Studies on Movement and Transformation of Inorganic Nitrogen in Porous Media

阐明了旱地和水田两种不同农田氮素循环的去向机制，以期提出通过人为控制水环境来管理氮素循环。(1)在日本，红壤和沙土都是典型的旱地土壤。由于红壤具有发达的孔结构，其硝化作用(产生硝酸盐的过程)相对高于沙丘沙地。制定了硝化过程和入渗条件下氨氮和硝态氮在两种土壤中的运移规律。(2)由于地下水硝酸盐污染问题一直很严重，因此在加州农田土壤中应用液态奶肥氮肥是一个重要的问题。有机氮、氨氮和硝态氮在灌溉玉米-籽粒轮作中的迁移转化可用数值模拟，包括矿化、硝化和反硝化作用。在梯田水田中，坡面土壤氧化还原环境的时空变化较为复杂。水文地球化学和分子生物学方法表明，坡度的存在对梯田氮素循环起着重要作用。(4)设计并搭建了反硝化生物反应器，考察了多孔介质中反硝化细菌对周围环境变化的适应性。生物反应器系统可用于水质控制系统中硝酸盐的净化。(5)采用聚合酶链式反应和变性梯度凝胶电泳法的分子生物学方法对于分析多孔介质中的细菌群是非常有用的。

We clarified mechanisms of fate of nitrogen cycling in two different agricultural lands that are upland field and paddy field in order to propose the management of nitrogen cycling by artificially controlling water environments.(1) In Japan, both andosol and sand are typical soils for upland field. Nitrification, the process of producing nitrate, in andosol was relatively higher than in dune sand because andosol had the developed pore structures. We formulated nitrification process and ammonia and nitrate movements under infiltration in two types of soil.(2) Liquid dairy manure nitrogen applied to field soil in California is important issue because nitrate contamination of groundwater has been very serious problem. Movement and transformation of organic-, ammonia-, and nitrate-nitrogen in an irrigated double crop corn-grain rotation could be modeled numerically including mineralization, nitrification, and denitrification. It would be helpful for decision of the management of manure and the optimal design of dairy farming.(3) In terrace paddy fields, spatial and temporal changes in redox environment in soil at the part of slopes were considerably complex. Hydrogeochemical and molecular biological approaches showed that the existence of the slope played important roles in nitrogen cycling in terrace paddy filed.(4) We designed and made up the bio-reactor of denitrification to examine activities of denitrifying bacteria in porous media that were flexible against the change in the surrounding environment. Bio-reactor system was available to clean-up of nitrate in water quality control system.(5) Molecular biological approaches using PCR (Polymerase Chain Reaction) and DGGE (Denatured Gradient Gel Electrophoresis) techniques are found to be very useful for analyzing consortia of bacteria in porous media.