[Effects of N fertilization on winter wheat grain yield and its crude protein content and apparent N losses].

Field experiments were conducted at four sites in 2002 to study the effects of N fertilization on winter wheat yield and its crude protein content and apparent N losses. The results showed that at these sites, the N application rate for maximum grain yield was 0, 0, 79 and 118 kg x hm(-2), and that for maximum grain crude protein content was 122, 100, 127 and 174 kg x hm(-2), respectively. The residual nitrate-N content in 0 approximately 90 cm soil layer after harvest was linearly increased, while the apparent N losses during wheat growth season was exponentially increased with increasing N application rate. Under the N application rate for maximum yield, soil residual nitrate-N content ranged from 86 to 115 kg x hm(-2) and apparent N losses ranged from 2 to 32 kg x hm(-2), which were much lower than the residual nitrate-N content (106 approximately 168 kg x hm(-2))and apparent N losses(14 approximately 56 kg x hm(-2)) when the maximum grain crude protein content was achieved. The results showed that the maximum wheat grain yield and the environment effects of N fertilization could be harmonized by an optimized N application rate, but, if considering the importance of wheat grain protein, more research in the future should be needed.