drainage and runoff. Rooting depth and water use measurements are reported which indicate that leucaena will mimic the original native perennial woody vegetation. The strategy is being developed by the Leucaena Network, a grazier-based organization, in consultation with community, industry, and Government organizations. The weedy aspect of leucaena is acknowledged and is addressed by a Code of Practice for planting and management of leucaena to ensure that graziers are responsible for any weed leucaena outbreaks that occur as a result of the plantings. Direct economic benefits to the Fitzroy region from planting 250,000 ha of leucaena will be an additional 15-20,000 tonnes of beef produced per year with an internal rate of return of 28.8-38.6% to the grazier, for a total annual benefit of $7.5-15 million. Indirect economic benefits will accrue from dryland salinity risk reduction, improvement in water quality, significant amounts of carbon sequestered per year, and the cycling of biologically fixed nitrogen.

Danesh M., Daniel H. and Kirchhof G. (2002) The impact of long term crop rotations and residue management on physical properties of a northern NSW black earth (Vertosol). ASSSI National Soils Conference – Future Soils, Perth 2-6 December 2002. p50.

Warialda (along with 4 other regional sites) was selected as part of a large scale no-tillage research trial in 1981 to be representative of the major soil types for wheat production in the 600-700 mm annual precipitation range in northern N.S.W. This here presented associated study, undertaken at a time near the closure of the large no-tillage research trial, looks at the effects of different long-term (more than 20 years) crop rotations and different tillage treatments on soil physical properties that were conducted at Warialda at the University of New England McMasters Field Station. Crop rotation treatments included were A: continues wheat, C: 3 year rotation E: 2 year rotation (wheat/fababean), G: (wheat/barley/fababean). Tillage treatments included were no-tillage fallow (NT), cultivated fallow with the stubble burnt (SB) and cultivated fallow with the stubble retained (SR). Soil physical properties measured were infiltration rate, aggregate stability and total carbon content. Although several studies have been conducted in the past to evaluate the long-term effects of this type of treatments on soil physical properties, the conclusions given from those are often inconsistent. The long duration of the period of treatments in this report eliminates one of the main factors contributing to this, which is the shorter duration of previous studies.

Kirchhof G., Johnson I. and Daniel H. (2002). Variability of deep drainage - paddock leakiness hot spot. ASSSI National Soils Conference – Future Soils, 2-6 December Perth 2002. p88.

Dryland salinity is a major threat to future agricultural production in Australia. The main cause of salinisation is attributed to a change in landscape hydrology whereby water use efficient native vegetation has been replaced by less water use efficient crops or pastures (CoA 2001). Due to this change in water balance, the excess water is thought to lead to recharge of groundwater resulting in upward mobilisation of cyclic salts that were deposited into the landscape from rainfall during the past 2-3 million years (CoA 2001). Evaluation of water balances on a paddock scale generally assumes diffuse recharge. This implies that the paddock’s soil hydraulic properties can simply be described as single values varying vertically but not horizontally. Models such as SWIM or APSIM can then be employed to test under what combinations of land use and climate, recharge (=deep drainage) is minimal (Ringrose-Voase et al 2001). Resulting recommendations may include the often-advocated large-scale tree plantations to remedy dryland salinity (CoA 2001). Variation of paddock hydraulic properties is ignored although there is general acknowledgment that leakiness may vary within paddocks. The variation of this leakiness has previously not been quantified.

Soil Health Seminar – keeping our soils alive (2002). Ed. G. Kirchhof. Proceeding, Ashford 20th Feb, Lake Keepit 21st Feb. 2002. ISBN 07347 1344 4. NSW Agriculture. 182p.

Foreword: There’s an old Chinese proverb that says ‘Soil is the Mother of all Things’. Soil will always be the foundation of life. This has been a well-recognised fact until the beginning of the green revolution when we began to treat soil as a chemical reactor that needed little more than mineral fertiliser to be productive. Our life in this century focuses more and more around economic benefits, high tech machinery and microchips – and we have to relearn that we cannot reduce soil to lifeless dirt if we want to maintain our lifestyles. This is now often termed the double-green revolution, when we recognise that soil is alive and in fact the largest living organism on earth. Soil, at first sight is perhaps not as pretty and colourful as the second largest living organism, the Great Barrier Reef, but if we look closer we will discover an intimate and tremendously complex array of interconnected organisms coexisting and working within a bio-chemical environment. Professor John Doran, a renowned soil scientist from the University of Nebraska, pointed out in 1996 that there are more than 10,000 different organisms in each gram of soil and each teaspoon contains more than 1.5 times more individual organisms than there are people on earth. Aluminium is one of the major elements present in our soil and also one of the most toxic for animal and plant life. If around three grams of aluminium per cubic meter of soil is soluble, it is toxic to plants, but our soils on average contain around 70 kg per cubic meter! A functioning healthy soil system will prevent massive aluminium toxication. The production of food requires large quantities of water. For example, the grain required to produce a loaf of bread needs about 250 litres of water. If we were to untangle all visible roots to 1 meter depth in one hectare of our soils, the string would easily cover the circumference of our planet. A healthy soil will allow roots to thrive, and is easily able to supply the roots with large amounts of water. These are only a few of the fascinating accomplishments of our soil. The terms ‘soil health’ or ‘soil quality’ are increasingly being used to describe ‘the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation’ (Soil Science Society of America, Glossary 1998). For the farmer this simply means the suitability of the soil to continue to support crop growth and pasture without resulting in soil degradation or harming the environment. There is no general panacea to manage our soils. Understanding our soils is the foundation for the adoption of management practices that will maintain soil health and quality. In this seminar we will discuss soil processes with you that will put you in a position to decide on soil husbandry practices that maintain healthy soil.

Soil Health Seminar – keeping our soils alive (2002). Soil structure – the living space of our soils. Ed. G.Kirchhof. Proceeding, Ashford 20th Feb, Lake Keepit 21st Feb. 2002. ISBN 07347 1344 4. NSW Agriculture. p 161-182.

Kirchhof G. (2001). Plastic Properties. In: Encyclopaedia of Soil Science. Editor: Rattan Lal. Invited contribution, Marcel Dekker Inc.

Application of a force to soil can result in an elastic, non-permanent, deformation that only lasts while the force is applied, or a plastic, permanent deformation that persists after the load is removed. The latter may or may not result in a decrease in the soil volume. How easily and how much the volume changes is determined by the soil’s plasticity. It is an important factor influencing ease and outcome of soil tillage operations. Soil plasticity is caused by the lubricating film of water surrounding soil particles that allows the soil to change shape without rupturing upon application of forces. As an inherent soil property, it is governed primarily by the surface area of the soil particles. Plasticity increases with increasing clay content, activity of clay minerals, position of the adsorbed cations in the lyotropic series, and organic matter content.

Kirchhof G. (2001). Soil physical analysis of the core sites. In: Edwards J. Ed, WFS Results book 2nd edition. GRDC project DAN 266. NSW Agriculture Orange.

Kirchhof G. and Daniells I. (2001). Soil Structure – the key the key to sustainable agro-ecosystem management. In: Soil Health - The foundation of sustainable agriculture. Ed: R.Lines-Kelly. Wollongbar, NSW, Australia, 97-103.

So H.B, Kirchhof G., Bakker R. and Smith G.D. (2001). Low Input Tillage/Cropping Systems for Limited Resource Areas. Soil and Tillage Research. 61, 109-123.

Agriculture in limited resource areas is characterized by small farms which are generally too small to adequately support the needs of an average farm family. The farming operation can be described as a low input cropping system with the main energy source being manual labor, draught animals and in some areas hand tractors. These farming systems are the most important contributor to the national economy of many developing countries. The role of tillage is similar in dryland agricultural systems in both the high input (HICS) and low input cropping systems (LICS), however, wet cultivation or puddling is unique to lowland rice-based systems in low input cropping systems. Evidence suggest that tillage may result in marginal increases in crop yield in the short term, however, in the longer term it may be neutral or give rise to yield decreases associated with soil structural degradation. On marginal soils, tillage may be required to prepare suitable seedbeds or to release adequate Nitrogen through mineralization, but in the longer term, however, tillage reduces soil organic matter content, increases soil erodibility and the emission of greenhouse gases. Tillage in low input cropping systems involves a very large proportion of the population and any changes in current practices such as increased mechanization will have a large social impact such as increased unemployment and increasing feminization of poverty, as mechanization may actually reduce jobs for women. Rapid mechanization is likely to result in failures, but slower change, accompanied by measures to provide alternative rural employment, might be beneficial. Agriculture in limited resource areas must produce the food and fiber needs of their community, and its future depends on the development of sustainable tillage/cropping systems that are suitable for the soil and climatic conditions. These should be based on sound biophysical principles and meet the needs of and be acceptable to the farming communities. Some of the principle requirements for a sustainable system includes the maintenance of soil health, an increase in the rain water use efficiency of the system, increased use of fertilizer and the prevention of erosion. The maintenance of crop residues on the surface is paramount for meeting these requirements, and the competing use of crop residues must be met from other sources. These requirements can be met within a zonal tillage system combined with suitable agroforestry, which will reduce the need for crop residues. It is, however, essential that farmers participate in the development of any new technologies to ensure adoption of the new system.

