不同水肥措施下华北露地菜地氮淋溶特征

华北地区典型一年两季露地蔬菜种植系统,蔬菜生长季水热同季、种植管理中水氮供应充足且往往过量,造成大量氮素淋溶到深层土壤,不仅造成水肥资源利用率低,对地下水质也造成威胁。本文以华北潮褐土黄瓜-白菜一年两季典型露地蔬菜为研究对象,利用田间试验研究不同氮肥用量及优化措施(包括抑制剂、生物炭、秸秆还田)以及控制灌溉量对蔬菜产量、土壤氮淋溶及氮平衡的影响。研究结果表明:1)华北典型露地菜地氮肥主要损失去向为深层土壤中积累及氮淋溶。2)农民常规施肥处理黄瓜季和白菜季各施550 kg(N)·hm~(-2)]淋洗出80cm土壤剖面的总氮占当季氮肥施用量的10.0%,减氮20%和50%分别使总氮淋溶量降低23.8%和45.6%;减氮20%对蔬菜产量没有显著影响,减氮50%对水肥需求量较高的黄瓜产量有显著影响(减产19.6%)。3)减氮20%配合脲酶抑制剂和硝化抑制剂、施用生物炭和添加秸秆还田分别使全年总氮淋溶量比常规水肥处理降低40.7%、43.0%和34.3%,而对蔬菜产量没有显著影响。4)减少灌溉量15%和30%分别使总氮淋溶比常规水肥处理降低43.1%和50.5%,水氮协同调控对降低氮淋溶效果显著;对需水量较高的黄瓜季,灌溉量降低30%黄瓜产量显著降低13.9%。5)高量水肥投入条件下连续种植蔬菜3年6季后,0～80cm土壤剖面硝态氮积累量占0～200 cm土壤剖面积累量的38.2%～50.7%,土壤剖面积累了大量硝态氮而且向深层土壤中移动。因此,合理控制水肥管理,特别是减氮结合脲酶抑制剂和硝化抑制剂配合水分管理,是经济可行的有效阻控土壤氮淋溶的措施。

The effects of water and fertilizer practices on nitrogen leaching in open-field vegetable soil in North China

Groundwater nitrate pollution is a concern for the government and scientific community. During the growth period of open-field vegetables in North China, water and nitrogen (N) are often excessively used, resulting in a lower efficiency rate, which threatens groundwater quality. A field experiment was conducted in cinnamon soil on cucumber and Chinese cabbage crop rotation farmland to evaluate the effects of water and fertilizer on crop yields, N leaching, and N balance. Four standard N treatments were used conventional N application in each vegetable season, 550 kg(N)·hm^-2·a^-1, N3; 20% less N, N2; 50% less N, N1; no nitrogen, CK], and leaching was monitored using a lysimeter. Five additional treatments were tested that combined a 20% N reduction with an alternative management practice: urease and nitrification inhibitors (N2I), biochar (N2B), straw incorporation (N2S), 15% irrigation reduction (N2W1), and 30% irrigation reduction (N2W2). The results showed that deep soil nitrate accumulation and root zone nitrogen leaching were primarily nitrogen loss. Using conventional N (N3), 10.0% of the applied N leached from the 80 cm soil layer, and the leached amount decreased by 23.8% and 45.6% by using 20% less N (N2) and 50% less N (N1), respectively, compared with that of N3. A 20% N reduction did not affect vegetable yield, but a 50% reduction decreased the cucumber yield by 19.6%. The combined practices (inhibitors, biochar, and straw) decreased the total leached N by 40.7% (N2I), 43.0% (N2B), and 34.3% (N2S) without affecting yields. Reducing irrigation decreased the total leached N by 43.1% (N2W1) and 50.5% (N2W2) compared with N3, but N2W2 decreased the cucumber yield by 13.9%. After three years (six continuous seasons), large amounts of nitrate accumulated and then moved to deeper soil. Nitrate accumulation in the 0-80 cm soil layer after conventional fertilization accounted for 38.2%-50.7% of the 0-200 cm soil layer, which was high compared to other management practices. Decreasing water and N fertilizer use combined with urease and nitrification inhibitors may reduce N leaching and cost. These results provide solutions for improving water and nitrogen management, thereby decreasing soil nitrate accumulation and deep soil leaching, reducing vegetable production and groundwater quality threats.