Nitrogen Budget and Ammonia Volatilization in Paddy Fields Fertilized With Liquid Cattle Waste

A study was conducted to determine nitrogen budget and ammonia volatilization in Japanese paddy fields supplemented with liquid cattle waste (LCW). A series of four, 2 × 10 m experimental plots was established in a paddy field with silty clay soil planted with forage rice (Oryza sativa L.). In addition to 195 kg N ha−1 of chemical or compost-based basal fertilizer, LCW was applied as an additional fertilizer at total nitrogen rates of 0, 255, 255, and 405 kg N ha−1 to the four plots C195, T450-1, T450-2, and T600, respectively. The mass balance showed that after application of LCW, 32–39% of total input nitrogen was assimilated into aboveground parts of rice plants, 11–15% leached downward, 2.5–4.0% was lost via ammonia volatilization, 1.6–5.1% was retained in roots or was adsorbed onto soil, and approximately 30–40% was lost via denitrification. Compared to animal waste slurries applied to unsaturated soils, nitrogen loss via ammonia volatilization was relatively lower, probably due to the dilution effect of floodwater. Nitrogen loss via denitrification was markedly higher in areas where LCW was applied compared to areas without LCW application. On the other hand, nitrogen leaching downwards represented a substantial loss and may be an environmental concern. However, after LCW application only, the ammonium ion was detected, at a maximum nitrogen concentration of 11.4 mg L−1. In this system, therefore, nitrogen has a different fate to that in animal waste slurries applied to unsaturated soil. In that situation, the major nitrogen form in leaching water is nitrate nitrogen, which moves readily into groundwater.