The influence of rotation systems on long-term trends in wheat yield

Abstract

The wheat yield trends of six rotation systems were examined over the 29-year period 1940-1968. The multiple regression model used incorporated variables to minimize the effect of climatic fluctuations and trends. All the rotation systems examined showed positive, almost linear, yield increases over the first 19 years (1940-1958). Over the final 10 years (1959-1968) those systems including a pasture phase continued to show a linear yield increase; other three-course systems (fallow, wheat, stubble crop) showed a less than linear yield increase; while the two-course system (fallow, wheat) showed a 22% yield decline. Possible factors influencing the yield trends are briefly discussed.