设施栽培下作物根区及深层土壤氮素转化迁移规律及模拟

Protected agriculture has been developed greatly in the last 30 years in china, which in turn increase the farm's income and improve peoples' life. However in another side, greater water and nitrogen use in this system imposes much nitrogen left in soil layer, which will or did polluted ground water system. Therefore, knowing the changes of soil physical, chemical and biological properties and the related process of nitrogen cycle and moving is the base for determining the proper amount of irrigation and fertilizer, and for making proper policy of protecting groundwater. Hence in this study, we will conduct a field-laboratory combined experiment by using the isotope and numerical model methods to (1) study the dynamic patters of soil nitrogen and nitrogen balance in root zone and quantify the nitrogen flux at the both up and blow surfaces of the root zone, (2) analyze the nitrogen transformation and moving processes and related soil physical, chemical and biological properties in the deep soil layer (>3m), (3) study the changes of soil properties and the nitrogen flux in the interface of soil and groundwater. Based on the above results, a combined model will be developed to model the nitrogen cycle and moving in the soil layer from soil surface to the groundwater level. Then this model will be used to compare nitrogen balance under different nitrogen and water application conditions. Based on these modeling results, we will determine proper application amounts of nitrogen and irrigation water for sustainable development of protected agriculture in China.

我国设施农业在过去30年中取得了长足发展，显著增加了农民收入和改善了人民生活条件。但是其高强度的水肥施用，使得土壤中残留了大量氮素，这不仅显著改变了土壤理化及微生物环境，也加剧了污染地下水体的风险，而研究清楚设施种植区土壤理化性质变化条件下的氮素转化和循环机理及氮素在深层土壤中迁移规律，则是确定合适灌溉施肥量及制定农业面源污染控制措施的基础。因此，本研究通过大田和室内试验，采用同位素示踪和数值模拟结合的研究方法,分析设施农业条件下根区土壤氮素动态过程和氮平衡，确定根区上下界面氮通量及主要影响要素；研究深层土壤（>3m）的理化和生物性质变化及与设施农业种植要素的关系，明晰深层土壤内氮素的转化过程和运动规律；探究土壤与地下水交界处土壤理化性质及氮通量的变化；基于以上成果建立设施农业条件下考虑地表至地下水面以上土壤层内氮素转化和迁移的数学模型并率定相关参数，通过情景分析提出适宜的施肥量和灌溉量。

项目通过4年的日光温室试验，利用同位素示踪、试验取样分析和模型模拟，研究了氮素在土壤中的分布和运移规律，以及典型蔬菜（黄瓜）对不同施氮量的响应规律，评价了不同施氮量条件下作物的水肥利用效率。结果显示，在滴灌条件下，土壤中的氮素主要分布在0~50cm的土层内，这也是作物的主要根系分布区；但是定植后大水灌溉可使得氮素运移到1m以下，深层土壤中的氮素通过4年试验已经运移到8m以下，年向下运移速率到达2m；经过4年试验土壤表层的pH值下降了1，表明土壤有明显的酸化趋势。施氮量为当地施肥量的100%，75%和50%时，产量有一定的降低，但是下降幅度不显著。与当地常规的畦灌相比，在总体产量差异不明显的情况下，滴灌条件下平均灌溉水量却减少了422mm/季节，约42.7%，水分生产率提高了75.9%；滴灌处理的氮素表观利用率分别提高了0.1%~62.5%，农学效率提高了3.5~258.1kg（黄瓜）/kg(N)；经济效益显示，滴灌处理在4个生长季节的收益平均增加了2.66~10.89万元/ha，但是施肥为50%施肥量的滴灌处理收益年纪变化较大。综合考虑产量、价格和氮素利用效率，推荐滴灌施肥量为当地施肥量的75%，灌溉时间以20cm深度处水势为-10kPa为宜。项目得到氮素的深层运移速率为2m/年，表明在目前种植模式下土壤酸化趋势明显，且已经有大量的氮素渗漏到根系层以下，对地下水污染造成了潜在的危险。同时消减施肥量25%不会对经济效益造成显著影响。研究成果对于指导设施蔬菜施肥，提高水肥利用效率和保护土壤及地下水环境提供了理论和数据支撑。