Mineralization of nutrients from soil microbial biomass

Soil samples of parabrown earth and chernozem, each having a different amount of microbial biomass, were used to investigate the contribution of microbial cells to the pool of mobile plant nutrients in soils. The quantities of nutrients mobilized in soils which had been dried or fumigated were closely related to the quantities available in freshly-killed biomass. For the percent of N mineralized from dead microbial biomass in arable soil during 28 days, a “k_N-factor” (28 days) of 0.37 was suggested. In oven-dried (70°C) and air-dried (room temperature) soils, approximately 77 and 55% of the N mineralized after remoistening and incubating at 22°C for 4 weeks came from the freshly-killed biomass. The remaining 23 and 45% were derived from non-biomass organic N fractions of the soils. In fumigation experiments (CHCl₃, 24 h), the amount of P released was closely related to the P content of the soil microbial biomass. The fluctuating amounts of K available after fumigation did not correspond to the amount of biomass killed. A scheme for the transformation of dead microbial biomass-C and -N in arable soil is suggested.