Seasonal and vertical changes in denitrification activity and denitrifying bacterial populations in surface and subsurface upland soils with slurry application

Abstract

The seasonal and vertical changes in the denitrification activity and denitrifying bacterial populations were investigated in surface (approximately 1 m depth) and subsurface (surface to 4 m depth) soils with slurry application where the nitrogen balance had been determined (Niimi and Nishida: 10th Nitrogen Workshop Programme and s, Vol. 4, p. 41, 1999). Slurry application generally enhanced denitrification in the surface soil, although the enhancement was not confirmed in the subsurface soil. Denitrifying bacteria in the surface soil also showed a potential denitrification activity, while, those in the subsurface soil were not related to the potential denitrification activity. Nitrogen loss by denitrification, which was estimated in the subsurface soil, ranged from O.1±O.2 to 58.5±81.0 kg-N ha-1 y-1, while, the loss from the surface soil ranged from 137.4±73.7 to 1,079.1±399.1 kg·N ha-1 y-1. The above results indicate that denitrification in the subsurface soil did not contribute to the reduction of nitrate-N leaching to the groundwater in fields with excessive application of slurry. Soil conditions required to depress the denitrification activity in the subsurface soil were examined.