Effects Of Irrigation On Rules Of Field Water Consumption And WUE Of Winter Wheat

The effects of irrigation on rules of field water consumption, WUE, and yield were studied with high yield winter wheat cultivar 93-52 in water balance experiment and water-troughed experiment of Yucheng ecological station of CAS in 2001-2002. The results were as follows:1 The property of water requirement for winter wheat and the effects of irrigation on rules of field water consumptionThe property and amount of water requirement for crop are important basis of irrigation schedule and its reasonable allocation. The amount of water requirement for winter wheat was about 377mm, which was measured by Lysimeter under sufficient water supply. The average of Kc was 0.72, changing from 0.12 to 1.47 during the whole growth stages, and getting its maximum value (Kc>1) on milky filling stage which was the fastigium of water requirement for winter wheat. The jointing stage when Kc was only about 0.72 was the sensitive stage for water stress of winter wheat. The changes of soil moisture mainly happened in 0-120cm soil layer. Irrigation had considerable effects on 0-60cm soil layer, and could supply water for winter wheat about 15 days to 20 days. Field water consumption increased with the increase of irrigation, but the ability of water supply from SMBS decreased, which showed in the reduction of water supply amount, ascent of soil water supply layers and shortening of water supply duration. At last, the efficiency of SMBS utilization descended.Field water consumption (Evaportranspiration, ET) consists of crop transpiration (T) and soil evaporation (Es). Under sufficient water supply (Lysimeter experiment), Es was about 132.2mm, 32.7 percent to ET. Theaverage of T/Es during the whole stages was about 2.06. The maximum of it appeared in Flag stage was about 7-8, and its minimum appeared in winter was close to zero. Strong effects of irrigation on T/Es appeared: irrigation reduced the value of T/Es as well as increased ET, which means the ratio of Es to ET increased. This was one of the important reason for the decreasing of WUE caused by irrigation.2 The effects of irrigation on field water consumption, yield, and WUE of winter wheat The yield of winter wheat changed among different phases with the increase of field water consumption caused by irrigation, and the key reason was the variety of WUE. We introduced the concept of marginal water use efficiency (MWUE) and elasticity of water production (EWP) and discussed three phases of yield and WUE: when ET was less than 293.3mm, it was the first phase where WUE increased and yield was low; when ET was more than 293.3mm but less than 412.5mm, it was the second phase where WUE descended and yield was higher. When ET exceeded 412.5mm, it was the third phase where WUE was low and MWUE was less than zero. In the third phase, increasing irrigation would not benefit yield. The partition of three phases offered an important basis for reasonable allocation of irrigation water resources.There was a close relationship between three levels of WUE (leaf level, population level and yield level). The key reason of the changes of WUE of population level caused by irrigation was the changes of WUE in leaf level. WUE of yield level was determined by the combination of WUE of population and HI: with the increasing of field water consumption or irrigation, the WUE of population and HI had a contrary changes, which induced a lower WUE of yield when field water consumption was too low (less than 200mm) or too high (more than 400mm) and a higher value of WUE only when field water consumption was proper (about 293mm).Comparing with the three levels of WUE, the leaf level had a great difference from yield level, and was difficult to apply to practice. The yieldlevel had close relation to practice conditions, but it only had an average meaning, and did not revealed the dynamic relationship between yield and WUE. The WUE of population revealed the dynamic changes of WUE, and it was a better index to study the relationship between crop production and field...