南方稻作区水位调控对稻田氮素运移的影响与机制研究

Water level control is the key technique to realize the united regulation of irrigation-drainage in paddy field, which plays an important role in improving the ecological environment of paddy field. As the existing research is insufficient to show the rules of paddy nitrogen loss influenced by water level regulation, by taking paddy field of southern rice area as the research object and field water level control as the research carrier, the detail research on the key scientific problems of nitrogen migration and transformation mechanism, as well as water level regulation strategy, will be carried out by plot tests, laboratory physical and chemical analysis, model simulation and further field verification tests.. The research will clarify the migration law of nitrogen element respectively in the "paddy filed-drainage ditch" water environment and soil environment of paddy field profile, and reveal the variation of nitrogen in response to different water level control. In addition, relative soil, crop and meteorological factors of paddy fields under water level control will be monitored. The effect of relative soil, crop and meteorological factors under water level control will be quantitative analyzed. Based on the quantitative analysis above, the main influence factors of nitrogen element changes on different water level control will be determined and discussed. Considering three scenarios of the normal irrigation-drainage ditch without rainfall, drainage ditch with rainfall level backwater, and drainage ditch with rainfall, migration and transformation model of nitrogen in farmland scale will be constructed based on multiple factors. Moreover, the new migration and transformation model of nitrogen will be used to evaluate the nitrogen loss for various farmland water level schemes, and the high efficiency water level regulation mechanism of irrigation-drainage will be established. . The research results will have important theoretical meaning and application value. It will be helpful for establishing the evaluation system of water level regulation in paddy field of southern rice area, reducing nitrogen losses from paddy field, increasing the utilization rate of nitrogen fertilizer, and controlling agricultural non-point source pollution.

水位调控是实现稻田灌排联合调控的关键技术，在改善稻田生态环境方面发挥重要作用。针对水位调控对稻田氮素流失影响研究不足的问题，本项目拟以南方稻田作为研究对象，以水位调控作为研究载体，通过小区试验、理化分析、模型模拟、大田验证对稻田氮素运移规律、机理及调控机制等关键科学问题展开研究。. 通过研究阐明稻田“格田-排水沟”水体、剖面土层氮素运移规律，揭示稻田氮素变化特征对不同水位调控的响应规律，量化土壤、作物及气象参数对稻田氮素变化的影响，确定稻田氮素变化的主控因子；考虑水稻正常灌溉、降雨农沟水位有顶托、降雨农沟排水畅通三种情景，构建基于多因素的水位调控下稻田氮素运移转化模拟模型；应用模型对不同农田水位方案氮素流失进行评价，建立田间高效灌排水位调控机制。. 研究成果对构建南方稻作区水位调控评价体系，提高降雨及灌溉水利用效率，减少稻田氮素损失及控制农田面源污染具有重要的理论意义和应用价值。

本研究在节水灌溉-控制排水技术的基础上，采用田间试验、室内分析和模型模拟相结合的研究手段，研究了水位调控下，稻田水环境及根系土壤微环境氮素变化规律；研究了氮素变化的影响因子，包括土壤水分指标、土壤通气性指标、土壤温度指标等，进一步揭示稻田氮素迁移转化机。.1. 淹水10d，稻田田面水NH4+-N浓度降低7.3-71.4%，地下水NH4+-N浓度降低9.6-68.6%；稻田田面水NO3--N浓度降低32.5-74.5%，地下水NO3--N浓度降低2.9-51.8%。.2. 受旱对NH4+-N浓度影响较小；除分蘖期，NO3--N浓度都受旱-300mm大于受旱-600mm，分蘖期和拔节孕穗期地下水NO3--N浓度都处于较高水平。.3. 淹水条件下0-10cm、10-20cm土层土壤速效氮含量均呈现降低趋势。受旱可以明显提高各层土壤速效氮含量。.4. 受旱可以降低土壤含水率，控水水位变化对土壤含水量影响较大，控水历时对土壤含水量的影响不明显；稻田淹水恶化土壤通气状况，使氧化还原电位Eh降低。.5. 淹水使土壤的积温升高，降低土壤日变幅降，并且使最高气温出现时刻延迟；受旱处理表层土壤日平均温度略有降低，最低、最高土壤温度出现时刻均提前，日最高土温与土温日变幅均升高。.6. 利用氮素迁移模型对暴雨后常规灌排模式与水位调控模式稻田排水量及其NO3--N3和NH4+-N浓度进行模拟，模拟值与观测值拟合较好。.7. 利用熵权TOPSIS多目标决策模型分别对8个淹水方案和12各受旱方案的各生育阶段水位调控方案进行了综合排序，以此为依据，确定了水位调控机制。.8. 、与常规排水模式相比，水位调控模式水稻产量出现了轻微的减产，排水量和排水次数明显减少，NH4+-N、NO3--N损失量降低幅度分别为66.72%、55.56%，YUEIR、YUEWU和YUEET分别是常规排水模式水分利用效率的3.42、1.72和1.74倍。