AN IMPROVED WATER-USE EFFICIENCY FOR WINTER-WHEAT GROWN UNDER REDUCEDIRRIGATION

Single irrigation, compared to the conventional four or five irrigatio ns, has been practised in northern China on winter wheat on a relative ly large scale since 1991. In a field study, irrigation was reduced fr om normally four times (I-4, 4x75 mm) to one (I-1, 75 mm at the end of the second internode elongation) in an area with an annual rainfall o f about 600 mm. A control without irrigation (I-0) was also included. Late sowing and early soil drying at seedling stage resulted in a rela tively deep root system. Leaf area index, the size of upper leaves and the length of base internodes were also significantly reduced underI( 1), but kernel number per panicle was not reduced, suggesting that the development of inflorescence was not disrupted. During the active gra in-filling stage, it was found that leaf water potential under I-1 was maintained similar to that of I-4, while daytime stomatal conductance was substantially reduced. Leaf temperature was increased, indicating an inhibited leaf transpiration. Early senescence was induced in I-1 and I-0 crops and resulted in a substantially lower kernel weight. Alt hough the grain yield of I-1 was reduced by about 15% from I-4, the wa ter-use efficiency (WUE) for total water consumption was increased by 24-30%. Single irrigation can potentially make wheat cropping sustaina ble in this area in terms of water usage and prevent further depletion of the underground water resource. Explanations for the small or zero reduction in yield are: (1) the encouraging development of a deep roo t system that enabled the plants to use more water at depth (below 1 m ), which is recharged annually by the relatively high summer rainfall. (2) A large portion of root system in the drying soil and its induced shoot physiological changes, that is, reduced leaf expansion and stom atal conductance, which helped the plants to establish a better canopy structure with a much reduced water consumption. (3) An improved harv est index. (C) 1998 Published by Elsevier Science B.V. All rights rese rved.