节水灌溉稻田水氮迁移转化机理及模拟

发布时间：2018-09-06 18:09

【摘要】：水稻是中国主要的粮食作物之一,稻田种植面积约占粮食作物种植总面积的28%,其产量约占粮食作物总产量的40%。稻作区水资源短缺已成为当地农业生产中的重要问题。与传统淹灌稻田相比,干湿交替稻田面临的水氮迁移转化问题更为复杂,受土壤水分和温度变化的影响更为严重。节水和省肥(氮肥)这两个水稻生产中重要的目标在干湿交替稻田中可能互为一对矛盾体。如何让干湿交替灌溉达到此两目标最优,有赖于研究水氮在干湿交替水稻土壤中的迁移转化机理,确定合理的精确灌溉制度和氮肥施用措施。本文以稻田田间土壤-水稻-大气连续体系统为研究对象,采用野外田间水氮试验观测,室内土壤理化分析和田间一维水氮迁移转化模拟等三种手段,研究了水氮在干湿交替条件下的迁移转化规律,揭示了稻田水氮情势随灌溉和降水变化的内在机理,探求了干湿交替稻田节水、省肥和高产的水氮高效利用机制。本文主要研究内容和结论如下：(1)试验监测了干湿交替灌溉和长期淹灌稻田水渗漏和氮素渗漏量,比较研究了干湿交替灌溉的运用对水稻生长和作物产量的影响,以及干湿交替稻田与传统淹灌稻田水氮入渗的区别与联系。干湿交替节水灌溉在田间层面对产量没有不利的影响。施氮能显著增加粮食产量,但氮素生产率反而随着施氮量增加而下降。干湿交替灌溉的成功实施减少了灌溉水的投入,一是由于减少入渗和渗漏损失。但是,由于在干燥阶段形成的裂缝,干燥后再湿润时期的优先流造成大量的田间水渗漏流失。犁底层的土壤是防止渗漏的关键,所以干燥时期的裂缝和收缩不应该延伸至犁底层。干湿交替灌溉田块的地下水的毛细上升占水投入总量的26.1-27.4%。干湿交替灌溉在很大程度上减少了灌溉用水,二是由于其增加了地下水毛细上升。因此,在设计灌溉制度时应该考虑地下水毛细上升对节水灌溉的贡献。水稻生长季节干湿交替灌溉田块渗漏水硝态氮浓度比同时期长期淹灌田块高64%,干湿交替灌溉田块的硝态氮渗漏损失比长期淹灌田块增加了29.4%。故干湿交替灌溉能诱导更高的氮素损失,增加稻田氮素渗漏的风险。干湿交替灌溉稻田和长期淹灌稻田中氮素的来源和去向均有很大不同。相较于长期淹灌,干湿交替灌溉加强了氮素转化过程,包括硝化-反硝化,矿化和挥发作用等,从而增加了氮素的气态排放和潜在的温室气体(N2O和NH4)排放。水稻可持续生产中干湿交替灌溉的成功实施需要充分考虑此负面效应。(2)针对室内外长期水氮试验,构建土壤特征参数、田间水氮情势和气候微环境数据库,利用其进行了HYDRUS-1D和系统动力学模型模拟研究。系统动力学模型能够最大限度地简化田间水氮平衡分析,HYDRUS-1D模型能很好地处理干湿交替灌溉稻田和长期淹灌稻田中动态变化的边界条件。尽管HYDRUS-1D模型不能通过一阶动力反应链完全描述所有氮素转化过程,稻田各形态氮素浓度和平衡能够通过集合一些相似的氮素转化过程,利用HYDRUS-1D模型来分析和模拟。因为HYDRUS-1D模型能够处理氮素转化参数值对土壤含水量的变化,所以HYDRUS-1D模型能很好得被应用于比较干湿交替灌溉稻田和长期淹灌稻田中的水氮情势,评价稻田中水氮平衡各要素,为稻田水氮管理提供决策依据。(3)试验研究了南方水稻灌区塘堰系统水肥重复利用对区域节水和减少农业面源污染的作用。研究表明,在水稻生长季节,灌溉塘堰可以有效地提高农业排水再利用和减少污染物排放。降水是决定塘堰回归水再用率的决定性因素。充分利用塘堰的蓄水容积收集上游稻田回归水和调控塘堰出流最大限度用于下游灌溉同样可以提高塘堰回归水利用率。塘堰水质监测表明,灌溉塘堰去除农田排水中47.2%的总磷和60.8%的总氮,并对增加农业排水和灌区径流的泥沙沉降,其悬浮物去除率平均达到68.4%。铵态氮是稻田回归水中的主要氮素污染物,而颗粒态磷是回归水中的主要磷素污染物。颗粒态磷占灌溉塘堰入流总磷的90%。较长的水力停留时间有利于提高总氮负荷去除率,而磷负荷去除率与水力停留时间关系不确定。因此,整合灌溉塘堰对回归水和营养物的再利用,对减少农田氮和磷向区域外排放有重要意义,对稻田的生态环境改善具有积极意义。
[Abstract]:Rice is one of the main grain crops in China. The planting area of paddy field accounts for 28% of the total planting area and its yield accounts for 40% of the total grain yield. Water shortage in paddy field has become an important problem in local agricultural production. Water saving and fertilizer saving (nitrogen fertilizer) are two important objectives in rice production, which may be a pair of contradictions in alternate dry and wet paddy fields. In this paper, the soil-rice-atmosphere continuum system in paddy field was used as the research object to study the transfer and transformation of water and nitrogen under the condition of alternating wetting and drying by means of field water and nitrogen experimental observation, indoor soil physical and chemical analysis and field one-dimensional water and nitrogen transfer and transformation simulation. The main research contents and conclusions are as follows: (1) The water and nitrogen leakage and nitrogen leakage of paddy fields under alternate irrigation and long-term flooding irrigation were monitored and compared. The effect of alternate irrigation on rice growth and crop yield, and the difference and relationship between dry-wet alternate paddy field and traditional flooded paddy field were studied. Successful implementation of wet alternate irrigation reduces the input of irrigation water. First, it reduces the loss of infiltration and leakage. However, due to the cracks formed in the drying stage, preferential flow during the drying and wetting period results in a large amount of field water leakage and loss. The soil at the bottom of the plough is the key to prevent leakage, so the cracks and shrinkage