CHANGES IN CEREAL PRODUCTION AND YIELD VARIABILITY ON FARMS IN SOUTH EAST ENGLAND
研究了1964-74和1975-84两个时期英格兰东南部16个小麦种植者和18个大麦种植者的产量与生产变异性变化，发现小麦生产变异性增加部分源于产量方差和协方差变化，大麦变异性增加不显著。
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.