氮肥后移对土壤氮素供应和冬小麦氮素吸收利用的影响

采用田间试验研究了氮肥后移对土壤氮素供应和冬小麦氮素吸收利用的影响。结果表明，与农民习惯施氮（N 300 kg/hm2，基肥和拔节肥各占1/2）比较，氮肥后移处理（N210kg/hm2，基肥、拔节肥和孕穗肥各占1/3）在不降低小麦产量的同时，大大提高了氮肥利用率，且全生育期氮素表观损失极低。过量施用氮肥(N 300 kg/hm2)明显提高了60 cm以下土层硝态氮含量，增加了其向地下水淋溶迁移的风险。氮肥后移可提高小麦成熟期0-20cm土层硝态氮积累量，降低其在20-100cm土层的积累。基于冬小麦不同生育阶段的氮素吸收量而进行氮肥后移是可行的，氮肥后移可节省氮肥30%，是较为理想的施氮方式。

Effect of postponing N application on soil N supply,plant N uptake and utilization in winter wheat

Field experiment was carried out to investigate postponing N application on soil N supply, plant N uptake and utilization in winter wheat. Results obtained showed that, compared with farmers’ practice (N 300 kg/ha, 1/2 basal and 1/2 topdressing at jointing stage, respectively), postponing N application treatment (N 210kg/ha, 1/3 basal, 1/3 topdressing at jointing stage and 1/3 topdressing at booting stage, respectively) improved N use efficiency greatly, and minimized apparent N losses without grain yield losses. Excessive N application (N 300 kg/ha) increased NO₃^--Ncontent below 60 cm soil profile at different growth stage, which would result in high risk of NO₃^--Nleaching into underground water. Postponing N application increased nitrate accumulation in the soil of 0-20 cm and reduced nitrate accumulation in 20-100 cm soil profile. Therefore it was concluded that postponing N application based on plant N uptake at different growth stage is a feasible N management practice, and nitrogen fertilizer could be saved by 30% as compared with farmers’practice.