Consumption Characterisitics And Effective Use Of Available Soil Water Stored At Planting By Winter Wheat

It is well know that the agricultural water resource is very limited in North China, especially during winter wheat growth period. The sufficient use of available soil water at planting (ASWp) stored in the deep soil layer is an effective measure to improve water use efficiency (WUE).The field and plots experiments were conducted at the Gucheng Agrometeorological Experimental Base of China Meteorological Administration from September 1997 to June 2000. The Results showed the follows:Under the normal ASWp condition and no water supply, the consumption of ASWp lasts until the late grain filling period, and the average wheat yield is about 1160kg/hm2. The consumption ratios of ASWp (Re) in the 0~50cm layer in all treatments are over 85%. In the deeper portion of the soil profile (below 50cm), Re decreases not only with the deepening soil, but also decreases with the decrease of ASWp level resulted from the unsuccessful development of the root system. The low precipitation (70.6mm) did not affect Rc in the 0~50cm soil profile. During sowing~jointing period, the water supply rate in all layers were higher than those during jointings-maturing period.The different ASWp influenced root system of winter wheat evidently. Enough ASWp can promote the ability that root system absorbs water and nutrient from soil layer, improve the WUE of soil moisture, reduce soil water remained in soil at harvest time, extend the capacitance of soil reservoir, let the soil reservoir save up more and more precipitation of flood season, bring into play the regulation function of soil reservoir. The correlation between the growth of leaf and ASWP was very evident, there is a prominent relationship of power function between ASWp and LAI. The influence of ASWP on total spikes, grains per ear, thousand grain weight and over-ground total biomass are also evident, ASWp has quadratic relationship with grain weight. The optimal ASWp 85.37% (relative soil moisture ) was obtained from the formula.The fertilizing depth of 20~40cm can strengthen the growth of root system in mid-layer and deep-layer, therefore extend the space where wheat may absorb more water and nutrient. It contributes to effectively make use of the water in deep soil layer, which brought into play the regulation function of soil reservoir to improve the water use efficiency and yield of winter wheat.As a result of water deficit, dry matter and root length density in the upper soil layer were reduced, and there was more root dry matter in the deeper soil layer. This resulted in greater use of water from the deeper soil layers and increased water use efficiency of the ASWp. This improved the water use efficiency of irrigation and soil water.In conclusion, sufficient ASWP and limited added water at jointing stage are more effective than sufficient ASWp and limited water split between the greening period of early spring and at jointing stage. The water supply scheme of having a high level of ASWP at time of planting supplemented by addedwater at jointing stage is an effective approach to the efficient use of limited water resources and improving WUE.