Jayawardane, N., Kirchhof, G., Blackwell, J. (2000). Soil Slotting to ameliorate subsoil limitations to crop production. Proceedings, "Tillage at the Threshold of the 21st Century: Looking Ahead", 5th Conference of the International Soil Tillage Research Organisation (ISTRO). Fort Worth, Texas, USA, 2-7 July 2000.

Subsoil amelioration by soil slotting involves partial or segmental subsoil loosening, using rotary blades to dig trenches into the soil, similar to those created with chain type trenchers e.g.; ditch witches. These trenches, or slots are up to 100 cm deep and usually around 15 cm wide. The excavated soil is backfilled into the slots, with or without added ameliorants (gypsum, lime, fertilizer, trace elements, sludge etc…). Distance between slots depends on soil amelioration requirements, but slots are generally 1 or 2 m apart, and, if necessary crosshatched. Gypsum-slotting of sodic and slowly permeable soils improves crop production by improving soil aeration in surface layers and increasing water storage in deeper layers. Lime-slotting on acid subsoil results in greater root development to depth, and hence increased water extraction. Unlike subsoil loosening through deep ripping, slots are more resilient to re-compaction as the undisturbed soil between slots protects the loose soil from repacking during high overburden loading and wheeling. This greatly improves the longevity of the tillage effects. An important advantage of slotting over deep ripping is that soil ameliorants can be easily added to the slot and are thoroughly mixed with the soil in the slot. Incorporation of sewage sludge to depth is possible at very high rates (350 t/ha) with minimum environmental effects caused by surface runoff and erosion of the added sewage sludge. Due to the high N and P content, soil fertility of sludge-enriched slots has a dramatic effect on crop yields (300% on Barley). The organic component of the sludge can also stabilize the structure within the slot through buildup of organic matter. Water movement through the network of slots in a paddock is rapid, but waterlogging inside the slots can occur if outflow from the slots is limited and subsoil hydraulic conductivity of the non-slotted soil is low. Although slotting has been proven to provide amelioration for a range of subsoil constraints adoption at present is low, and is only economic on high value horticultural crops.

Kirchhof G. , H.B. So, T. Adisarwanto, W. H. Utomo, S. Priyono, B. Prastowo, M. Basir, T.M. Lando, Subandi, E.V. Dacanay, D. Tan-Elicano and W.B. Sanidad (2000). Growth and Yield response of Legume Crops to different Soil Management Practises after Rainfed Lowland Rice. Soil and Tillage research. 56, 51-66.

Field experiments were conducted over a 3-year period (1992–1995) in Sulawesi, East Java and the Philippines to investigate the response of post-rice (Oryza sativa L.) soil managements on growth and yield of legumes after lowland rice under rainfed conditions. Grain legume yields ranged from complete crop loss due to excessive rainfall after sowing to a maximum of 1.08 Mg ha-1 for mungbean (Vigna radiata (L.) Wilzek), 1.33 Mg ha-1 for soybean (Glycine max L. Merr.) and 2.3 Mg ha-1 for peanut (Aracis hypogaea L.). The response and magnitude of the effects from different management systems on legumes were closely related to the climatic conditions prevailing during the crop establishment phase. Correct timing of legume sowing was seen as the most important factor determining successful moderate crop production, followed by the availability of subsoil water reserves. Tillage was considered a potential method to improve yields because sowing could be carried out later during the dry season when rainfall was more predictable. Tillage, provided it is carried out at suitable soil water contents, could probably partially overcome the adverse soil physical condition induced during the rice phase. Fertiliser application tended to increase food legume in wetter areas showing that residual fertiliser effects from the previous rice crop could be limiting. In drier areas, fertiliser application had little effect on grain legume yields. Mulch as a soil amendment tended to increase yields in drier areas due to its water conservation effect. In wetter areas mulching was not necessary and could even lead to yield reduction if conditions were too wet.

Kirchhof G., S. Priyono, W. H. Utomo., T. Adisarwanto, E.V. Dacanay and H.B. So (2000). The Effect of Soil Puddling on the Soil Physical Properties and the Growth of Rice and Post-Rice Crops. Soil and Tillage Research. 56, 37-50.

Changes in soil physical properties due to traditional methods of puddling for lowland rice (Oryza sativa L.) production and post-rice legumes was investigated in field experiments conducted on three sites in Indonesia and two in the Philippines over a 3-year period. Puddling treatments used in the field were, in increasing order of puddling intensity, dry cultivation prior to submergence, one and two plowing and harrowing treatments using a draught animal and associated implements, and two cultivations using a mechanical roto tiller. Rice was followed by mungbean (Vigna radiata (L.) Wilzek) on all five sites, and in addition soybean (Glycine max L. Merr.) at Ngale and peanut (Aracis hypogaea L.) at Jambegede were also grown. All puddling treatments were followed by post-rice treatments of surface drainage (with and without surface drains) for the Indonesian sites and sowing technique (zero-till-dibble versus plough-broadcast-harrow) for the Philippine sites. Rice yields were highest under the traditional puddling techniques using draught animal traction. Results suggested that puddling with a roto tiller reduced yield because of insufficient depth of puddling, while dry cultivation may have reduced yield due to increased soil strength of the puddled layer; both are thought to limit root development. Puddling had no significant effect on post-rice mungbean and peanut production. However, results showed that increasing puddling intensity tended to reduce soybean yield. Dry cultivation of lighter textured, well drained soils such as at Manaoag, tended to require more intensive weed control in both rice and dryseason crops compared to higher puddled treatments. Weed infestation was thought to be the largest contributing factor for reduced mungbean yield at Manaoag. Increasing soil puddling intensity at Ngale and Jambegede appeared to reduce root growth. Soil water depletion tended to be smaller in the plough layer that was cultivated under wet conditions compared to pre-rice dry land preparation. Soil water extraction was small and root proliferation was up to 40 cm depth under wet conditions where plant water requirements were met from seasonal rainfall. Root proliferation was deeper and soil water use greater under dry climatological conditions. Small amounts of subsoil water use resulted in substantial yield increases ranging from 3–24 kg mm-1 of soil water used, reinforcing the important role of subsoil water storage and use by the dry season crop in this farming system.

Kirchhof, G., Daniells, I., Schwenke, G. (2000). Changing tillage methods and their effect on soil structure on major dryland cropping soils in North Western New South Wales, Australia. Proceedings, "Tillage at the Threshold of the 21st Century: Looking Ahead", 5th Conference of the International Soil Tillage Research Organisation (ISTRO). Fort Worth, Texas, USA, 2-7 July 2000.

