This project replaces an earlier ACIAR initiative (Project 8328). It consists of an integrated series of laboratory, greenhouse and field studies of sulfur and phosphorus management of crops. It is designed to improve the efficiency and reduce costs of fertilisers used in upland and lowland cropping systems in Southeast Asian and Australian agriculture. A second focus is the provision of information, outlining where sulfur and phosphorus are required and in what quantities, to assist government decision-makers in Indonesia, Malaysia and Thailand.

The major objectives are: 1) to investigate management options that will increase the efficiency of utilisation of sulfur added in fertilisers and crop residues; 2) to monitor the contribution of sulfur and other nutrients from inputs via rainfall and irrigation waters; 3) to identify areas of sulfur deficiency, primarily in upland crops, and to develop a sulfur management recommendation package for particular soil/crop/climate regimes. The first two objectives are closely linked, and the third will arise as a consequence of information obtained in the first two.

The project consist of three subprojects.

Subproject A is entitled 'Sulfur and Phosphorus Management for Upland and Lowland Crops'. The work in this section entails studies of sulfur from different sources and will be in Thailand, Indonesia and Malaysia. Glasshouse experiments at Armidale, Australia will compare different methods of placement of sulfur and phosphorus and determine the most suitable time for sulfur application. Results will be measured by plant yield, nutrient uptake and nutrient leaching.

At Ubon, Thailand, scientists will study the availability of sulfur from crop residues and ask to subsequent crops, using 35S labelled residues. A complementary glasshouse experiment will take place at the Universiti Pertanian Malaysia.

New techniques for using phosphorus isotopes are now available, and will be used to trace the origins of phosphorus available to the plant, and thus to estimate the amounts of additional phosphorus needed by plants.

Subproject B Work will continue at the network of sites throughout Thailand, Malaysia and Indonesia, collecting data on nutrient availability from rainfall and irrigation water. it is also proposed to collect rainfall data from the FAO Sulfur Network sites in Southeast Asia and to establish a network of sites throughout Australia for comparative studies. The University of New England at Armidale will evaluate the contribution of sulfur in irrigation water.

Subproject C will involve development of a model for sulfur, based on data generated from the first project, which traced the transformation of sulfur in soils, the fate of sulfur applications and nutrients balances. A model of carbon/nitrogen/sulfur/phosphorus cycling, developed at the University of New England, will form the basis of the sulfur model.

Also, sulfur fractions measured in a range of soil extractants will be correlated against measured sulfur uptake and crop growth.

The research program is aimed at identifying areas of both deficients and excessive use, resulting in increased efficiency of fertiliser application. Farmers should increase their production efficiency, leading to marked gains in profit, and national governments should save on foreign exchange through reduced fertiliser imports.