The inclusion of shrub or tree legumes has underpinned animal feed systems in tropical regions especially in areas where the soil is of low fertility. In this respect, the inclusion of Stylosanthes spp. is considered to be an ideal low cost method of improving the quality and dietary value of pastures in northern Australia, Northeast Thailand and southern China. The introduction of legumes has had a significant positive impact on the profitability of the large and small ruminant, pig and poultry industries and the well being of the local population in each of these countries. However, increasing use of legumes and accompanying management practices is not without the land degradation problems of accelerated soil acidification and nutrient depletion that brings into question the sustainability of these systems. The purpose of this project is to reverse the negative impacts of accelerated acidification and nutrient depletion through the development of innovative methods of preventing or limiting these processes.

The project involves collaboration between CSIRO (Land and Water, Townsville), Queensland Department of Natural Resources and Mines (DNRM, Brisbane and Mareeba), Chinese Academy of Tropical Agricultural Science (CATAS, Danzhou, Hainan) and Khon Kaen University, Khon Kaen Thailand. The project was formally initiated in October 2000 with the signing of an MOU between the Australian and Thai governments.

Key research progress and findings during the past 9 months include:
The collection of soil samples from paired sites identified in Hainan and Northeast Thailand and initiation of chemical and physical analysis.
Confirmation that on two sites in Northeast Thailand significant acidification has occurred to depth associated with changed land use.
Quantification of differences in root distribution patterns of selected grass species grown on light textured compacted sands in Northeast Thailand.
Installation of soil moisture monitoring, temperature probes, and automated rain gauge at a field site in Northeast Thailand. Associated with this activity has been the development of a web-based data handling system that down loads the data logger at this site via a digital mobile phone from Townville on a daily basis.
Installation of mini lysimeters at a site near Mareeba, north Queensland and the estimation of net acidification associated with nitrate leaching and product export from a Digitaria pasture and pinto peanut crop.
Establishment of field trials in Hainan and Northeast Thailand assessing different strategies for remediating degraded acid soils.
The establishment of a field trial in Hainan to assess selected strategies for remediating Stylosanthes dominance in pasture systems and wood weed encroachment.
Greenhouse studies have shown that the application of soil amendments can significantly increase the nutrient holding capacity of degraded soils. Associated with this increase nutrient holding capacity was a significant increase in the productivity of forage sorghum.
An assessment of pH buffer capacity pedotransfer functions (National Land and Water Audit sub-project) has indicated possible functions to be used in the development of an acidity risk assessment model.

In addition to the research component of the project, significant project resources were invested in the training of staff from partner countries and the communication of results. Training activities ranged from hands-on demonstrations and training in the running of remote automated soil and weather stations to the training of staff from Thailand and Hainan in soil chemical analysis and surface charge fingerprinting. Communication activities have included the publication of manuscripts in scientific journals and the presentation of results at an international conference on land degradation. Links have been maintained with other institutions in the region through regular exchange of information and the initiation of collaborative field trial sites.

Whilst this project is in its infancy, successful completion of this research will provide a number of potential economic, environmental and social benefits to communities and Governments including:
Base line data on land degradation associated with acidification under different crop/legume-based production systems in Southeast Asia.
The ability to target soil types that are prone to accelerated acidification and nutrient depletion and thereby provide knowledge at the farm planning level to minimize this negative impacts of current practices.
Identification of management practices in different crop/legume-based production systems in Southeast Asia that have the greatest impact on land degradation.
The development and establishment of a suite of practical options that can be used by producers to minimize soil acidification and nutrient loss.

