河西绿洲灌区玉米间作绿肥根茬还田的氮肥减施效应

  【目的】  明确玉米与间作豆科绿肥根茬还田生产方式在河西绿洲灌区的氮肥减施效应。  【方法】  玉米间作豆科绿肥，绿肥(针叶豌豆和毛叶苕子)地上部乂割做饲草根部还田，定位试验位于甘肃河西绿洲，始于2011年，至本试验取样时已进行了10年。试验共设8个处理，包括无绿肥根茬还田条件下后茬玉米不施肥对照，施常规量氮肥(N 375 kg/hm2)，只有针叶豌豆、毛叶苕子根部还田，以及根部还田配合常规氮肥量的80%、90%。于2020年玉米收获后测产，并测定了玉米秸秆和籽粒氮、磷、钾养分含量，同时分析了0—20 cm土壤有机质、速效氮磷钾含量及土壤氮库(全氮、有机氮、无机氮、颗粒态有机氮、可溶性有机氮、土壤微生物量氮)。  【结果】  与常规施氮肥相比，根茬单独还田降低了玉米产量；绿肥根茬配施80%、90%常规量氮肥处理之间的玉米籽粒产量没有显著变化，其中针叶豌豆配合80%常规量氮肥还显著增加了玉米产量7.6%；玉米地上部氮磷钾累积量略有增加，而籽粒氮、磷、钾养分累积量分别增加了31.7%～56.4%、37.8%～60.0%、61.7%～96.8%；玉米氮肥农学效率、偏生产力、氮素吸收效率和氮肥表观利用率均显著增加，以针叶豌豆根茬配施80%常规量氮肥处理的增加幅度最高，增加值分别为43.6%、34.5%、107.9%、35.8个百分点 (P<0.05)。采用改进的内梅罗指数法对土壤综合肥力进行评价，以针叶豌豆根茬还田配施80%常规量氮肥处理提升土壤肥力的效果最为显著，土壤综合肥力指数较常规施氮肥处理提升23.0%。偏最小二乘法路径模型和聚合增强树分析表明，施肥处理主要通过调节土壤氮贮量影响玉米产量，土壤全氮、无机氮对产量的贡献率较高，分别为36.5%、26.8%。  【结论】  绿肥根茬连续还田条件下，减少后茬玉米氮肥常规用量的20%可维持甚至提高玉米产量，大幅提升玉米的氮磷钾吸收量和氮肥表观利用率。根茬还田配合适量氮肥可以通过提升土壤氮库贮量提高土壤综合肥力。在河西走廊，玉米产量和环境效益俱佳的栽培管理方式是针叶豌豆根茬还田配合80%的常规氮肥用量，毛叶苕子根茬还田配合80%～90%的常规氮肥用量。

Effects of returning the root of green manure on reducing N application in maize within their intercropping system in Hexi oasis irrigation area

  【Objectives】  Maize yield and soil fertility were investigated under the continuous return of green manure (GM) roots to the field and reducing fertilizer input in subsequent maize cultivation in a maize-green manure rotation system. We aimed to provide the basis for nutrient management to achieve sustainable and efficient crop production in the Hexi oasis irrigation area.  【Methods】  The long-term experiment was established in Hexi oasis, Gansu Province, in 2011. The two intercropping systems tested were needle leaf pea and hairy vetch with maize. The aboveground parts of the GM crop were cut as forage while the root remained in the soil. The sowing rows of GM and maize were exchanged every other year. Eight fertilizer treatments in maize were set up as no fertilizer application nor GM root control (CK), conventional N fertilizer rate (N 375 kg/hm2) without GM root retained (CF), retained GM root and applying N fertilizer at 0, 90%, and 80% of the conventional N fertilizer rate. At maize harvest in 2020, we analyzed the yield and NPK accumulation in maize straw and grain. Also, we collected 0–20 cm soil samples to determine the organic matter and N storage.  【Results】  Compared with CF, returning GM roots to the soil only (P<0.05) decreased maize yield. The combination of GM root and 80%, 90% conventional fertilizer application rate resulted in a similar or increased maize yield. It also increased the grain N, P, and K accumulation by 31.7%–56.4%, 37.8%–60.0%, and 61.7%–96.8%, respectively. Consequently, the agronomic efficiency of N fertilizer and apparent utilization by maize increased. The improved Nemoro Index Method showed that needle leaf pea with 80% N fertilizer application consistently enhanced comprehensive soil fertility, increasing by 23.0% compared with CF. Partial least squares regression and aggregated boosted trees analyses showed that fertilization treatments changed maize yield by regulating the soil N storage. The total and inorganic N concentrations had the highest contribution, accounting for 36.5% and 26.8% of the yield increase, respectively.   【Conclusions】  Retaining green manure roots continuously on the field could replace 10%–20% of N fertilizer input for subsequent maize. This practice stabilizes the maize yield, increases NPK content, and improves N fertilization efficiency. The practice improves comprehensive soil fertility by increasing N storage. We recommend that when GM roots are retained in soil, 80% of the conventional N fertilization rate should be applied in maize after needle leaf pea and 80%–90% after hairy vetch.