渭北旱地冬小麦监控施氮技术的优化

【目的】氮素是限制旱地小麦增产的主要养分因子，不合理施氮不仅难以增加小麦产量，还会造成土壤剖面硝态氮累积、氮素损失增大和氮素利用效率降低。优化氮肥用量推荐方法、解决旱地小麦不合理施氮问题，对旱地小麦可持续生产有重要意义。【方法】基于平衡土壤氮素携出，以稳定作物产量、培肥土壤和调控硝态氮残留为目标，对现有的土壤硝态氮监控施氮方案（施氮量=作物目标产量需氮量+肥料氮素损失量+收获/播前土壤硝态氮安全阈值（55.0/110.0 kg?hm-2）-环境氮素投入量-秸秆还田带入氮素量-种子带入氮素量-生长季土壤氮素矿化量-收获/播前1 m土壤硝态氮）进一步优化，得出公式：施氮量=作物目标产量需氮量+收获/播前土壤硝态氮安全阈值（55.0/110.0 kg?hm-2）-收获/播前1 m土壤硝态氮。应用这一方法在西北典型旱地冬小麦种植区渭北旱塬两年6县30个地块布置田间试验。【结果】在该区域由于不合理施氮或没有规范的氮肥推荐方法，不同试验地播种前1 m土壤累积硝态氮积累量变化较大，介于34.2-708.4 kg?hm-2，平均为165.2 kg?hm-2，其中有17块在小麦播种前超过110 kg?hm-2。优化后的监控施氮技术确定的小麦氮肥用量介于30.0-247.3 kg?hm-2，平均为128.4 kg?hm-2，较农户习惯氮肥用量（171.6 kg?hm-2）减少25.2%。监控施肥和农户习惯施肥的小麦籽粒产量平均分别为5 658和5 489 kg?hm-2，籽粒氮含量为20.8和20.3 g?kg-1，两者均无显著性差异。监控施肥能够显著提高氮素利用率和氮肥偏生产力，较农户习惯施肥分别提高24.0%（由46.3%提高到57.3%）和130.1%（由34.9 kg?kg-1提高到80.3 kg?kg-1）。收获时，农户习惯施肥0-100 cm土层的硝态氮残留量介于17.4-203.4 kg?hm-2，地块间变幅大，平均为70.6 kg?hm-2；而监控施肥介于15.6-113.9 kg?hm-2，平均为51.4 kg?hm-2，稍低于预期的55 kg?hm-2的目标。在降水较多的夏闲期，优化的监控施氮技术可使0-100 cm土层的硝态氮淋失减少47.9%。【结论】优化后的旱地冬小麦监控施氮技术可以方便地确定和有效调控氮肥用量，稳定小麦籽粒产量，提高氮素利用效率和氮肥偏生产力，降低土壤硝态氮残留和淋溶。

Optimization of Nitrogen Fertilizer Recommendation Technology Based on Soil Test for Winter Wheat on Weibei Dryland

【Objective】Nitrogen (N) is the main nutrient factor limiting wheat yield increase on dryland. Unreasonable application of N fertilizer not only makes it difficult to increase wheat yield, but also leads to increased nitrate N (NO₃^--N) residual in soil, enhanced N losses, and reduced N use efficiency. Therefore, it is of great significance to optimize the method of N fertilizer recommendation and solve the problem of unreasonable N fertilizer application for the sustainable production of wheat on dryland.【Method】 Based on balancing N output from soil by crop production and aimed at stabilizing crop yield, improving soil fertility and regulating NO₃^--N residual, the present method for Recommendation of N fertilizer Based on Monitoring NO₃^--N in 1.0 m Soil (RNBM, N application rate = N required for the target crop yield + Fertilizer N losses + Safety threshold of NO₃^--N in 1 m soil at harvest or before sowing (55.0/110.0 kg·hm^-2) - N input from environment - N input with straw retention - N input with seed - Soil N mineralization during winter wheat growing season - NO₃^--N in 1m soil at harvest or sowing) was optimized to be as: N application rate = N required for the target crop yield + Safety threshold of NO₃^--N in 1 m soil at harvest or before sowing (55.0/110.0 kg·hm^-2) - NO₃^--N in 1 m soil at harvest or before sowing. Using the optimized RNBM, two-year field experiments on 30 plots were carried out in six counties on Weibei Arid Tableland in Shaanxi Province. 【Result】 As the result of chronically unreasonable application of N fertilizer due to the lack of normative N fertilizer recommendation methods, it was found that in this region, the NO₃^--N residual in 1.0 m soil at sowing varied largely among different sites from 34.2 kg·hm^-2 to 708.4 kg·hm^-2, with the average to be 165.2 kg·hm^-2 and 17 of 30 sites higher than 110.0 kg·hm^-2. Nitrogen application rates determined by the optimized RNBM ranged from 30.0 kg·hm^-2 to 247.3 kg·hm^-2, with the average of 128.4 kg·hm^-2, which was 25.2% lower compared to that (171.6 kg·hm^-2）of the farmer’s practice (FP). The averaged wheat grain yield by the optimized RNBM and FP was respectively 5 658 kg·hm^-2 and 5 489 kg·hm^-2, grain N concentration was 20.8 g·kg^-1 and 20.3 g·kg^-1, showing no significant difference. Compared to FP, the optimized RNBM significantly increased N use efficiency (NUE) and partial fertilizer productivity of N (PFPN) by 24.0% (from 46.3% to 57.3 %) and 130.1% (from 34.9 kg·kg^-1 to 80.3 kg·kg^-1), respectively. At harvest time, NO₃^--N residual in 1.0 m soil under FP was found averaged to be 70.6 kg·hm^-2 (17.4 kg·hm^-2 to 203.4 kg·hm^-2), and that under the optimized RNBM was only 51.4 kg·hm^-2 (15.6 kg·hm^-2 to 113.9 kg·hm^-2), a little bit lower than the expected target of 55.0 kg·hm^-2. During the rainfall intensive summer fallow, NO₃^--N leached from 0 to 100 cm soil layer under the optimized RNBM was observed to be reduced by 47.9% compared to the FP. 【Conclusion】Therefore, the optimized RNBM is able to be flexibly used to determine and effectively regulate the N fertilizer rate, stabilize wheat grain yield, increase NUE and PFPN, and minimize NO₃^--N residue and leaching in dryland soil.