Determination ofin situ KN by the chloroform fumigation-incubation method and mineralization of biomass N under anaerobic conditions

A silt loam soil from Pakistan was incubated at 30°C with increasing levels (67, 133, 200, 267 and 333 μg N g^?1 soil) of¹⁵N-labelled (NH₄)₂SO₄ and glucose (C/N ratio of 30 for all additions). At a stage when all of the applied¹⁵N was immobilized (transformed into microbial biomass), moist soil samples were subjected to the chloroform fumigation-incubation method (CFIM) for determination of K_N and microbial biomass. Mineralization of biomass derived from the applied¹⁵N and the native soil N was studied under anaerobic conditions. In situ values of K_N varied from 0.19 to 0.42 and increased with increasing levels of amendment (N + glucose). From 10 to 18% of the native soil N was found as microbial biomass. Anaerobic incubation of the soils resulted in the mineralization (determined as NH ₄ ⁺ ) of 15.08 to 29.23% of the biomass¹⁵N at different levels of amendment; 2.90 to 4.43% of the native soil N was mineralized. From 70 to 90% of the N mineralized from native soil N was derived from microbial biomass; the rest was attributed to non-biomass N.