旱地覆膜栽培土壤氮转化过程及其对土壤氮去向的作用机理

Plastic film mulching, as a cultivation for drought-resistant and moisture-conserving, has been largely accepted for maize production in rain-fed agricultural area. However, as the increasing of crop yields, the excessive fertilizer application is more and more serious in plastic film mulching system. It leads to low nitrogen use efficiency and high nitrate accumulation in soil, which may pose risk to environment and cause soil degradation. Soil nitrogen transformations play important role in regulating the nitrogen fate; however the nitrogen transformation processes and its regulation for nitrogen fate is not clear under plastic film mulching, due to the lack of quantitative research on nitrogen transformations in this system. Therefore, this study will focus on soil nitrogen transformations in plastic film mulching system, to 1) measure the gross nitrogen transformation rate, by a 15N tracing incubation experiment combined with the MCMC model which will be conducted both in laboratory and in situ, and a DENIS denitrification incubation system; 2) investigate the temporal dynamics of soil nitrogen transformations and their factors and microbial mechanisms; 3) measure nitrogen fate by an in situ monitoring study; and 4) clarify the mechanisms for nitrogen transformations regulate soil nitrogen fate in plastic film mulching system. We anticipate the study will be benefit for improving nitrogen use efficiency, controlling N loss and maintaining agriculture sustainability in plastic film mulching system of drylands.

覆膜栽培作为抗旱保墒增产的耕作措施，在旱作农业区得到广泛推广和应用。但该系统大量耗肥问题日益突出，导致氮肥利用率低，土壤硝酸盐大量累积，引起环境风险与土壤质量下降。土壤氮转化过程对氮去向具有至关重要的调控作用；但覆膜下土壤氮转化过程的定量研究较少，使得其转化特征及对氮去向的作用机制不够明确。本项目拟在对覆膜土壤水、热、碳及微生物连续监测的基础上，采用室内培养与原位培养的15N成对标记技术结合MCMC数值模型，以及DENIS直接测定N2法，测定作物生长不同阶段及休闲期覆膜下土壤氮素初级转化速率，明确其转化特征及影响因素与微生物机理；结合氮去向观测，研究氮去向的特征与数量大小，探讨土壤氮素初级转化速率与氮去向在时间与数量上的关联性，从氮转化过程的角度阐述覆膜栽培下土壤氮去向的机理。该研究对于提高旱地覆膜系统氮素利用率，减少氮素损失，维持旱作农业覆膜体系的可持续发展具有重要的理论与实践意义。

土壤氮转化过程对氮去向具有至关重要的调控作用，但覆膜下土壤氮转化过程特征及对氮去向的作用机制仍不明确。本项目以黄土高原旱地典型覆膜栽培方式（垄沟覆膜）玉米地为研究对象，运用大田实验结合室内培养试验的研究方法，采用15N成对标记技术结合MCMC数值模型，测定了作物生长不同阶段覆膜下土壤氮素初级转化速率，明确其转化特征及影响因素与微生物机理；同时结合氮去向观测，探明了土壤氮素初级转化速率与氮去向在时间与数量上的关联性，从氮转化过程的角度阐述了覆膜栽培下土壤氮去向的机理。研究结果表明，垄沟覆膜体系下土壤氮初级转化过程决定了土壤氮形态与大小，土壤氮转化特征以及植物和微生物对氮的需求调节了氮的去向和数量。与不覆膜相比，覆膜下土壤初级矿化速率低，但初级硝化速率与氮损失相对小，由此造成覆膜下氮净矿化量反而较高。覆膜有助于优化土壤营养环境，增强土壤环境稳定性，提高微生物对于环境的胁迫耐受性，并提高土壤各微生物类群活性；但覆膜对于氮转化酶活性的影响因酶种类而异。影响覆膜下土壤氮转化过程的非生物因子主要为土壤氮素状况和土壤温度，生物因子主要为土壤酶活性。覆膜减少了N2O、NH3等温室气体排放量，提高了土壤剖面硝酸盐积累量与作物氮吸收量，并增加了作物产量。研究表明，土壤氮转化过程调节了土壤氮素形态和数量，使其与覆膜体系下玉米生长所需的氮素水平相匹配，从而促进作物氮素吸收，提高作物产量，减少氮素损失。本研究从氮转化过程的角度阐述了覆膜栽培下土壤氮去向的机理，有助于为提高旱地覆膜系统氮素利用率，减少氮素损失，维持旱作农业覆膜体系的可持续发展提供科学指导依据。