Effects of Nitrogen Amount on Wheat Yield and Nitrogen Absorption Amount in Wheat-cotton Intercropping System

In wheat-cotton intercropping system 7 nitrogen fertilizer treatments(45,90,135,180,225,270 and 315 kg/hm2) were designed to study the effects of nitrogen amount on SPAD of flag leaves, dry weight accumulation of wheat plants,nitrogen absorption amount at booting stage,and nitrogen absorption amount in grains, wheat yield and yield components at harvest stage using no nitrogen as control.The results showed that with the increasing of nitrogen application,SPAD of flag leaves,dry weight of wheat plants, nitrogen absorption amount of plants increased, nitrogen absorption amount of grains, spike number per area, grain number per spike, 1 000 grain weight and yield first increased and then decreased,the yield reached maximum with the 225 kg/hm2 nitrogen amount,then 180 kg/hm2 followed.The index value of 7 nitrogen treatments were all higher than CK,with nitrogen amount of 180-315 kg/hm2 which were all significantly higher than that of others except dry weight.Nitrogen agronomic efficiency and production efficiency of nitrogen fertilizer treatment were all lower than that of CK, which was decreased with the increasing of nitrogen amount.Nitrogen agronomic efficiency of 270 and 315 kg/hm2 nitrogen amount significantly lower than others,andni trogen production efficiency of which was also lower than that of 45-180 kg/hm2 nitrogen amount.Comprehensive consideration of production and cost,the suitable nitrogen fertilizer rate was 180-225 kg/hm2 in wheat season of wheat-cotton intercropping system.