Relations between yield of wheat, soil factors, and rainfall

Abstract

Data have been collected from wheat plots in long-term rotation experiments on a red-brown earth at Adelaide, South Australia. Measurements were made of the apparent density and total nitrogen status of' the surface soil and of seedling establishment. Variation in grain yield, as well as grain yield response to applied nitrogenous fertilizer, was assessed in relation to these factors both within and between seasons. In particular, soil and plant responses to the amount of rainfall occurring just after sowing hare been examined. It has been shown that there are marked seasonal changes in apparent density associated \ d h the mount of rainfall occurring in the month following sowing. These seasonal changes in apparent density are accompanied by a reduction in seedling establishment and a depression of crop grain yield in years of high post-seeding rainfall. The results suggest that a large part of the reduction in yield in excessively wet seasons on unstable soil.; like the red-brown earth may be ascribed to poor physical conditions of the soil, and not predominantly to the leaching of nitrate.