The Impacts of Supplemental Irrigation Based on Soil Moisture Measurement and Nitrogen Use on Winter Wheat Yield and Nitrogen Absorption and Distribution

Based on split plot design method of field test, the impacts of supplemental irrigation based on soil moisture measurement and nitrogen use on winter wheat yield and nitrogen absorption and distribution were studied. Supplemental irrigation had three levels: 60%（W1），70%（W2） and 80%（W3） of the targeted relative water content at 0-40 cm of soil layer during jointing period of winter wheat. Nitrogen fertilization had three levels: not using nitrogen （N0）, using pure nitrogen of 195 kg/hm2（N195） and 255 kg/hm2（N255）. Results showed that: (i) different supplemental irrigation and nitrogen fertilization significantly affected plant height and leaf area of winter wheat during key growth period. Under the same supplemental irrigation treatment, both plant height and leaf area of winter wheat showed as N255> N195> N0（P <0.05）. Plant height in N195 and N255 treatments was significantly higher than that in N0 treatment, but there was not significant difference between N195 and N255（P>0.05）. Under the same nitrogen fertilization, plant height in W2（569.4 m3/hm2） and W3（873.45 m3/hm2） treatments was significant higher than that in W1（265.2 m3/ hm2）, but there was not significant difference between W2 and W3（P>0.05）. It illustrated that excessive nitrogen fertilization and supplemental irrigation did not significantly affect plant height and leaf area of winter wheat. （ii）Under the same nitrogen fertilization level, yield increase effect of winter wheat by supplemental irrigation showed a declining trend with nitrogen application amount increased. It illustrated that nitrogen fertilization and supplemental irrigation had certain critical values on the yield of winter wheat. When surpassing the critical value, the yield declined. When nitrogen fertilization amount was 195 kg/hm2, and supplemental irrigation amount was 70% of field moisture capacity （569.4 m3/hm2）, the highest yield 8500 kg/hm2 could be obtained. (iii) During mature period of winter wheat, nitrogen accumulation amount of plant treated by nitrogen was significantly higher than that not treated by nitrogen （P<0.05）. But under the treatments of W2 and W3, nitrogen accumulation amount in N255 significantly declined when compared with N195（P<0.05）. Especially under W3（873.45 m3/hm2）level, nitrogen accumulation amount in N255 was even lower than N0. Under the treatments of N0 and N195, nitrogen accumulation amount of plant significantly increased with supplemental irrigation increased （P<0.05）. But under N255 treatment, there was not significant difference （P>0.05）. It illustrated that moderate supplemental irrigation and nitrogen fertilization could improve nitrogen absorption ability of winter wheat, but excessive supplemental irrigation and nitrogen fertilization were not favorable for plant’s nitrogen absorption. (iv) Although the increase of supplemental irrigation during jointing period improved nitrogen absorption ability of winter wheat and promoted winter wheat absorbing more nitrogen, it inhibited nitrogen transferring and distributing to seed. Comprehensively considering growth condition of winter wheat and nitrogen risk condition, it is suggested that nitrogen application amount was 195 kg/hm2, and supplemental irrigation reached 70% of field moisture capacity (569.4 m3/hm2), which could be as the suitable water and fertilizer use amounts in the region.