Studies on Movement and Transformation of Inorganic Nitrogen in Porous Media

通过对旱田和水田两种不同农业用地氮素循环命运机制的研究，提出了人工控制水环境对氮素循环的管理。(1)在日本，土土和沙土都是典型的旱田土壤。由于土土孔隙结构发达，其产生硝酸盐的硝化作用相对高于沙丘砂。研究了两种土壤在入渗条件下的硝化过程和氨、硝态氮的运动规律。(2)由于地下水硝酸盐污染问题十分严重，因此在加州农田土壤中施用液态乳肥氮是一个重要问题。有机氮、氨氮和硝态氮在双季轮作灌溉条件下的运动和转化可以通过数值模拟来模拟，包括矿化、硝化和反硝化作用。研究结果对奶牛粪肥管理决策和奶牛养殖优化设计具有一定的参考价值。(3)阶地水田坡地部分土壤氧化还原环境时空变化较为复杂。水文地球化学和分子生物学研究表明，坡地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。采用生物反应器系统对水质控制系统中的硝酸盐进行了净化。(5)利用PCR（聚合酶链反应）和DGGE（变性梯度凝胶电泳）技术的分子生物学方法对分析多孔介质中的细菌群落非常有用。

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.