Long term sustainability of dryland cropping in north western New South Wales (Australia) requires quality soil structure to maximise water storage and root exploration and minimise soil erosion. Soil structural decline under cropping is a well-recognised problem in this agro-ecosystem. Although there are many causes of structural decline, excessive or inappropriate tillage are major contributing factors. Soil structural decline is manifested in reduced aggregate stability, reduced macro-porosity with concomitant decreased water infiltration and increased erosion, and topsoil loss with associated exposure of sodic subsoil layers on some soils. During the past decade, the farming community has become increasingly aware of these problems. With the advent of low-cost herbicides more farmers are switching from conventional tillage to conservation or reduced tillage systems. Although research has demonstrated that conservation tillage (minimum or zero tillage) is potentially more economically and environmentally sustainable than conventional tillage (multiple cultivation operations using tyned or disked implements), it is still unclear what influence the change to conservation tillage has on soil structure in farmers fields. The objective of this study was to evaluate if changing tillage methods affect soil structural indicators on commercial dryland farms in north-western New South Wales, Australia. We inspected 40 randomly selected dryland cropping farms in north-western New South Wales to evaluate the effect of soil management practices on soil structure. Three sites were selected at each farm; two cropped sites and a never-cultivated control. Soil structural indicators measured were hydraulic properties, soil organic matter and exchangeable cations. Hydraulic conductivities at high matric potentials (-3.5 to -1.5 cm suction) were measured in situ using disc permeameters. Saturated hydraulic conductivity was measured in the laboratory on undisturbed core samples, 10 cm diameter and 7 cm height. They were taken at 3 to 10 cm and 18 to 25 cm depth. Disturbed samples were collected from corresponding depths for analysis of chemical soil analysis. Farmer’s records or recollections were used to categorise the fields according to past (more than 3 years ago) and current (the last 3 years) tillage methods. The broad categories for tillage method were conventional tillage and conservation tillage. broad categories for tillage method were conventional tillage and conservation tillage. The soil types observed on the farms were Black Earth (32% of fields surveyed), Brown Clay (15%), Duplex Soils (8%), Gradational Soils (15%) and Grey Clay (31%). Using international taxonomy, the Duplex Soils in this study tend to fall under planosols, the Gradational Soils under luvisols and candisols, the Grey and Brown Clays under chromic vertisols, and the Black Earths under pellic vertisols. On the majority of the fields (67%) conventional tillage was and still is practiced. Conservation tillage was taken up on 21% of the fields. On 10% of the fields (1/3on Black Earths and2/3 on Grey Clays) conservation tillage has always been practiced. These were all fields that were brought into cropping within the last 10 years. Fields converted to conservation tillage were all on swelling clay soils, mostly Black Earths and Brown Clays and, to a smaller extent, on the Grey Clays. Except on the Grey Clays we could not detect a significant increase in unsaturated hydraulic conductivity due to the change from conventional to conservation tillage. We observed that unsaturated hydraulic conductivity on the Grey and Brown Clays tended to be higher on the cultivated fields compared to the controls. Soil structural decline due to cultivation was most evident on the Black Earths. Saturated hydraulic conductivities of the always conventionally cultivated fields was smaller than those of the control sites, but increased when conservation tillage was adopted. Sites where conservation tillage was always practiced had the highest saturated conductivities on these soils. Soil organic carbon on the control sites was always greater than the corresponding cultivated sites regardless of whether conventional or conservation tillage was practiced. Cation exchange capacities and exchangeable sodium percentages were largely unaffected by cropping and tillage practices on the different soil types assessed in this study Of the soil types surveyed in this study, we concluded that Black Earths are most responsive to the adoption of conservation tillage. Compared to the other main soil types they are more resilient to soil structural decline due to their strong shrink-swell properties. Prolonged practice of conservation tillage on the other soil types may be required before benefits to soil structure can be observed under continuous cropping systems of this region. The results of this study also question whether cultivated soils under cropping necessarily always have inferior structure, besides lower soil organic matter, compared to never cultivated soils of this region.

Kirchhof, G., Salako F.K. (2000). Residual tillage and bush-fallow effects on soil properties and maize intercropped with legumes on a tropical Alfisol. Soil Use and Management. 16, 183-188.

After six years of bush-fallow, residual effects on soil productivity of tillage practices prior to the fallow were investigated on an Alfisol in southwestern Nigeria. In 1996 fallow was followed by maize intercropped with cover crops of Pueraria phaseoloides, Mucuna pruriens or cowpea (Vigna unguiculata) and no intercrop. Parameters measured included soil properties, ground cover, crop growth and yield, rainfall erosivity, runoff and soil loss. In spite of six-years of bush-fallow and establishment of cover crops, soil erosion was significantly greater on plots that had been conventionally cultivated previously using disc ploughs, harrows and mechanical rotovators (1.78 t ha71season71) compared to previously no-till plots (1.34 t ha-1season-1). Crop growth and yields were least and soil loss greatest (2.83 t ha-1season-1) on the previous bare plot. Maize grain yield was highest using Pueraria phaseoloides as an intercrop (2.15 t ha-1) followed by a cowpea inter-crop (1.92 t ha-1), maize without intercrop (1.87 t ha-1) and Mucuna pruriens intercrop (1.71 t ha-1). The maize grain yields reflected levels of competition from the cover crops. Cowpea-maize intercrop may be most suitable for farmers because maize yields were satisfactory and cowpea grain serves as additional subsistence. Cowpea yields were 390 kg ha-1. Soil erosion was also moderate using cowpea as an intercrop (1.71 t ha-1season-1). However, Pueraria phaseoloides gave the best erosion control with a soil loss of 1.34 t ha-1 season-1

Kirchhof, G., Smith, P., Hyson L. (2000). Variation in plant available water and hydraulic conductivity along transects of different textured soils. Proceedings, 5th International Conference on Precision Agriculture. July 16-19, 2000. Precision Agriculture Centre, Univ. of Minnesota, USA.

Many irrigation practices in Australia are still based on the assumption that irrigation water is plentiful and non-limiting. This has led to inefficient irrigation management with concomitant environmental problems such as increased salinity, unacceptable reduction in environmental flow and sub-optimum yields caused by over- and under irrigation. Efficient irrigation requires that land users be provided with data on plant available and readily available water. Little consistent soil information is currently available that can be used by the practitioner to optimize irrigation scheduling. Hydraulic conductivities, texture, soil water release characteristic and soil strengths were measured at 4 different depths at 5 to 7 locations along a 5 m transect on a heavy clay under irrigated cotton, and a silty clay and a silty clay loam under pasture. The results from this pilot study clearly showed that irrigation parameters, such as total and readily plant available water recommended on texture class alone are inadequate for efficient irrigation design. Variation in readily available water was greater than that of total plant available water due to the influence of soil structure at soil water contents at matric potential higher than permanent wilting point. Variation within the soil profile was greater than across the transect due to the influence of soil depth, in particular the effect of overburden pressure in swelling clay soils. However, permanent wilting point was closely related to clay content irrespective of clay type. Hydraulic conductivity underneath permanent tracks in a controlled traffic systems showed that compaction had spread laterally into the subsoil.

Rahmianna A., Sanidad W.B., Adisarwanto T., Kirchhof G. and So H.B. (2000). Crop establishment of legumes in rainfed lowland rice-based cropping systems. Soil and Tillage research. 56, 67-82.

Poor crop establishment is one of the major limitations to the production of grain legumes after rice (Oryza sativa L.) in rainfed lowland rice-based cropping systems. The success of germination and emergence of mungbean (Vigna radiata (L.) Wilzek), soybean (Glycine max (L.) Merr) and peanut (Arachis hypogaea L.) planted in zero tilled (ZT), zero tilled combined with mulch application (ZTM) and tilled soils (T) were investigated in a crop establishment trial as a function of sowing delay. Sowing delay was used as a surrogate for soil-water content. This experiment was conducted under a rain-shelter to ensure continuous and progressive drying conditions. A dibbling trial using the same legumes was conducted concurrently and subjected to the prevailing climatic conditions. Germination and emergence success rate of the traditional dibbling method was compared to dibbling incorporating depth control and seed cover. Both experiments were conducted towards the end of the 1994 rainy season in a Vertisol soil at Ngale and an Andosol soil at Jambegede, in East Java, Indonesia where the season gradually changes from wet to dry season. Mungbean emergence was 93–94% at Ngale and soybean emergence was 84–95% at Jambegede, both in the presence and absence of rain. Peanut emergence was low (50–69%) at both sites. In all three species at both sites, the percentage of seeds that failed to germinate was greater than seeds that failed to emerge, indicating that germination rather than emergence was limiting. Seed rot caused by fungal attack and poor imbibition associated with poor seed–soil contact (observed as intact seeds) were the main constraints for the success of germination of mungbean, soybean and peanut. The failure to emerge was mainly caused by seedling rot and the failure of hypocotyl and radicle to penetrate the hard soil, observed as a curling of the hypocotyl. Cultivation at Ngale on a Vertisol resulted in excessively cloddy soil, which in turn resulted in a significant decrease in germination and emergence. The application of straw mulch had little effect on the emergence of legumes on this soil. The use of depth control and application of seed–soil cover did not have a significant effect. Hence the traditional dibbling method where depth of planting ranged from 4 to 7 cm without seed cover was found to be appropriate for planting mungbean and soybean. Germination and emergence of peanut was improved with the application of soil cover and the dibbling stick had a spike added to the tip to assist the root to penetrate the hard compacted soil.

