Completed The project is aimed at the needs of resource-poor agriculture in the semi-arid tropics for which nutrient constraints on crop growth are a major limitation to agricultural development. 1.)To develop a model for mine The influence of nitrogen and phosphate nutrition on crop production has been incorporated into the PARCH model. Using the data available from previous work, and that derived from a parallel NRI managed project the model has been tested and its performance found to be satisfactory. However, further independent testing is desirable. The model diskette and documentation are intended to make the methods available in a usable form. Initial feedback on these from potential users (via Cranfields PARCH evaluation visit in March 1996) is positive,. However, it is too early to judge the final impact of the project. The end product of the project will be a fully documented and usable model for crop growth in response to climate and soil chemical and physical conditions. This will be an extension of the existing PARCH model. A fully functional nitrogen and soil-organic matter sub model was developed, based on Wageningen work and the CERES models approach with careful consideration to the low-input nature of resource-poor agriculture. Preliminary comparisons with field data (provided by CSIRO & ICRISAT) were made and the results were encouraging. However the data was from relatively high-input trials and effective liaison with Reading (G Warren, Soil Science) was established so that data from their low-input trials in Kenya could be used for model evaluation. A simplified user input system was developed so that the model could be used (albeit with less accuracy) with limited soil parameter inputs.