The Influence of Rainfall on the Yield of Wheat in South Australia

Abstract

The relationship between the yield of wheat and seasonal rainfall in S. Australia has been determined. The period chosen for examination was 1896-1941 and the analysis extends to practically the entire wheat belt of the State, all major soil groups and variants of climatic conditions within the area being represented. Yield was assessed using the hundred, which has an avg. area of approx. 118 sq. miles, as the basic territorial unit. Seasonal weather was represented by the rains in 3 subdivisions of the growing period of the crop, and these were taken as independent variates in an analysis by multiple regression. The regression of yield on rainfall, when considered as a function of time, takes a mathematically simple parabolic form with a maximum in winter and zeros in autumn and spring or early summer, and the coeffs. obtained provide a clear demonstration of the sub-optimal character of avg. seasonal rainfall over most of the season and almost throughout the wheat belt. The conclusions drawn from the general survey are substantiated by analyses of a limited number of exact records.