Salako, F.K., Kirchhof, G., Tian, G. (2000). Conservation of a tropical Alfisol using legume cover crop intercropping and residue mulch. Proceedings, "Tillage at the Threshold of the 21st Century: Looking Ahead", 5th Conference of the International Soil Tillage Research Organisation (ISTRO). Fort Worth, Texas, USA, 2-7 July 2000

Soil degradation is a major problem in west African land use environments. Although burning of crop residue is known to enhance soil degradation, it is still the most commonly used practice for land preparation. Intercropping with herbaceous legumes is a promising method to combat fertility decline and minimise resource degradation. A study was conducted from 1996 to 1999 in southwestern Nigeria to investigate the interaction of residue burning and legume intercropping on soil degradation as an improved and practical approach toward rehabilitating and conserving an Alfisol. Leguminous cover crops, [Mucuna pruriens (mucuna), and Pueraria phaseoloides (pueraria) with grain legumes [Vigna unguiculata (cowpea)] as control were intercropped with maize in 1996 and 1998; yam was cultivated in 1997 and 1999. Following local practices, mound tillage with hoe was adopted since 1997 for yam production. Subtreatments were burning and mulching of residues from the cover crops, cowpea and maize. Soil erosion and yam mound stability were used as sustainability indicators. The weighted annual mean erosivity was 6.5 103 MJ mm ha-1h-1 (EI30 index), 422 cm2 h-1 for the AIm index. Mean runoff amounts ranged from 20 to 32 mm in 1996, from 94 to 158 mm in 1997, and from 37 to 103 mm in 1998. Mean soil erosion ranged from 0.9 to 2.1 Mg ha-1 in 1996, from 3.8 to 7.8 Mg ha-1 in 1997, and from 1.8 to 3.7 Mg ha-1 in 1998. The burned residue plots had higher runoff and soil erosion than the unburned residue plots. Soil particles were eroded in proportions similar to plot particle size distribution. Mounding in 1997 accentuated soil erosion although transportation of detached soil by runoff was impeded by the mounds. Variations in mound heights were due to accretion as well as removal of soil from the furrows. There was no significant difference in soil erosion between the cover crops and cowpea. Yam mound erodibility (slumping) was largely determined by the length of exposure to rain in the 1998 cropping season. Mounds on the burned residue plot of each legume, except cowpea, slumped more than mounds on the unburned residue plot between April and August 1998 . The combined yields (1996-98) of maize, grain and yam tuber were higher in the unburned residue treatment compared to the burned residue treatment. Cover crop intercropping resulted in higher crop yield than the cowpea. We concluded that the Alfisol is best managed for sustainable crop production by no tillage, residue mulching and cover cropping. Residue burning should be avoided even if cover crops are used.

Schafer B.M. and Kirchhof G. (2000). Soil and Climate for Lowland Rice-based Cropping systems in the Philippines and Indonesia. Soil and Tillage research. 56, 15-35.

Soil morphological, physical, chemical and mineralogical properties are described at five locations in major rice (Oryza sativa L.) growing areas of the Philippines (two sites) and in Indonesia (three sites) which were selected for lowland rice-based cropping systems research. The data were used to classify the soils into the local soil series, soil taxonomy and The Australian Soil Classification systems. These data were intended to facilitate transfer of knowledge of improved farming systems technology to other lowland rice growing areas in the regions. The soils were classified as Andsisols, Inceptisols and Vertisols, and were characterised by clay contents ranging from 370 to 870 g kg-1 and cation exchange values ranging between 17 and 68 cmol (p+) kg-1 for whole soil. pH values were neutral to mildly alkaline. Land surface and root zone attributes were qualitatively evaluated for limitations to post-rice crop production by interpretation of modified surface and sub-soil properties associated with rice production. Leakiness of bunds was also examined and mainly attributed to biological activity and for the development of drainage channels. Climatic data are presented for each of the five sites and the characteristics for potential rainfall incidence are given for the post-rice dry season crop period. The soil sites selected have a range of properties which are deemed to represent large areas of soils used for rice production in these two countries.

So H.B, and Kirchhof G., (2000). Guest Editors, Special Issue: Management of clay soils for rainfed lowland rice-based cropping systems. Soil and Tillage research. 56, 188pp.

The theme of this special issue is expressed by the title of this editorial. The papers in this special issue are derived from an international conference with the same title, held in November 1995 at the Bureau of Soil and Water Management (BSWM) in Manila. The conference was sponsored and funded by the Australian Center for International Agricultural Research (ACIAR) to review and summarise the results of an international collaborative project (Project 8938) involving Indonesia, the Philippines and Australia. Also invited were scientists from a range of other countries and institutions with expertise on rice-based systems. These include scientists from the International Rice Research Institute (IRRI), the Philippine Rice Research Institute, Tamil Naidu University in southern India, and the Rice-Wheat Consortium in India, ICRISAT and the CSIRO Division of Water Resources in Griffith, Australia. The conference covered both irrigated and rainfed lowland rice-based cropping systems. Papers from the conference can be found in the edited conference proceedings published by ACIAR (Kirchhof and So, 1996). This special issue contains selected and revised papers from these proceedings, based on the outcome of the conference. Rice is the most important staple food in Asian countries. The 1994 UN Food and Agriculture Organisation (FAO) Yearbook stated that the total global area under rice was 147 million ha, and 130 million of that is in Asia. Records from the International Rice Research Institute (IRRI) in 1995 showed that the vast majority of rice is grown as paddy or lowland rice, either under irrigated (81 million ha globally, 93% in Asia) or dryland conditions (40 million ha). The most common and traditional soil management strategy for paddy rice is to puddle (wet cultivation) the soil before. rice seedlings are manually transplanted. Puddling is in fact the most important soil management practice for rice production. It serves primarily to reduce the soil's hydraulic conductivity and to ensure that inundated conditions are maintained during the cropping cycle so that weeds are easily controlled and water stress avoided. It creates a soft soil and makes transplanting of seedlings easy and allows rapid establishment of the transplanted seedlings. This system has been practised for centuries and was derived from the time when rice was a long season crop of 150 days or longer. At that time, it was essential that seeds be germinated very early to take advantage of the first rain of the season and gain time while preparing the land. It was later transplanted which allows the inundated rice crop to ®t within the rainy season. Thus, early germination is then essential to avoid terminal water stress and avoid the risk of reduced yields. However, with the modern, short season, high yielding rice cultivars, the need for early germination is no longer essential for the success of the crop. However, as old habits are not easily altered, the practice has not changed substantially despite significant efforts being invested into dry seeding of rice. Where irrigation is available, inundated conditions can be maintained to grow two or three lowland rice crops a year. Where irrigation is not available, one lowland rice crop is generally grown under rain-fed conditions during the rainy season, and only during periods where rainfall exceeds 200 mm a month. Where rainfall is erratic, the rice crop may be grown as lowland but may complete its cycle as an upland crop. It is generally accepted that inundated conditions can be maintained if rainfall exceeds the amount of water lost through evaporation (an average of 4 mm/day) and percolation which must be kept to 2 mm/day or less. Hence a primary reason for puddling is to reduce the soils' hydraulic conductivity. However, the previously puddled soil layer poses considerable restrictions on cropping after rice. Although beneficial for rice, soil puddling has an adverse effect on the physical properties of the soil. Anaerobic conditions are unfavourable for upland crop establishment and growth while the puddled layer is wet. Upon drying it becomes dry very quickly and will severely restrict root growth. Following several months of inundation during the rice phase, the subsoil water contents are generally high and except in sandy soils, it is generally sufficient to grow an upland crop with a moderate to high yield, such as legumes, provided the crop can access that water. However, yields of these dry season crops under rainfed conditions are generally very low and unreliable. Yields of mungbean of

So H.B, and Kirchhof G., (2000). Management of clay soils for rainfed lowland rice-based cropping systems. Soil and Tillage research. 56, 1-2.

