Productivity and stability of grain yield in maize and sorghum as affected by rotational cropping systems in the north western Free State

Abstract

The beneficial effects of crop rotation have long been researched and recognised in the world. Research results on crop rotation in South Africa are limited. The objective of this study was to determine the effect of crop rotation with groundnut, soyabean or sunflower on the yield and yield variability of first and second year maize and sorgbum on a sandy soil in the north western Free State. The 7-year and 4-year study for maize and sorghum respectively, was managed for optimal production. The yield of first year maize after groundnut was 16% and after soyabean 12% higher than the yield of monocropped maize, while the yield of maize after sunflower was unaffected. The yield of second year maize was unaffected by crop rotation. Yield variability was slightly higher for first year maize (coefficient of variation = 54%) than for the second year and monocropped maize (coefficient of variation = 46%). However, the probability of obtaining a yield below a disaster target level with first year maize, is equal to or less than that of monocropped maize depending on the level of the disaster target yield. First year sorghum yields were unaffected by crop rotation. The yield of second year sorghum after groundnut and sunflower was lower than that of first year and monocropped sorghum. Yield variability for second year sorghum was also slightly higher than that of the first year and monocropped sorghum. Groundnut yield was higher after maize than after sorghum, while soyabean yield was higher after sorghum than after maize. The yield of sunflower was unaffected by crop rotation although the yield variability was higher after sorghum than after maize.