Studies on the Control of Fate of Water, Heat, and Nitrogen in Agricultural Soils

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It is important to clarify the fate and the control of water, heat, and nitrogen in agricultural soils in the sense of environmental issues. We modeled the fete of water, heat, and nitrogen including mineralization, nitrification, and denitrification in soils and showed the possibilities to control the nitrogen movement and transformation by the artificial control of nitrogen and water applications and soil temperature. Specific knowledge is as follows;(1) Properties of nitrification process that produces nitrate in soils were become clear using two typical Japanese upland soils (sand and andosol). The rate of nitrification of andosol was much larger than one of sand. Nitrification of andosol highly depended on soil moisture and soil temperature.(2) The amount and timing of nitrogen applications effected on soil profiles of various cations and anions during infiltration process in the case of sand. Modeling technique of nitrogen and water fates in soil including nitrification could represent the results of infiltration experiments for sand and andosol.(3) Long-term water and nitrogen transfer simulations showed that split fertilizer and water applications could reduce the risk of nitrogen leaching into groundwater. Increase of soil temperature under green house cultivation would activate nitrification and give rise to the risk of nitrogen leaching.(4) Fate of liquid dairy manure nitrogen in an irrigated double crop corn-grain rotation in California could be modeled numerically including mineralization, nitrification, and denitrification.(5) In terrace paddy fields, temporal changes in groundwater level were much larger at the part of upper side of the slope than at the part of under side of the slope. Soils at under side of the slope were always under deoxidized condition and hydrogeochemical and molecular biological approaches showed that the existence of the slope was important to reduce the nitrate discharge to downstream by denitrification.