The theme of this special issue is expressed by the title of this editorial. The papers in this special issue are derived from an international conference with the same title, held in November 1995 at the Bureau of Soil and Water Management (BSWM) in Manila. The conference was sponsored and funded by the Australian Center for International Agricultural Research (ACIAR) to review and summarise the results of an international collaborative project (Project 8938) involving Indonesia, the Philippines and Australia. Also invited were scientists from a range of other countries and institutions with expertise on rice-based systems. These include scientists from the International Rice Research Institute (IRRI), the Philippine Rice Research Institute, Tamil Naidu University in southern India, and the Rice-Wheat Consortium in India, ICRISAT and the CSIRO Division of Water Resources in Griffth, Australia. The conference covered both irrigated and rainfed lowland rice-based cropping systems. Papers from the conference can be found in the edited conference proceedings published by ACIAR (Kirchhof and So, 1996). This special issue contains selected and revised papers from these proceedings, based on the outcome of the conference. Rice is the most important staple food in Asian countries. The 1994 UN Food and Agriculture Organisation (FAO) Yearbook stated that the total global area under rice was 147 million ha, and 130 million of that is in Asia. Records from the International Rice Research Institute (IRRI) in 1995 showed that the vast majority of rice is grown as paddy or lowland rice, either under irrigated (81 million ha globally, 93% in Asia) or dryland conditions (40 million ha). The most common and traditional soil management strategy for paddy rice is to puddle (wet cultivation) the soil before rice seedlings are manually transplanted. Puddling is in fact the most important soil management practice for rice production. It serves primarily to reduce the soil's hydraulic conductivity and to ensure that inundated conditions are maintained during the cropping cycle so that weeds are easily controlled and water stress avoided. It creates a soft soil and makes transplanting of seedlings easy and allows rapid establishment of the transplanted seedlings. This system has been practised for centuries and was derived from the time when rice was a long season crop of 150 days or longer. At that time, it was essential that seeds be germinated very early to take advantage of the first rain of the season and gain time while preparing the land. It was later transplanted which allows the inundated rice crop to fit within the rainy season. Thus, early germination is then essential to avoid terminal water stress and avoid the risk of reduced yields. However, with the modern, short season, high yielding rice cultivars, the need for early germination is no longer essential for the success of the crop. However, as old habits are not easily altered, the practice has not changed substantially despite significant efforts being invested into dry seeding of rice. Where irrigation is available, inundated conditions can be maintained to grow two or three lowland rice crops a year. Where irrigation is not available, one lowland rice crop is generally grown under rainfed conditions during the rainy season, and only during periods where rainfall exceeds 200 mm a month. Where rainfall is erratic, the rice crop may be grown as lowland but may complete its cycle as an upland crop. It is generally accepted that inundated conditions can be maintained if rainfall exceeds the amount of water lost through evaporation (an average of 4 mm/ day) and percolation which must be kept to 2 mm/day or less. Hence a primary reason for puddling is to reduce the soils' hydraulic conductivity. However, the previously puddled soil layer poses considerable restrictions on cropping after rice. Although beneficial for rice, soil puddling has an adverse effect on the physical properties of the soil. Anaerobic conditions are unfavourable for upland crop establishment and growth while the puddled layer is wet. Upon drying it becomes dry very quickly and will severely restrict root growth. Following several months of inundation during the rice phase, the subsoil water contents are generally high and except in sandy soils, it is generally sufficient to grow an upland crop with a moderate to high yield, such as legumes, provided the crop can access that water. However, yields of these dry season crops under rainfed conditions are generally very low and unreliable. Yields of mungbean of

So, H.B., Kirchhof, G., Bakker, R., Smith, G.D. (2000). Low Input Tillage/Cropping Systems for Limited Resource Areas. Proceedings, "Tillage at the Threshold of the 21st Century: Looking Ahead", 5th Conference of the International Soil Tillage Research Organisation (ISTRO). Fort Worth, Texas, USA, 2-7 July 2000.

Agricultue in limited resource areas is characterized by small farms which are generally too small to adequately support the needs of an average farm family. The farming operation can be described as a low input cropping system with the main energy source being manual labor, draught animals and in some areas hand tractors. These farming systems are the most important contributor to the national economy of many developing countries. The role of tillage is similar in dryland agricultural systems in both the high input (HICS) and low input cropping systems (LICS), however, wet cultivation or puddling is unique to lowland rice-based systems in low input cropping systems. Evidence suggest that tillage may result in marginal increases in crop yield in the short term, however, in the longer term it may be neutral or give rise to yield decreases associated with soil structural degradation. On marginal soils, tillage may be required to prepare suitable seedbeds or to release adequate Nitrogen through mineralization, but in the longer term, however, tillage reduces soil organic matter content, increases soil erodibility and the emission of greenhouse gases. Tillage in low input cropping systems involves a very large proportion of the population and any changes in current practices such as increased mechanization will have a large social impact such as increased unemployment and increasing feminization of poverty, as mechanization may actually reduce jobs for women. Rapid mechanization is likely to result in failures, but slower change, accompanied by measures to provide alternative rural employment, might be benefcial. Agriculture in limited resource areas must produce the food and fibre needs of their community, and its future depends on the development of sustainable tillage/cropping systems that are suitable for the soil and climatic conditions. These should be based on sound biophysical principles and meet the needs of and be acceptable to the farming communities. Some of the principle requirements for a sustainable system includes the maintenance of soil health, an increase in the rain water use efficiency of the system, increased use of fertilizer and the prevention of erosion. The maintenance of crop residues on the surface is paramount for meeting these requirements, and the competing use of crop residues must be met from other sources. These requirements can be met within a zonal tillage system combined with suitable agroforestry, which will reduce the need for crop residues. It is, however, essential that farmers participate in the development of any new technologies to ensure adoption of the new system.

Tian, G., G. O. Kolawole, B. T. Kang and G. Kirchhof (2000). Nitrogen fertilizer replacement indexes of legume cover crops in the derived savanna of West Africa. Plant and Soil 224(2): 287-296.

Legume cover crops are a potential means for overcoming N depletion in the derived savanna of West Africa. A 3-year trial was, therefore, conducted near Ibadan, southwestern Nigeria to measure the N contribution of 13 legume cover crops as compared to urea -N, using a N fertilizer replacement index for a maize test crop. Two series of trials involved the following legume cover crop species: Aeschynomene histrix, Centrosema brasilianum, Centrosema pascuorum, Chamaecrista rotundifolia, Cajanus cajan, Crotalaria verrucosa, Crotalaria ochroleuca, Lablab purpureus, Mucuna pruriens, Psophocarpus palustris, Pseudovigna argentea, Pueraria phaseoloides and Stylosanthes hamata. Trials were undertaken using a complete block design. Cover crops were planted in 1994 (Series 1) and 1995 (Series 2) in separate sites and each series was subsequently slashed and planted for one season with maize (Zea mays) in 1995 and 1996. At the 50% flowering stage, N concentration of above-ground vegetation of cover crops ranged from 21 to 38 g N kg(-1). Nitrogen accumulated by 4.5-month old cover crops ranged from 14 to 240 kg N ha(-1), depending on species and year. Cover crops increased grain yield of the subsequent maize crop by 25-136% over the control without N application. Nitrogen uptake by the maize crop was higher following cover crops than after maize or natural grass. The N fertilizer replacement index of cover crops for maize ranged from 11 (A. histrix) to 96 kg N ha(-1) (C. cajan) in Series 2. Perennial ( C. brasilianum, S. hamata, C. cajan, P. phaseoloides and C. verrucosa) and annual (C. rotundifolia, M. pruriens, C. ochroleuca and L. purpureus) species could potentially save 50 to 100 kg N ha(-1) for maize crops. The cover crops accumulated more N in the wetter than in the drier year. However, the N fertilizer replacement index was higher for subsequent maize grown in the drier year. The cover crop-N recovery in maize was also higher than the urea-N uptake in the drier year. The N fertilizer replacement indexes can be predicted using the above-ground biomass amount of cover crops at 20 weeks after planting (drier year) or the N concentration at that stage (wetter year).

Tian, G., Kolawole G.O., Kang, B.T., Kirchhof, G. (2000). Nitrogen fertiliser replacement indexes of legume cover crops in the derived savanna of West Africa. Plant and Soil. 224(2): 287-296.

