Elucidation of Nitrogen Discharge Mechanism into Farming Soil System : A Step towards the Resource Circulation and Aqua-environmental Conservation in Watershed

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It searched for the strategy which controlled the amount of the exhaust NO_3-N load from one unit of farmland by paying attention as a biological denitrification, and trying the elucidation of the nitrogen outflow mechanism.It investigates in the alluvial fan where the feature is reproduced easily to clarify the presence of the denitrification with underground water under farmland, and the realities of the water quality change of underground water in the land use system from the field to the paddy field is understood. It was clarified that the principal cause of NO_3-N removal with underground water into undersoil layers of the paddy fields in the non-irrigated winter season was a biological denitrification.It paid attention to the generalizing paddy field which had a new farmland structure as a multi-purpose paddy field where it met idea and the requirement when the biological denitrification action during the surroundings year was able to appear by artificially creating the reduction layer, and it experimented on the lysimeter examination. As a result, NO_3-N decrease rate became 92%, NO_3-N removal in underground water was admitted by a high numerical value, and the utility became clear. In which were the principal causes of the decrease, the subordination nourishment microorganism which used the dominator in the soil system and the fortune-telling decomposition organism, it was possible to hold, and the possibility that autotrophic microorganisms which used the sulfur oxidation bacillus and CO_2 greatly took part was suggested. In addition, the cultivation examination which aims at amount to which the thing of the multi manure consolidating type plowing a field is steady is done, and it does continuing the water quality measurement. The stability of the quality and the amount of farm products clearly showed the nitrogen removal as a numerical value under the guaranteed condition.