Nitrogen Transformations in Paddy Fields Treated with High Loads of Liquid Cattle Waste

摘要

Three varieties of forage rice (Oryza sativa L. cv. Hamasari, Kusahonami, and Leafstar) were transplanted in plots established in a paddy field. Each of these varieties of rice was then subjected either to basal treatment alone (control plots), or to basal treatment plus subsequent treatment with liquid cattle waste (treatment plots). The 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 in the control plants, even though no significant increase was observed in biomass production. A mass-transfer model calculation revealed that ammonia volatilization also increased following slurry application because of 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 the rice plant. Moreover, denitrification was considered to be a major pathway for nitrogen removal in the treatment plots; this probably accounted for most of the "Unknown" portion in the nitrogen balance.