Abstract
Denitrification rates in 4 different kinds of soils applied with organic materials were determined together with CO_2 emission rates by the combination of an acetylene inhibition method and an intact core method. The soil types examined were Cumulic Andosols, Low-humic Andosols, Yellow soils, and Gray Lowland soils. The applied organic materials were cattle feces compost and dried hog feces. The application rates of the organic materials were adjusted so that the practical amounts of N supply for the crops were equivalent to chemical fertilizer. The significant results obtained in this study are described below. 1) The denitrification rates were remarkably enhanced by the application of dried hog feces. The rates after 3 days from the application ranged from 0.2-0.5mg N kg^<-1> d^<-1>, and were especially high in Yellow soils and Gray Lowland soils. The results indicated that the significant period for calculating the total amount of denitrification was within 1 month after the application of organic materials. 2) Effect of irrigation on denitrification was experimentally investigated by adding water to the soil cores after 3 days from the application of organic materials. Although the irrigation positively affected both CO_2 emission and denitrification, only denitrification was enhanced by two or three orders of magnitude in the soils amended with dried hog feces. 3) The square roots of denitrification rates were highly correlated with CO_2 emission rates. This suggested that denitrification rates were probably dependent on the amount of denitrifying enzyme in the soil and the development of anoxic conditions, both of which were affected by the decomposition of applied organic materials.