The inclusion of shrub or tree legumes has underpinned animal feed systems in tropical regions especially in areas where the soil is of low fertility. In this respect, the inclusion of Stylosanthes spp. is considered to be an ideal low cost method of improving the quality and dietary value of pastures in northern Australia, Northeast Thailand and southern China. The introduction of legumes has had a significant positive impact on the profitability of the large and small ruminant, pig and poultry industries and the well being of the local population in each of these countries. However, increasing use of legumes and accompanying management practices is not without the land degradation problems of accelerated soil acidification and nutrient depletion that brings into question the sustainability of these systems. The purpose of this project is to reverse the negative impacts of accelerated acidification and nutrient depletion through the development of innovative methods of preventing or limiting these processes.
The project involves collaboration between CSIRO (Land and Water, Townsville), Queensland Department of Natural Resources and Mines (DNRM, Brisbane and Mareeba), Chinese Academy of Tropical Agricultural Science (CATAS, Danzhou, Hainan) and Khon Kaen University, Khon Kaen Thailand.
During the second year of the project the following were achieved. Surface charge fingerprinting of the paired sites in Thailand and China revealed that significant charge diminution and nutrients had occurred due to changed land use. The degree of chemical degradation was generally higher in Thailand than in China. It would appear the key driver in the decline in surface charge characteristics has been a reduction in soil organic matter and that surface soil horizons (0 - 10 cm) are most affected by changed management. These result highlights, in the case of Thailand, the fragility of these systems and their ability to adequate provide nutrients to growing crops. These sites form important 'benchmark' data sets that can be used in the future to reassess improvements to or deterioration in the chemical characteristics of these systems. Annual acid addition rates were estimated for Thailand and these ranged from 0.68 - 2.36 kmol H+/ha.yr., values that have commonly been measured in agricultural production systems in Australia.
Associated with the assessment of chemical degradation due to changed land use, pedotransfer functions to predict soil pH buffer capacity (pHBC) based on easily measured soil attributes (soil organic carbon and clay content) were developed for each country. pHBC is the intrinsic property of a soil that determines its innate ability to resist changes in soil pH due to acid or base additions. These pedotransfer functions will enable the development of soil acidity risk maps for each of the participating countries. In addition, a simple method for directly estimating this parameter was developed. This includes a simple Excel spreadsheet program that estimates the years that it would take for the soil pH to decline to a predetermined critical value (see enclosed computer program).
Continued monitoring of the root distribution patterns of selected grass species in Northeast Thailand has revealed that there is very little root growth below approximately 25 cm. However, monitoring of soil moisture contents at 50 and 100 cm respectively using Time Domain Reflectometry, has shown that during a drying phase soil moisture is extracted form these depths. These preliminary results suggest that relatively few roots are required at depth to significant influence the soil moisture patterns and possibly nutrient uptake. In a study undertaken at Mareeba, far North Queenslands, investigating the potential role of a deep rooted grass species in altering the bulk soil pH of a soil profile has shown after 12 months, that significant increases in soil pH to 60 cm under a nitrate fertilizer regime. Contrasting this, significant acidification was observed in those treatments receiving Urea as their sole nitrogen source. These results are extremely encouraging since they clearly demonstrate the ability of a deep root crop species, under a nitrate nitrogen fertilizer regime, to significantly alter the pH of the bulk soil. This potentially could be used as a management strategy to remediate subsoil acidity.
Preliminary studies evaluating the aluminium complexing ability of water soluble extracts from plant material has shown that by changing the form of nitrogen fertilizer, significant changes in the complexing ability can be achieved. Grass species that receive all of the nitrogen in a Urea form have a higher Al complexing ability than those receiving nitrogen in a nitrate form. Further studies are currently underway to evaluate different plant materials and understand the observed changes.
Over the past 12 months treatments evaluating the effect of various management strategies on reducing Stylosanthes dominance in pasture have been imposed on a trial site on the island of Hainan. Assessments of dry matter production and species composition have shown that at the end of the first growing season, fire has had a significant effect of reducing the legume component in the pasture and dry matter production. There is evidence to suggest that the over sown pasture (Brachairia) is starting to establish. Further monitoring of the site will continue over the next 12 months.
In addition to the research component of the project, significant project resources were invested into the training of post-graduate students in Thailand. A total of seven post-graduate students have projects that are associated with the project in Thailand. These students are under the supervision of Prof Sawaeng Ruaysoongnern. Communication activities have included the publication of manuscripts and the presentation of results at an international conference on land degradation. Links have been maintained with other institutions in the region through regular exchange of information and the initiation of collaborative field trial sites.
It is anticipated that successful completion of this research will provide a number of potential economic, environmental and social benefits to communities and Governments including:
Base line data on land degradation associated with acidification under different crop/legume-based production systems in Southeast Asia.
The ability to target soil types that are prone to accelerated acidification and nutrient depletion and thereby provide knowledge at the farm planning level to minimize this negative impacts of current practices.
Identification of management practices in different crop/legume-based production systems in Southeast Asia that have the greatest impact on land degradation.
The development and establishment of a suite of practical options that can be used by producers to minimize soil acidification and nutrient loss

