Effects of N fertilizer treatments on biologically active N pools in soils under plow and no tillage

Studies assessing the effects of different tillage and N fertilizer management practices on distributions and amounts of various C and N pools in soil can provide information about the influence of such management on the quality of organic matter in agricultural soils. To assess the influence of management on soil quality, we characterized the organic matter by measurements of total N, organic C, microbial biomass N and active N in the 0–20cm profiles of soil from long-term field experiments containing plots under treatments of plow or no tillage and 0, 135, or 270kgNha^–1 fertilizer. Previous work had established that on the basis of the crop growth requirement of maize, these application rates of fertilizer N provide amounts of N that are deficient, sufficient, and excessive, respectively. The studies reported provide evidence that the sufficient amount of fertilizer N stimulated formation of the biologically active pools of N (biomass N and active N) in soils under no tillage treatments, but the excessive amount of fertilizer N tended to suppress these pools. The results demonstrated that these influences of excessive N fertilization were not reflected in distributions of total N or total organic C in soil profiles but became evident with the measurements of biologically active N. This suggests that such measurements can provide information related to the influence of different management practices on soil quality. Received: 30 November 1995