Legume cover crops are a potential means for overcoming N depletion in the derived savanna of West Africa. A 3-year trial was, therefore, conducted near Ibadan, southwestern Nigeria to measure the N contribution of 13 legume cover crops as compared to urea –N, using a N fertilizer replacement index for a maize test crop. Two series of trials involved the following legume cover crop species: Aeschynomene histrix, Centrosema brasilianum, Centrosema pascuorum, Chamaecrista rotundifolia, Cajanus cajan, Crotalaria verrucosa, Crotalaria ochroleuca, Lablab purpureus, Mucuna pruriens, Psophocarpus palustris, Pseudovigna argentea, Pueraria phaseoloides and Stylosanthes hamata. Trials were undertaken using a complete block design. Cover crops were planted in 1994 (Series 1) and 1995 (Series 2) in separate sites and each series was subsequently slashed and planted for one season with maize (Zea mays) in 1995 and 1996. At the 50% flowering stage, N concentration of above-ground vegetation of cover crops ranged from 21 to 38 g N kg??1. Nitrogen accumulated by 4.5-month old cover crops ranged from 14 to 240 kg N ha??1, depending on species and year. Cover crops increased grain yield of the subsequent maize crop by 25–136% over the control without N application. Nitrogen uptake by the maize crop was higher following cover crops than after maize or natural grass. The N fertilizer replacement index of cover crops for maize ranged from 11 (A. histrix) to 96 kg N ha??1 (C. cajan) in Series 2. Perennial (C. brasilianum, S. hamata, C. cajan, P. phaseoloides and C. verrucosa) and annual (C. rotundifolia, M. pruriens, C. ochroleuca and L. purpureus) species could potentially save 50 to 100 kg N ha??1 for maize crops. The cover crops accumulated more N in the wetter than in the drier year. However, the N fertilizer replacement index was higher for subsequent maize grown in the drier year. The cover crop-N recovery in maize was also higher than the urea-N uptake in the drier year. The N fertilizer replacement indexes can be predicted using the above-ground biomass amount of cover crops at 20 weeks after planting (drier year) or the N concentration at that stage (wetter year).

Bakti L.A.A., So H.B. and Kirchhof G. (1998). Changes in some physical properties of puddled soil during drying. ASSSI National Soils Conference, Brisbane, 27-29 April 1998, Conference Proceedings, 409-412.

Kirchhof G. and Salako F.K. (1998). Residual Tillage Effects and soil erosion after bush fallow on a tropical Alfisol in a legume based intercropping system. ASSSI National Soils Conference, Brisbane, 27-29 April 1998, Conference Proceedings, 47-55.

The effects of pre-fallow tillage practices on the productivity of a 6 year fallowed tropical Alfisol was investigated in South Western Nigeria. Post-fallow land use in 1996 was maize production intercropped with legume. The parameters evaluated included soil properties, ground cover, crop growth and yield, rainfall erosivity, runoff and soil loss. In spite of the six-year bush fallow and establishment of cover crops, soil erosion was significantly higher on plots previously under conventional tillage compared to no - tillage plots. Crop growth and yields were low on the previous bare plot which had maximum erosion compared to the previously cropped plots in spite of bush fallowing. Maize grain yield was highest under Pueraria phaseoloides intercrop (2.15 t/ha) followed by Cowpea intercrop (1.92 t/ha), sole maize (1.87 t/ha) and Mucuna pruriens intercrop (1.7 t/ha). Soil erosion was moderate under this system. However, Pueraria performed best as an intercrop for soil conservation in this first year of intercropping.

Rahmianna A.A., So H.B. and Kirchhof G. (1998). Comparison of performance of mungbean germination obtained form the laboratory, glasshouse and field trials. ASSSI National Soils Conference, Brisbane, 27-29 April 1998, Conference Proceedings, 416-417.

Adisarwanto T., Utomo W.H., Kirchhof G., So H.B. (1996). Response of food legume crops to different soil management practises after rainfed lowland rice in east Java. IN: Management of Clay soils for Rainfed Lowland Rice Based Cropping Systems, ACIAR Proceedings No. 70, 1996, 142-147. Eds: Kirchhof G. and So H.B.

Bakti L.A.A., So H.B. and Kirchhof G. (1996). Effect of puddling on soil physical properties during rice growth. Abstracts, Joint Australian and New Zealand Soil Science Conference, University of Melbourne, 7-11 July 1996. Volume 3, Poster Papers, 13-14.

Daquiado N.P., So H.B. and Kirchhof G. (1996). Hardsetting behaviour of some Australian and Philippines Soils. Abstracts, Joint Australian and New Zealand Soil Science Conference, University of Melbourne, 7-11 July 1996. . Volume 3, Poster Papers, 57-58.

Kirchhof G. (1996). Image analysis applications in soil and crop science. ACTA Phytoecologica Sinica.

Kirchhof G. , So H.B. (1996). The effect of puddling intensity and compaction on properties, rice and mungbean growth: A mini rice-bed study. IN: Management of Clay soils for Lowland Rice Based Cropping Systems, ACIAR Proceedings No 70, 1996, 51-70. Eds: Kirchhof G. and So H.B.

Kirchhof G., So H.B., Adisarwanto T., Utomo W.H., Priyono S., Elicano D.T., Castaneda V.E. Urriza G.I.P., Alcasid G.N. jr (1996). Post rice climatic variability and legume yields. IN: Management of Clay soils for Rainfed Lowland Rice Based Cropping Systems, ACIAR Proceedings No. 70, 1996, 159-170. Eds: Kirchhof G. and So H.B.

Management of Clay soils for Rainfed Lowland Rice-Based Cropping Systems, ACIAR Proceedings No. 70, 1996. ISBN 1 86320 176 9, Eds: Kirchhof G. and So H.B., 259 p.

In Asian countries rice is the most important staple food. The most common practice for paddy rice is to puddle the soil before rice seedlings are planted. Puddling is the most important soil management strategy for rice production. Where irrigation is not available, rice is generally grown under rainfed conditions during the rainy season. It is possible for upland crops to be planted after lowland rice in rainfed areas. However, the yields are very low, and the previously puddled soil layer poses considerable restrictions on cropping after rice. Therefore, development of suitable management practices to grow food legumes after the rice crop on these puddled soils would be particularly advantageous. These proceedings are the result of a workshop held in Quezon City, Philippines in November 1995, and present the results of this research as well as papers presented on related research from the international scientific community.

Priyono S., Kirchhof G., So H.B., Utomo W.H. (1996). Effect of puddling on root growth and subsoil water use of rainfed legumes after rice. IN: Management of Clay soils for Lowland Rice Based Cropping Systems, ACIAR Proceedings No. 70, 1996, 99-108. Eds: Kirchhof G. and So H.B.

Rahmianna A.A., So H.B., Kirchhof G., Sumarno, Adisarwanto T. (1996). Crop establishment of Legumes in lowland rice based cropping systems. IN: Management of Clay soils for Rainfed Lowland Rice Based Cropping Systems, ACIAR Proceedings No 70, 1996, 109-115. Eds: Kirchhof G. and So H.B.

Rahmianna A.A., So H.B., Kirchhof G., Sumarno, Adisarwanto T. (1996). Crop establishment of legumes in lowland rice-based cropping systems. Abstracts, Joint Australian and New Zealand Soil Science Conference, University of Melbourne, 7-11 July 1996. . Volume 3, Poster Papers, 213-214.

Schafer B.M., Kirchhof G. (1996). Soil and Climate Description of Benchmark Sites for Lowland Rice-based Cropping systems Research in the Philippines and Indonesia. IN: Management of Clay soils for Lowland Rice Based Cropping Systems, ACIAR Proceedings 70, 1996, 29-50. Eds: Kirchhof G. and So H.B.

So H.B., Kirchhof G., Utomo W.H, Adisarwanto T., Prastowo B., Dacanay E.V., Alcasid G.N. jr. And Ringrose-Voase A.J. (1996). Management of Clay soils for lowland rice-based cropping systems: The Experiments and Methodology. IN: Management of Clay soils in Lowland Rice Based Cropping Systems, ACIAR Proceedings No. 70, 1996, 25-28. Eds: Kirchhof G. and So H.B.

So. H.B., Kirchhof G., Ringrose-Voase A. (1996). Management of clay soils for rainfed lowland rice-based cropping systems. Abstracts, Joint Australian and New Zealand Soil Science Conference, University of Melbourne, 7-11 July 1996. . Volume 3, Poster Papers, 235-236.

Utomo W.H., Prastowo B., Adisarwanto T., Dacanay E.V, Kirchhof G., So H.B.(1996). Soil Puddling and Rice growth. . IN: Management of Clay soils in Lowland Rice Based Cropping Systems, ACIAR Proceedings No. 70, 1996, 90-94. Eds: Kirchhof G. and So H.B.

