Relationship between the amount of organic material applied and soil biomass content

Abstract

The relationship between the amount of organic material applied and soil biomass content was examined in soils amended with various organic materials in 4 upland experimental fields. The values of the soil biomass measured by the direct microscopic method (DMM), ATP content, and soil respiration rate in the soil amended with organic material were greater than those in the soil amended with inorganic fertilizer in all the fields. Soil biomass measured by the DMM and ATP content were highly correlated with the sum of the amount of hot water-soluble organic substance, carbohydrate, and crude protein components in the organic material applied in all the fields. Soil respiration rate was also highly correlated with the sum of the amount of these components applied in the 3 fields. These results suggest that hot water-soluble organic substance, carbohydrate, and crude protein components in organic material are closely related to the increase of the soil biomass. The difference in the soil biomass C content calculated from the ATP content among the 4 fields generally paralleled the difference in the soil total C content. The ratio of biomass C to the total C in the field with a high total C content was lower than that in the field with a low total C content. The rates of increase of the soil biomass measured by the DMM, ATP content, and soil respiration rate in the field with short-term application of organic material were higher than those in the field with long-term application. These findings suggest that the rate of increase of the soil biomass is high when the duration of application of organic material is short.