Nitrogen fertilizer and wheat in a semi-arid environment. 2. Climatic factors affecting response

Abstract

The response of Gabo wheat to nitrogen fertilizer at 52 sites in the wheat growing areas of South Australia during 1956-61 was examined in relation to climatic factors by a stepwise multiple regression analysis using a computer. The ten dependent variables were the linear and quadratic coefficients obtained by fitting orthogonal polynomials to response curves of various parameters (grain yield, grain + straw yield, harvest index, grain nitrogen percentage, and grain nitrogen yield) to applied nitrogen at each of the 52 sites. The 23 independent variables were the amounts of rainfall and evaporation during the growing period, maximum and minimum temperatures and estimates of high temperature stress during spring and amount of rainfall immediately after sowing at each site. The climatic variables examined explained 46.5, 64.3, and 64.3 per cent of the variation in the response to nitrogen fertilizer of grain yield, grain + straw yield, and grain nitrogen yield respectively. The positive effects of increasing amounts of winter rainfall on yield response to applied nitrogen were marked. On the other hand, the negative effects of high maximum temperatures in the latter part of the growing period, particularly during October, on yield response were also evident.