Jayawardane N.S., Barrs H.D., Muirhead W.A., Blackwell J., Murray E. and Kirchhof G. (1995). Lime slotting technique to ameliorate sub-soil acidity in a clay soil. II Effects on medic root growth, water extraction and yield. Australian Journal of Soil Research. 33, 443-459.

Subsoil acidity causes low crop production, which is often associated with shallow root development and restricted soil water extraction. In part I of this series, lime-slotting of an acid soil was shown to improve the soil physical and chemical characteristics for root growth. In a lysimeter study on an acid soil, the effects of several soil ameliorative treatments on root growth, water extraction and yields of a medic crop were evaluated. Large lysimeter cores of 0.75 m diameter and 1.35 m deep were used. The soil treatments included a non-ameliorated acid soil, lime-slotting with a 0.15 m wide and 0.8 m deep slot containing 20 t ha-1 of lime, lime-slotting combined with surface phospho-gypsum application at 10 t ha-1, and complete amelioration of the entire soil volume by mixing lime at 133 t ha-1 and repacking to a low bulk density of 1.1 t m-3. In the non-ameliorated acid soil, medic roots were confined to the surface (0.1 m) layer, resulting in limited water extraction of 32 mm during a prolonged drying cycle, and a low dry matter yield of 70 g m-2. In the lime slotted soil, roots grew within the slot to its full depth, although penetration into the undisturbed soil was restricted to the soil immediately adjacent to the slot. Consequently, the root length per unit surface area (La) at depths below 0.1 m depth was increased to 9.9 km m-2. During a drying cycle, water extraction increased to 58 mm. The increased water extraction came from both the slotted soil and the undisturbed soil between slots. This led to an increase in dry matter yields to 270 g m2. In lime-slotted soils with surface gypsum applications, the root growth and crop water extraction patterns were similar to the lime-slotted soil. Repacking limed soil resulted in similar root lengths (L(a) 10.0 km m-2) as lime-slotted soil. However, owing to more uniform distribution of roots in the repacked soil, water extraction was increased to 100 mm and yields increased to 590 g m-2. Yields of non-ameliorated soil were only 12% of the repacked, limed soil. However, lime-slotting which involves loosening only 25% of the soil surface area and addition of only one-sixth of the amount of lime required for complete soil amelioration, led to marked increases in yield (46% of the yield of repacked soil). Future field studies are required to evaluate the optimum limed-slot configurations required for different soils, crops and climatic regimes.

Jayawardane N.S., Blackwell J., Kirchhof G. and Muirhead W.A. (1995). Slotting - A deep tillage technique for ameliorating sodic, acid and other degraded subsoils and for land treatment of waste. Advances in Soil Science. (Lewis publishers). p 109-146.

Kirchhof G. and So H.B. (1995). Compaction on Vertisols: Can it be predicted? National Controlled Traffic Conference. Rockhampton, 13-14 September 1995, Proceedings. 196- 201.

Kirchhof G. and So H.B. (1995). Legumes after rainfed lowland rice. ACIAR Food Legume Newsletter No 22, April 1995, p 2-5.

Kirchhof G., Blackwell J., Hughes M., Parsons D.H. and Jayawardane N.S. (1995). Increasing cane yield by reducing both waterlogging and water stress. Final report to the Sugar Research and Development Cooperation. ISBN No 0 643 05780 3, 59p.

Kirchhof G., Jayawardane N.S., Blackwell J. and Murray E. (1995). Lime slotting technique to ameliorate sub-soil acidity in a clay soil. I Effects on soil pH and physical characteristics. Australian Journal of Soil Research. 33, 425-441

In soils with subsoil acidity, root growth of plants sensitive to acidity is restricted to surface layers resulting in reduced water and nutrient uptake and low yields of crops. In the present study, the use of the lime-slotting technique, with slots 0.15 m wide and 0.8 m deep, for providing long-term improvements of the adverse soil chemical and physical characteristics of an acid, clay soil was investigated. Lime-slotting using a rotary slotter resulted in a uniform increase in soil pH to the full depth of the slot (0.8 m), indicating a thorough mixing of the lime with the small soil fragments produced by slotting, as they are thrown up into the rotor shroud and redeposited in the slot. In contrast, ripping to 1.0 m depth and delve ploughing to 0.8 m depth only changed the soil pH close to the soil surface. The saturated hydraulic conductivity, total porosity and air-filled porosity at a potential of - 10 kPa measured on soil cores was significantly (P

Adisarwanto T., Utomo W.H., Kirchhof G. and So H.B. (1994). The effect of soil management practises on soybean after lowland rice on Vertisol. Proceedings, World Soybean Research Conference V, 21-27 February 1994, Chiang Mei, Thailand, 6pp.

Kirchhof G. (1994). Compaction Properties of Vertisols and their potential effect on sunflower. PhD thesis, Univ. of Qld.

Large areas of arable land in the eastern inland regions of Australia are dominated by cracking clay soils (Vertisols). The occurrence of compaction on these soils and its effect on crops is not well understood. This work investigated the effect of compaction on the growth and development of sunflowers and the response of a range of cracking clay soils to compactive forces. Compaction on Vertisols was expressed as bulk density corrected to a reference water content assuming the soil undergoes normal shrinkage. This presents a useful technique to quantify compaction of Vertisols in the field. Field experiments were carried out on a Vertisol (black earth) at the University of Queensland, Gatton College at Lawes, to investigate the effect of compaction on the growth of sunflowers and its influence on soil water contents during two growing seasons in 1984/85 and 1985/86. Treatments included an uncompacted control, low compaction and severe compaction. The uncompacted treatment was achieved by deep ripping to 40 cm followed by fallowing for several months. Compaction was induced using a road roller with a contact pressure of 100kPa; 1 pass and 4 passes with the roller were used for low and severe compaction respectively. In both years the compaction treatments were applied before sowing. A third experiment was conducted in 1985/86 on the site compacted in the previous year without re-inducing the compaction treatments to investigate the residual effects of compaction after self-amelioration of the soils in the absence of machinery traffic. In both years severe compaction reduced the early growth of the crop and amount and depth of water depletion was decreased. However, as the season progressed differences between treatments decreased. Final seed yields were reduced by 15% in 1984/85 under high compaction. This was related to bulk density values exceeding 1.39Mgm-3(at 0.3 gg-1) below the cultivated layer at 20 to 25 cm depth. Compaction only affected plant growth when it was induced at the start of the cropping season. Wetting and drying cycles over the period of one year in the absence of machinery traffic did eliminate soil compaction in the field experiments of this study. The response of clay soils to compactive forces was evaluated in the laboratory for soils found in major cotton growing areas in Queensland. A total of 70 sites were sampled from a wide range of soil types with clay contents varying from 30 to 73%, organic C from 0.8 to 5.7% and dispersible clay contents from 2 to 22%. Atterberg limits, water content at permanent wilting point, exchangeable cations and clay content of the soils used were strongly related and could be predicted from each other. of the soils used were strongly related and could be predicted from each other. A uni-axial compression test, using pressures and loading times similar to those occurring during the passage of agricultural vehicles, was developed and used to determine the response of these soils to compaction at different soil water contents. It was expressed using the relationship of bulk density to the soil water content at which compaction was carried out (compaction curves). Bulk density values reached a maximum value at an optimum water content depending on the magnitude of the compactive pressure applied. It was increased as uni-axial pressures increased and clay content decreased. Organic carbon decreased bulk density but its effect was small. The bulk densities at maximum compaction as well as bulk densities at water contents lower than the optimum water content were related to applied pressure, texture and water content at which the soil was compacted and could be predicted with a high degree of reliability. The equation for bulk density at water contents less than the optimum is: Bd = 1.425 - 0.986 clay + 0.144 ln p + 0.530 Wg n = 507, r2 = 0.71 and where Bd = bulk density [Mgm-3] clay = clay content [gg-1] p = uni-axial pressure [kPa 10-2 (Bar)] Wg = gravimetric water content [gg-1] This equation should be able to be developed into useful field model and a management tool. ation should be able to be developed into useful field model and a management tool. The potential effects of compaction on soil productivity were associated with the change in the soil pore size distribution. Compaction reduced the volume of large pores and slightly increased the volume of small pores. This resulted in slightly lower amounts of plant available water but a strong decrease in saturated hydraulic conductivity in soils at high bulk density values. Compaction can be expected to become harmful to crop growth when a threshold bulk density was exceeded. The threshold bulk density for growth and yield of sunflower on vertisols (black earths) at the University of Queensland, Gatton College at Lawes was 1.39 Mgm-3 (corrected to a water content of 0.3 gg-1). This value was close to that of maximum compaction achievable corresponding to an air filled porosity of about 6% which is likely to be simular for other vertisols and crop types.

