不同管理措施对黄土塬区农田土壤水分调控和硝态氮淋溶累积的影响

【目的】研究黄土区旱作农田不同施肥和覆盖处理对土壤水分与硝态氮淋溶的影响，以提高水肥利用效率，增加作物产量，为选取适宜于该区可持续生产的农田管理措施提供理论基础。【方法】选取渭北旱塬定位试验中不施肥对照、施氮磷化肥、氮磷化肥配施钾肥、氮磷化肥配施生物炭、氮磷化肥与休闲期地膜全覆盖、氮磷化肥与生育期地膜全覆盖和氮磷化肥与全年地膜全覆盖共7个处理。分析了不同处理连续耕作冬小麦15年后收获期剖面硝态氮累积和生长季内土壤剖面水分变化状况。【结果】与对照相比，施氮磷化肥处理显著增加了硝态氮在0—300 cm土层中的累积，累积量是对照的6.1倍。与施氮磷化肥相比，在氮磷化肥基础上生育期地膜全覆盖、配施生物炭、配施钾肥和全年地膜全覆盖处理显著减少了土壤硝态氮累积量，分别减少了78.7%、73.2%、66.0%和59.7%，氮磷化肥与休闲期地膜全覆盖土壤硝态氮含量较施氮磷化肥处理虽无显著差异，但硝态氮累积量也减少19.2%。与对照相比，施氮磷化肥处理对0—300 cm土层水分补给和消耗量无显著影响。与施氮磷化肥相比，氮磷化肥基础上配施钾肥和生物炭对土壤水分补给和消耗量也无显著影响，而施氮磷化肥基础上的休闲期地膜全覆盖、生育期地膜全覆盖和全年地膜全覆盖显著增加土壤水分补给量，其中只有氮磷化肥与休闲期地膜全覆盖处理显著增加了土壤水分消耗量。硝态氮在土壤中的累积受土壤水分运移影响，其在土壤中的累积量随着水分补给量的增加而增加。土壤水分运移能显著影响硝态氮在土壤剖面的分布，其结果是氮磷化肥与生育期地膜全覆盖和氮磷化肥配施生物炭处理硝态氮主要分布在0—20 cm土层，氮磷化肥配施钾肥和氮磷化肥与全年地膜全覆盖处理硝态氮主要分布在0—100 cm土层，而施氮磷化肥和氮磷化肥与休闲期地膜全覆盖处理硝态氮主要分布在0—200 cm土层，其中施氮磷化肥和氮磷化肥基础上配施钾肥、全年地膜全覆盖、休闲期地膜全覆盖4个处理出现硝态氮累积峰。【结论】不同农田管理措施通过对水分的调控减少硝态氮淋溶，进而提高氮素利用效率，其中在施氮磷化肥的基础上增加生育期地膜全覆盖能有效调控土壤水分运移和减少硝态氮淋溶累积，是旱塬区改善农田水肥状况，增加作物产量的适宜措施。

Effect of different agricultural measures on soil water and NO3–-N leaching and accumulation in cropland of the Loess Plateau

【Objectives】Fertilization and plastic film mulching affect soil water and fertilizer use efficiencies, the NO₃–-N leaching as well as winter wheat yields. This study compared the effects of different measurements to provide support to pursue suitable measures for sustainable development in the Loess Plateau.【Methods】A winter wheat field experiment was conducted in the dryland in Weibei since 2002. Seven treatments were tested, i.e., no fertilization control (CK), N and P fertilization (NP), NPK fertilization (NPK), NP plus biochar (NPB), NP and full plastic film mulching in summer fallow period (NPFFT), NP and full plastic film mulching in growth period (NPFGT), and NP and full plastic-film mulching in a whole year (NPFWT). Plowing after harvests and before winter wheat sowing was performed in all seven treatments. Accumulation of soil NO₃–-N at the winter wheat harvest stage for 15 years and soil water contents in the growing season were investigated.【Results】Compared with the CK, the NP significantly increased the accumulation of NO₃–-N in 0–300 cm soil layers, which was 6.1 folds of the CK. Compared with the NP, the NPFGT, NPB, NPK and NPFWT significantly reduced soil NO₃–-N accumulation by 78.7%, 73.2%, 66.0% and 59.7%, respectively. Although the soil NO₃–-N accumulation of the NPFFT was not significantly different from that of NP, it also decreased by 19.2%. Compared with the CK, the NP had no significant effect on water recharge and depletion in 0–300 cm soil layers. Compared with the NP, the NPK and NPB had also no significant effect on water recharge and depletion in 0–300 cm soil layers, while the NPFFT, NPFGT and NPFWT significantly increased soil water recharge, of which the only NPFFT significantly increased soil water depletion. Nitrate accumulation in soil was affected by soil water movement, and its accumulation in soil increased with the increase of water recharge. Soil water movement significantly affected the distribution of NO₃–-N in soil profile. The effect was that the NPFGT and NPB were mainly distributed in 0–20 cm soil layer, the NPK and NPFWT were mainly distributed in 0–100 cm soil layers, while the NP and NPFFT mainly distributed in 0–200 cm soil layer, of which the NPK, NPFWT, NPFFT and NP exhibited nitrate-nitrogen accumulation peaks.【Conclusions】Different agricultural cultivation measures could reduce the leaching of NO₃–-N by controlling soil water content, and thus improve the nitrogen utilization efficiency. The NPFGT effectively reduced the leaching and accumulation of NO₃–-N and regulated soil water movement, which was an appropriate measure for improving the condition of soil water and fertilizer, and increasing winter wheat yields in the dryland.