Nitrogen Transformations in Paddy Fields Applied with High Load Liquid Cattle Waste

概要

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Three varieties of forage rice (Oryza sativa L. cv. Hamasari, cv. Kusahonami, or cv. Leafstar) were transplanted respectively in plots established in a paddy field. Each of these varieties of rice was then subjected either to a basal treatment alone (control plots), or to a basal treatment plus subsequent treatment with liquid cattle waste (treatment plots). Nitrogen transformations differed significantly between the control plots and the treatment plots. The nitrogen uptake of the plants in the treatment plots was significantly higher than that of the control plants, even though there was no significant increase in biomass production observed. A mass transfer model calculation revealed that ammonia volatilization also increased following slurry application due to the high ammonium concentration and pH of the flood water. However, the total percentages of nitrogen loss through nitrous oxide, ammonia emission, and leaching loss in the treatment plots were only approximately 7-8%, which was significantly lower than the portion assimilated by rice plant. Moreover, nitrogen removal through denitrification was considered to be a major pathway for treatment plots, which probably accounted for most of the Unknown portion in nitrogen balance.