In order to provide the information for N application in the wheat-maize rotation system under different soil fertility conditions,we selected the Kaifeng Baliwan(high soil fertility level),Zhengzhou(medium soil fertility level) and Kaifeng Shuidaoxiang(low soil fertility level) as the experimental sites to investigate the effect of nitrogen(N) application rates on photosynthetic characteristics and yield of winter wheat.Four different N fertilizer rates were used in the field experiments(wheat growing season:0,180,240 and 300 kg·hm-2;maize growing season:0,225,300 and 375 kg·hm-2,respectively) at the three sites.The results indicated that N application significantly increased photosynthetic rate,chlorophyll content,total N content and Rubisco activity by 22.4%-183.3%,37.9%- 306.2%,49.6%-359.3% and 27.4%-59.5%(average value of N180,N240 and N300) compared to non-N application,respectively. The increase rates of yield were different after N application at three fertility levels,10.8%-54.9% for high fertility soil, 125.3%-165.8% for medium fertility soil,and 63.3%-288.2% for low fertility soil compared to that under N0 treatment. When the experimental progressed three years,the wheat yield was increased by 36.1%(2014-2015),136.4%(2014-2015) and 288.2%(2016-2017) in high,medium and low fertility soil under the N treatments compared to that under N0 treatment,respectively. This suggests that the effect of N application on wheat depended on soil fertility. In high fertility wheat field,the basic soil fertility is high,and the contribution of soil to yield is large,but the dependence on nitrogen fertilizer is low,and thus the effect of nitrogen application on yield increase is not obvious. From the perspective of yield components,the yield from low yield to medium yield mainly depends on the increase of panicle number,and from medium yield to high yield mainly depends on the increase of grain number per panicle. Therefore,in order to get full effect of N fertilizer on yield increase,in low fertility wheat field,a small amount of nitrogen should be applied several times; in medium fertility wheat field,nitrogen should be stabilized,mainly to promote panicle number,with nitrogen application rate of 240 kg·hm-2; in high fertility wheat field,attention should be paid to nitrogen control,mainly to increase grain,with nitrogen application rate of 180 kg·hm-2. |