Absorption of nitrogen by Japanese mint from mineralization and immobilization by the soil microbial biomass

Laboratory incubation and greenhouse experiments were conducted with two soils having contrasting physico-chemical characteristics to evaluate nitrogen (N) mineralization, immobilization in soil microbial biomass, and accumulation in Japanese mint (Mentha arvensis L.) using labeled ((NH4)-N-15)(2)SO4, applied at 0, 50, and 100 mg.kg(-1) soil. Rate of mineralization in soils varied from 0.08 to 2.21 mu g.g(-1).day(-1). Fertilizer application increased the mineralization of native soil N. About 22 to 60% of the applied N-15 was recovered in the soil microbial biomass during the growth period of mint (January-June). Relative contribution of fertilizer N-15 towards total N uptake by mint at maturity was 42-54% in soil I and 35 to 55% in soil II. Contribution of soil N towards total N accumulation increased with the doses of N-15 application.