水稻不同移栽密度的氮肥效应及氮素去向

利用15N示踪技术，研究不同移栽密度对水稻产量、氮肥吸收利用及其氮素去向的差异。结果表明，随移栽密度变大，水稻产量显著增加，穗粒数、结实率和千粒重降低，子粒与秸秆氮肥吸收量、肥料利用率及其残留量增加，而氮素损失降低。水稻所吸收的氮素约2/3来源于土壤氮，1/3来源于当季肥料施的氮。不同处理间，肥料利用率为16.69%～26.69%，氮肥残留率为17.12%～21.08%，有52.23%～66.19%的肥料损失。无论哪种密度下，肥料主要残留在0～20 cm土层中。密度为40 cm×40 cm时，0～20 cm土层氮素残留量高于50 cm×50 cm和30 cm×30 cm处理，为28.54 kg/hm2，占施肥量的12.97%；而在40～60 cm的土层的氮素残留量为7.34 kg/hm2，比50 cm×50 cm和30 cm×30 cm处理同层残留量降低了57.90～59.29%。

Nitrogen Utilization Efficitncy and Fate of Fertilizer under Different Transplanting Density

Field experiments were conducted to study rice yield, N uptake and fate by using 15N-urea labeling method under transplanting density of 30 cm×30 cm, 40 cm×40 cm and 50 cm×50 cm. The results showed that improvement of transplanting density significantly increased rice yield. Grain-panicle, seed setting rate and 1000-grain weight decreased with improvement of transplanting density. Absorption 15N-fertilizer by grain and straw of rice, nitrogen use efficiency and 15N-fertilizer residue was high at high density, but 15N-fertilizer loss was low. Under different density, N absorption by rice mainly came from soil. Almost 1/3 of the total N uptake by rice supplied by fertilizer, and 2/3 N came from soil. At different treatments, nitrogen use efficiency were 16.69%～26.69%, 15N-fertilizer residue ratio were 17.12%～21.08%, and 15N-fertilizer loss were 52.23%～66.19%. Residue 15N-fertilizer mainly distributed in 0～20 cm top soil. Under 40 cm×40 cm, the amounts of fertilizer residue in 0～20 cm top soil were higher than that of 50 cm×50 cm and 30 cm×30 cm. It was 28.54 kg/hm2, occupying 12.97% of the total applied fertilizer. Under 40 cm×40 cm, the amounts of fertilizer residue in 40～60 cm soil profile was 7.34 kg/hm2, and it was lower 57.90%～59.29%than that of 50 cm×50 cm and 30 cm×30 cm.