摘要:为阐明黑土春玉米田氮素的淋溶风险与阻控机制，运用田间原位15N示踪技术，设常规垄作、免耕无秸秆覆盖和免耕100%秸秆覆盖（秸秆量为7500 kg·hm-2）3个处理，量化了长期免耕秸秆覆盖措施下氮素在不同形态氮库中的转化特征、淋溶运移规律和去向。结果表明：农民常规施肥量条件下，常规垄作、免耕无秸秆覆盖和免耕全量秸秆覆盖均已导致东北黑土春玉米田0~300 cm土壤剖面中分别累积461.6 kg（N）·hm-2、450.7 kg（N）·hm-2和439.7 kg（N）·hm-2的矿质氮，且主要是硝态氮（占比分别为84.2%、79.5%和81.7%），存在着氮素的淋溶损失风险。当季施入肥料氮对玉米苗期和抽雄期0~40 cm土层总硝态氮库累积的贡献率平均为60.9%和58.0%，其淋溶损失风险较高。与常规垄作处理相比，免耕全量秸秆覆盖降低了0~40 cm土层肥料氮向矿质氮库的转化，降低比例达20.8%；增加了其向黏土矿物固定态铵和有机氮库的转化，提高比例分别为39.4%和30.5%。0~20 cm土层，黏土矿物对肥料来源铵的固定能力和微生物对肥料来源矿质氮的固持能力基本相当；20~40 cm土层，固持能力前者高于后者，说明外源碳输入的数量及其与土壤微生物的接触程度共同决定着对矿质氮的固持潜能。通过免耕和秸秆覆盖调控机制，可阻控黑土春玉米田矿质氮在土壤剖面的大量积累，使氮肥利用效率和玉米产量均提高9.7%，氮肥的气态损失降低27.7%，延缓肥料氮向深层土壤剖面淋溶运移的速率。
关键词:免耕/
秸秆覆盖/
15N示踪/
迁移转化/
淋溶损失
Abstract:Nitrogen (N) availability and retention in soil-crop systems are important for increasing crop productivity, improving N use efficiency (NUE), and minimizing environmental pollution from N losses. In the black soil region of Northeast China, it is unclear how agricultural management practices affect soil mineral N accumulation and leaching. In this study, an in-situ 15N-labeled tracer field experiment was performed to quantify the transformation characteristics, migration, and soil N fate when long-term no-till with maize stover mulching was used. The soil profile was investigated under three treatments: conventional ridge tillage (RT), no-till with no maize stover mulching (NT0), and no-till with 100% maize stover mulching (NT100; 7500 kg·hm-2 maize stover). The accumulated mineral N [primarily as nitrate nitrogen (NO3--N)] in the 300 cm soil profiles were 461.6 kg(N)·hm-2 (RT), 450.7 kg(N)·hm-2 (NT0), and 439.7 kg(N)·hm-2 (NT100) when traditional fertilizer applications were used, suggesting a N leaching risk. In all 0–40 cm soil layers, the percentage of fertilizer-derived NO3--N to total NO3--N was on average 60.9% (maize seedling stage) and 58.0% (maize tasseling stage), indicating a high N leaching risk in the seasonally applied fertilizer. NT100 decreased the transformation of fertilizer N into mineral N pools by 20.8% in 0–40 cm soil layers but accelerated the conversion into fixed ammonium NO3--N and organic N pools by 39.4% and 30.5%, respectively, compared with that by RT. The clay mineral to fertilizer-derived NO3--N fixation capacity was the same as the soil microorganism to fertilizer-derived mineral N immobilization capability at a depth of 0–20 cm, but the fixation capacity was higher than the immobilization capability at 20–40 cm. These findings suggest that the immobilization potential of soil microorganism to fertilizer-derived mineral N is dependent on the maize straw mulch quantity and maize straw accessibility to soil microorganisms. No-till with maize stover mulching reduced the soil mineral N accumulation in black soil spring maize fields, increased the fertilizer nitrogen use efficiency and maize yield by 9.7%, decreased the fertilizer N gaseous loss by 27.7%, and delayed fertilizer N leaching to deeper soil.
Key words:No-tillage/
Stover mulching/
15N-labeling/
Migration and transformation/
Leaching loss
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