during the drying period do not occur. The capillary rise of groundwater accounts for 26.1-27.4% of the total water input in dry-wet alternate irrigation fields. Dry-wet alternate irrigation greatly reduces irrigation water use and increases the capillary rise of groundwater. Therefore, the contribution of capillary rise of groundwater to water-saving irrigation should be considered in designing irrigation schemes. Nitrate nitrogen concentration in seepage water of paddy field under alternate dry-wet irrigation was 64% higher than that under long-term flooding irrigation during the growing season, and nitrate nitrogen loss in alternate dry-wet irrigation was 29.4% higher than that under long-term flooding irrigation. Compared with long-term flooding irrigation, dry-wet alternative irrigation enhances nitrogen transformation processes, including nitrification-denitrification, mineralization and volatilization, thus increasing nitrogen gaseous emissions and potential greenhouse gas emissions (N2O and NH4). Successful implementation of alternative irrigation requires full consideration of this negative effect. (2) For indoor and outdoor long-term water and nitrogen experiments, soil characteristic parameters, field water and nitrogen situation and climatic micro-environment database were constructed, and HYDRUS-1D and system dynamics model were used to simulate the field water and nitrogen balance. The HYDRUS-1D model can well deal with the boundary conditions of dynamic changes in paddy fields under alternate dry-wet irrigation and long-term flooding irrigation. Although the HYDRUS-1D model can not fully describe all nitrogen transformation processes through a first-order dynamic response chain, the concentration and balance of nitrogen forms in paddy fields can be combined by some similar nitrogen transformation processes, and the H-DRUS-1D model can be used to describe all nitrogen transformation processes in paddy fields. Because HYDRUS-1D model can deal with the change of soil water content caused by nitrogen transformation parameters, HYDRUS-1D model can be well applied to compare the water and nitrogen situation in paddy fields under dry-wet alternate irrigation and long-term flooding irrigation, to evaluate the water and nitrogen balance in paddy fields, and to provide a decision for paddy field water and nitrogen management. (3) The effect of water and fertilizer reuse on regional water saving and agricultural non-point source pollution reduction in the pond and weir system of southern rice irrigation area was studied experimentally. Fully utilizing the storage capacity of the pond weir to collect the returning water from the upstream paddy field and regulate the outflow of the pond weir for the downstream irrigation can also increase the utilization rate of the returning water from the pond weir. The average removal rate of suspended solids was 68.4%. Ammonium nitrogen was the main nitrogen pollutant in the returning water of paddy field, and particulate phosphorus was the main phosphorus pollutant in the returning water. Therefore, the reuse of returning water and nutrients by integrated irrigation ponds and weirs is of great significance to reduce nitrogen and phosphorus emission from farmland and to improve the ecological environment of paddy fields.
【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S511

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