| Abstract: | Data from 16 wheat growers and 18 barley growers in South East England were investigated for changes in variability of production and yield between the periods 1964-74 and 1975-84. Sixteen per cent of the increase in variability of wheat production was due to changes in yield variances and covariances. The increase in variability of barley production was not statistically significant. Variability of yield increased for both wheat and barley. Wheat yields became more positively correlated between farms, but barley yields did not. The results for wheat were consistent with the hypothesis of an increase in the number of controlled factors in the production process. Particularly important was thought to be the use of fungicides in the control of many cereal diseases. Increased heterogeneity of the barley crop may have contributed to the decline in the number of between-farm correlations for that crop. |