Kirchhof G. and So H.B. (1994). Soil puddling for rice production and its effect on soil structure and water percolation. Proceedings, International Symposium on Sealing, Crusting and Hardsetting Soils: Productivity and Conservation. Brisbane, Qld, Australia; The University of Queensland, 7-11 February 1994, 413-419.

Puddling intensity was quantified and expressed as the ratio of puddled soil volume versus total soil volume. This expression integrated the effects of speed, time and shape of the puddling implement and was well related to soil dispersion, bulk density and saturated hydraulic conductivity. Following prolonged periods of submerged conditions during rice growth, saturated hydraulic conductivity decreased despite a concomitant reduction in soil dispersion. There was indication that continuous water logging reduced the effect of soil puddling, in particular on heavy textured soils. Heavy textured soils also appeared to recover more readily from soil structural deterioration from soil puddling than lighter textures soils after one or more drying cycles.

Kirchhof G., Alcasid Jr. (1994). Management of clay soils for lowland rice based cropping systems. The Philippine Journal of Crop Science, Volume 19, Supplement 1, May 1994. p53.

Kirchhof G. and Pender C. (1993). SCI-SCAN image analysis system - Manual, Image Analysis made easy (187pp). Note: There are two version of the SCI-SCAN manual. This has now been replaced with the commercial version by Delta-T, edited by Dr Nick Webb.

So H.B. and Kirchhof G. (1993). Management of Clay Soils under Low-land Rice Based Cropping Systems. ACIAR Food Legume Newsletter No 18, April 1993, p 7-8.

So H.B. Kirchhof G. and Basnet B.B. (1993). Soil Physics Laboratory Manual, Department of Agriculture, The University of Queensland, St Lucia Qld. 4072, 98 pp

Blackwell J., Jayawardane N.S., Kirchhof G. and Smart R. (1992). Use of sludge-Slotting to dispose of and utilise Sewage and other waste on agricultural land. CSIRO Division of Water Resources, Divisional Report 92/4. Eds: K.H. Bowmer and P.Laut, Seeking Solutions, 19 - 21.

Kirchhof G. (1992). Measurement of root length and thickness using a hand held computer scanner. Field Crops Research. 29, 79-88.

A hand-held computer scanner was used to produce images of lines randomly drawn on a sheet of paper which could simulate roots. The binary images were analysed for total length using the intercept method and distribution of line thicknesses. The number of intercepts was normalized with respect to image size and resolution. This value, in conjunction with the fraction of line cover in the image, was used to obtain an equation to predict length (normalized with respect to picture size) from number of normalized intercept counts. The derived calibration equation (r2=0.008, cv=1.7%) predicted the length irrespective of thickness and distribution of thickness. The intercept method was extended to determine the length of lines with different thicknesses within the image. It was possible to resolve line thickness differences of 0.15 mm for thicknesses ranging from 0.15 to 0.7 mm. Although the total length, determined as the cumulative length of all thickness intervals, was lower than the real total length, the relative distribution of thicknesses was accurate to 2%. From length and thickness of lines in each interval, its surface area could be calculated, assuming a cylindrical shape. The major advantages of using a hand-held scanner for root length determinations are: (i) very low cost, compared to other image analysis systems; (ii), high resolution (>0.063 mm); (iii) actual size of the image is automatically recorded; (iv) small size of the scanner; and (v) image size is independent of the video screen size.

Kirchhof G., Pender C., Daniel H. (1992). The use of computer scanners for image analysis in soil science and Agronomy. Abstracts, National Soil Conference, Adelaide, Australia, 19-23 April 1992. p 152.

Jayawardane N.S., Blackwell J., Muirhead W.A., Kirchhof G. and Smart R.E. (1991). Gypsum and lime slotting - A new deep tillage technique for improved crop production on sodic and acidic soils. Soil Tillage and Agricultural Sustainability, Proceedings, 12th International Conference, ISTRO. Ibadan, Nigeria 8-12 July 1991.

Kirchhof G, Blackwell J., Rawlinson L. and Walsh J. (1991). Use of soil slotting to incorporate sludge as a soil ameliorant. AWWA/WPCF Joint Residuals Management Conference, 'Residuals Management after 1991'. Durham, NC, August 11-14, 1991.

Kirchhof G., Blackwell J. and Smart R.E. (1991) Growth of vineyard roots in segmentally ameliorated acid subsoils. Plant and Soil, 134, 121-126. ALSO IN: Plant Soil Interactions at low pH, Edt. by R.J.Wright et al., June 1991, 447-452.

Grapevine growth and production is limited in the Port Macquarie region by acidic subsoils and high exchangeable aluminium. Root growth is restricted to about 15 cm depth, and despite high growing season rainfall (920 mm, September to March) which exceeds predicted evapotranspiration for the period (400 mm), the vines suffer periodic water stress. Slotting is a technique of subsoil amelioration allowing thorough incorporation of lime to depth. Slots are 150 mm wide, and in this experiment were installed to 400 mm depth. The aim of slotting is to improve root growth in the subsoil, thus increasing plant access to water and nutrients previously inaccessible. The experiment was conducted in a Chardonnay vineyard planted in 1982. Lime was incorporated into the slots at about 2 t ha 1 with a further 8 t ha -1 spread on the surface, mixed and moved to form an under vine bank. Soil and root samples were taken in February, 1990. Slotting caused pH(CaCl2) to increase from 4.3 to 5.0 to 400 mm depth. Associated with this was a more than ten-fold increase in root length density. The slotting technique gives the opportunity to improve dense, poorly drained acidic soils and make them suitable for horticulture production.

Smart R.E., Kirchhof G. and Blackwell J. (1991). The diagnosis and treatment of acidic vineyard soil. Wine Industry Journal, Feb.1991, 35-40.

Blackwell J., Kirchhof G., Smart R.E. and Jayawardane N. (1990). (Article on soil slotting in vineyards) Good fruit and vegetables, Oct. Ed.

Kirby M. and Kirchhof G. (1990) The compaction process and factors affecting soil compactibility. Soil Compaction Workshop, Toowoomba, 15 - 17 Oct 1990, 28-31

Kirchhof G., Blackwell J. and Smart R.E. (1990) Growth of vineyard roots in segmentally ameliorated acid subsoils. 2nd international symposium on Plant-Soil Interactions on Acid Soils. West Virginia (Abstract p.97)

Kirchhof G., Jayawardane N.S., Blackwell J. and Muirhead W.A. (1990). Amelioration of acidic subsoils. Proceedings 5th Australian Soil Conservation Conference - Stable Cropping systems - Geralton, W.A., 49-55.

Kirchhof G. and So H.B. (1989). The compactibility of clay soils (Vertisols). Abstracts, Soil compaction as a factor determining plant productivity, International Conference, 5 - 9 June 1989, Lublin Poland, 91-92.

Kirchhof G. and So H.B. (1988). Susceptibility of clay soils to compaction. Abstracts, Australian National Soils Conference. Canberra. p.207.

Kirchhof G., Schafer B.M. and So H.B. (1988). Compactibility of soils used for cotton production. 4th Australian Cotton Conference, Surfers Paradise, August 17th & 18th.

Kirchhof G. and So H.B. (1987). A Uni Axial compression test to determine compaction properties of soils. National Soil Physics Workshop. Toowoomba. 151-153a.

Kirchhof G., Schafer B.M. and So H.B. (1986). The effect of compaction on the growth and yield of sunflowers. Proc. 6th Austr. Sunflower Conference, Gunnedah. 62-66.

Kirchhof G.(1984). Soil physical changes in a duplex profile during a drying cycle. Dipl.Ing.agr. Thesis. Univ. of Hannover (FRG).

Muirhead W.A., Kirchhof G. and White R.J.G. (1984). Soil physical changes in a duplex profile during a drying cycle. CSIRO Div.of Irrigation Research, Griffith NSW, Annual Report 1983/84, 55-56.

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