不同轮作模式下氮肥用量对土壤有机氮组分的影响

Effects of Nitrogen Application Rate on Fractionation of Soil Organic Nitrogen Relative to Crop Rotation Mode

通过三年六季的田间定位试验,对比研究了水旱轮作(水稻/油菜)和旱地轮作(棉花/油菜)下氮肥用量对土壤有机氮含量及其组分的影响。结果表明,经过三年轮作后,周年轮作氮肥投入超过300 kg hm^(-2)(以纯氮计,下同)的处理0~20 cm土壤全氮含量明显增加。与不施氮处理相比,周年氮肥用量为300 kg hm^(-2)和375 kg hm^(-2)水旱轮作处理0~20 cm土壤全氮含量增加了13.6%~23.5%,而旱地轮作处理则增加了15.0%~23.0%,土壤酸解态氮含量增加是土壤全氮变化的主要原因。两种轮作模式下土壤酸解态氮含量无显著差异,但土壤酸解态氮各组分的变化却不相同。水旱轮作中酸解铵态氮增加的比例(33.8%)低于旱地轮作(53.9%),但其酸解未知态氮含量增加的比例(36.0%)高于旱地轮作(16.6%)。综上所述,周年氮肥合理施用能明显提高土壤有机氮含量,水旱和旱地轮作下土壤酸解态氮库各组分变化差异明显。根据不同轮作模式下土壤有机氮库转化特点,优化氮肥施用对于提高作物产量和氮肥利用率具有重要意义。

A 3 a field experiment,consisting of 6 croppings,was conducted to investigate effects of N fertilizationon content and fractionation of soil organic N relative to N application rate and crop rotation mode,paddy/upland（rice/rapeseed,RR）rotation and upland（cotton/rapeseed,CR）rotation. Results show that after the 3 years of crop rotations cultivations,soil total N content in the 0~20 cm soil layer increased remarkably in plots more than 300 kg hm^-2 in N input. Compared with CK（No N fertilization,N0-0）,soil total N content increased by 13.6%~23.5% and 15.0%~23.0%,respectively,in the treatments 300 kg hm^-2 and 375 kg hm^-2 in N application rate under either RR or CR rotation. The increase in soil total acidolysable N content accounted for most of the increase in soil total N. Although no significant difference in soil total acidolysable N content was observed between plots under RR and CR rotations,fractionation of the soil acidolysable N varied between plots. The proportion of soil acidolysable ammonium N increased by 33.8% in the plots under RR rotation,much lower than that（53.9%）in the plots under CR rotation,but the increment of unidentified soil acidolysable N in proportion was higher in plots under RR rotation（36.0%）than that（16.6%）in the plots under CR rotation. To sum up,reasonable N fertilization may significantly increase soil organic N content. Fractionation of the soil organic N pool varies sharply between plots under RR and CR rotations. It is,therefore,of important significance to optimize N fertilization for high crop yield and high N utilization efficiency in the light of the characteristics of soil organic N transformation under different rotation systems.