To make the OZCOT cotton crop simulation model more robust and versatile; enabling it to be used for decision support in a broader range of applications and situations. This involved five specific objectives: 1. Improve the water balance component of the model. particularly the parts dealing with water movement in the soil profile. by incorporating the CERES water balance subroutines. 2. 3. 4. 5. Incorporate the soil nitrogen subroutines from CERES to allow simulation of nitrogen and organic matter dynamics in the soil. Develop an explicit carbon balance for the model in which photosynthesis produces dry matter which is then partitioned between organs. In the past, carbon balance has been modelled implicitly by using "carrying capacity" (bolls supported per metre of row) as a surrogate for photosynthetic capacity. Develop subroutines to model the uptake and distribution of nitrogen within the cotton plant. This will allow the model to respond dynamically to nitrogen supply, introducing the capacity for consideration of tactical nitrogen issues. It is also a necessary interface for connection to the soil nitrogen sub-model. Collect data on key developmental parameters which characterise the differences in fruiting dynamics between cotton cultivars. These model parameters allow a degree of cultivar sensitivity in the simulation output. The data will be used to maintain the models relevance to current cultivars and to test the importance of variation in these parameters for simulation output