OZCOT - A SIMULATION-MODEL FOR COTTON CROP MANAGEMENT

A cotton crop simulation model was constructed by linking a simple temperature-driven model of the fruiting dynamics to the widely used Ritchie (1972) soil water balance model. The function describing the processes in the fruiting model were made sensitive to solar radiation, water and nitrogen stress and water logging. A leaf area ea generator, a boll growth model and an elementary nitrogen model were added. The model was validated against six data sets from agronomic experiments over a period of 30 years covering the range of Australian cotton growing regions from 15 degrees to 34 degrees S. The model responded to climatic and agronomic (irrigation regime, nitrogen fertiliser rate and sowing date) variables at all sites, and without bias at 5 out of 6; a difference in soil type probably caused the bias at one site. Decision support needs dictated development of the model, which is no more complex than needed to supply information for management decisions. The project demonstrates that such a 'top down' approach can produce a simple yet powerful simulator.