Berndt, R. D. and White, B. J., 1976. A simulation-based evaluation of three cropping systems on cracking-clay soils in a summer-rainfall environment. Agric. Meteorol., 16: 211--229.
Water balance simulation techniques were used to evaluate three cropping systems under a range of soil-climatic environments. The systems were assessed on economic and conservation grounds using crop yield and surface run-off estimates.
A soil water balance model was developed and tested for the study region --the Darling Downs in southern Queensland. The model explained 87--96% of the observed variation in stored soil water in test runs. Relationships between grain yield and an index of crop water supply were established which explained 76% of the observed variation in wheat and sorghum farm yields. These relationships were used to derive yield estimates of simulated crops under two conventional cropping systems --continuous wheat and continuous sorghum --and a more flexible system, opportunity cropping.
Annual income under each cropping system was determined using partial budgeting in an economic sub-model. The soil conservation impact was determined using surface run-off estimates from the model as indicators of soil loss. Three objectives were then used to assess the net benefits of the different management systems over time: to maximize net income, to minimize variability of income, and to minimize soil loss. The evaluation showed that, because of the climatic variation present, no one cropping system was optimum for the region. The opportunity cropping system considerably reduced estimated soil loss, but had an economic advantage only in the less arid, eastern part. Variability of annual income was much greater for the opportunity cropping system than for the monoculture systems. Fallow storage of rainfall for subsequent crop use was more important for wheat crops than for sorghum. Longer fallow durations to accumulate high levels of stored soil water in all seasons were not warranted, as the higher crop yields so produced did not compensate for the resultant fewer crops.