Year 3 (01/07/2002-30/06/2003)
In Thailand, the 'paired sites' have been developed into a risk assessment map for predicting the potential rates of acidification under current land use systems. This has resulted in the development of a map that predicts the number of years until pH decreases to a level considered unproductive. Results of paired sites on soil degradation have been widely publicised and are in the process of integration into provincial development plans for soil and land resource rehabilitation. The concept of deep-rooted species on degraded soil rehabilitation is widely accepted by 16 farmer network all over the northeast of Thailand, and it is on the process of community research for agricultural resource development within the networks using the budget from Thailand Research Fund (TRF). Interactions between researchers and farmers in Participatory Research was revealed as an effective means of spreading, not only the results of this project, but techniques of research and the dissemination of other potential improvements to productivity and sustainability at the farm enterprise level. Thailand's Organic Farming Network is adopting clay technology for reduction of volatilized loss of ammonia from chicken manure compost both for during composting and post-application in organic farms. Farmers are appreciating the concept that alkalinity is exported in the crop, and its subsequent effect on soil acidification.
In China, the effects of management practices in reducing the dominance of legumes in pasture and thus reducing the potential for enhanced rates of acidification have been revealed, along with the potential to use the acidification buffering capacity of soils to develop a model for determining resources required to rejuvenate less productive lands. The design of field trials that will couple, for the first time, the benefits of using high-activity clay technologies with nitrate-based fertiliser schedules with deep rooted grass species to address the best combinations of technologies to alleviate and reverse soil acidification was shown.
A demonstration of the benefits of clays with high nutrient-holding capacity in enhancing productivity of grasses was undertaken in Thailand and Australia. The ability of nitrate-based nitrogen fertilisers to reverse acidification; in Australia to a depth of 90cm, was proven.

During the last 12 months there has been clear demonstration across three trial sites in Australia and Thailand that nitrate-nitrogen fertilised grass can increase soil pH down the profile. Aluminium (Al)-complexing abilities of a range of materials indicate that there is potential for using some of them as components of strategies for reducing acidification in relevant production systems. For example, King grass and eucalyptus residues have moderate Al-complexing abilities and might be useful as surface mulches on acidic soils in Hainan. Amendment trials in Thailand and Australia have shown that significant increases in yield are achieved following large applications of high-activity clays.
Results from bentonite trials in Australia demonstrated the benefit of concentrating the amount of bentonite added by applying in an incorporated band within the planting row area, opening possibilities of achieving yield responses to bentonite additions with reduced bentonite input. The amendment field trial in China demonstrated that the biggest impact on reducing soil acidity and increasing CEC were found to be with applications of 2.5 t/ha lime and 40 t/ha filter mud. In China, the effect of fire as a management tool in reducing stylo dominance has been demonstrated.
Investigations of 'organic', 'integrated' and 'agroforestry' farming systems' in Thailand showed significant increases in soil pH in the agroforestry and integrated farming systems. The agroforestry system resulted in significantly higher CECs at all depth increments to 70 cm. An acidity risk map to assess the risk of accelerated acidification associated with the production of upland cassava based systems in Northeast Thailand, has been developed.
In Thailand there has been considerable activity in transferring the results of research to the end users, largely through Professor Ruaysoongnern's involvement with farmer networks.

see final report