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The Agricultural Preoduction Systems Simulator (APSIM) suite of models was used to predict dynamics in water and nitrogen in soil, as well as the growth and yield of sequential srops of wheat ands barley in pasture-wheat-barley rotations, between 1995 and 1997 at Rosewirthy, South Australia. The NWHEAT model satisfactorily predicted above ground dry matter, leaf area index and grain yields for both crops in rotations with wither grassy (Grass) or medi (Medic) pastues, including the lack of significant response of yiled to nitrogen fertiliser applied to whaet at sowing. Simulation data for soil water, from SOILWAT2, was consistent with measured data. Simulation with SOILN2, however, largely underestimated soil nitrogen, due to excessive uptage by the simulated wheat during the season when nitrogen was abundant and water supply readily available. Thus, the soil nitrate had to be reset at sowing for the following barley crop; simulated soil nitrate agreed with the measured data in this season when this nutrient was low. For most variables fo crop growth and soil water, the simulated data was mostly within 2 standard errors of the measured means. Prediction of grain protein was underestimated in all cases,including where nitrogen in the shoot was overestimated. This was possibily due to inadequate remobilisation of nitrogen fromt he staw and roots to the grain by the simulated crop. This study demostrated the capability fo APSIM to predict growth and grain yield of wheat and barley, as well as the associated dynamics of soild water int he main cereal belts of South Australia.

The Agricultural Preoduction Systems Simulator (APSIM) suite of models was used to predict dynamics in water and nitrogen in soil, as well as the growth and yield of sequential srops of wheat ands barley in pasture-wheat-barley rotations, between 1995 and 1997 at Rosewirthy, South Australia. The NWHEAT model satisfactorily predicted above ground dry matter, leaf area index and grain yields for both crops in rotations with wither grassy (Grass) or medi (Medic) pastues, including the lack of significant response of yiled to nitrogen fertiliser applied to whaet at sowing. Simulation data for soil water, from SOILWAT2, was consistent with measured data. Simulation with SOILN2, however, largely underestimated soil nitrogen, due to excessive uptage by the simulated wheat during the season when nitrogen was abundant and water supply readily available. Thus, the soil nitrate had to be reset at sowing for the following barley crop; simulated soil nitrate agreed with the measured data in this season when this nutrient was low. For most variables fo crop growth and soil water, the simulated data was mostly within 2 standard errors of the measured means. Prediction of grain protein was underestimated in all cases,including where nitrogen in the shoot was overestimated. This was possibily due to inadequate remobilisation of nitrogen fromt he staw and roots to the grain by the simulated crop. This study demostrated the capability fo APSIM to predict growth and grain yield of wheat and barley, as well as the associated dynamics of soild water int he main cereal belts of South Australia.