Agronomic and Physiological Responses of Soybean and Sorghum Crops to Water Deficits I. Growth, Development and Yield

Abstract

The aim of the work reported in this series of four papers was a better understanding of crop response to water deficits in an area where water available for irrigation is limited. In part I, data on the effect of frequency of irrigation, applied post-flowering, on the growth, leaf area development and yield of soybean, cvv. Bragg and Ruse, and sorghum, cv. TX610, are evaluated. Sorghum outyielded both irrigated and rainfed soybeans (5400 versus 2800 and 1800 kg ha-1, respectively). Soil water deficits during pod filling in soybeans caused early leaf death and cessation of pod filling, thus decreasing yield. Irrigation at approximately 90 mm and 135 mm soil water deficit resulted in similar yields. In sorghum and in Ruse soybeans, there was a significant (17-25%) loss in stem dry weight during grain filling, which may have been caused by the relocation of stored assimilates. In Bragg soybeans, only the rainfed plants had a loss in stem dry weight during grain filling. Differences in crop dry weight occurred later than predicted by photosynthesis measurements. Several factors could have contributed to this discrepancy, and we highlight the need for a greater understanding of the contribution from lower leaves and also of the factors affecting the storage and remobilization of reserve assimilates during grain filling.