Microbial biomass as a fraction of potentially mineralizable nitrogen in soils from long-term field experiments

• Published in: Soil biology & biochemistry 1988, Vol.20 (4), p.447-452
• Main Authors: Bonde, Torben A., Schnürer, Johan, Rosswall, Thomas
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; biomass production; Chemical, physicochemical, biochemical and biological properties; correlation; cropping systems; experimental plots; Fundamental and applied biological sciences. Psychology; microbial activity; nitrogen mineralization potential; Organic matter; Physics, chemistry, biochemistry and biology of agricultural and forest soils; soil management; Soil science; tillage
• ISSN: 0038-0717; 1879-3428; 1879-3428
• DOI: 10.1016/0038-0717(88)90056-9

Aerobic long-term incubations (40-wk) were employed to measure the potentially mineralizable nitrogen (N 0) in five 30-yr old cropping systems. The cropping systems consisted of: (1) bare fallow; (2) cropping with no additions; (3) cropping with 80 kg N ha −1 y −1 as Ca(NO 3) 2; (4) cropping with 80 kg N ha −1 yr −1 as Ca(NO 3) 2 plus 1800kg C ha −1 yr −1 as straw; and (5) cropping with 80 kg N ha −1 yr −1 plus 1800 kg C ha −1 yr −1 as farmyard manure. The amounts of N mineralized during the 40-wk incubations were between 93 and 168 μg g −1 (302–543 kg N ha −1 down to 25cm depth) with the lowest value for the fallow and the highest for the farmyard manure treatment. Microbial biomass-C and -N were measured on four occasions during the incubations. The biomass-C showed a rapid decrease to week 4 (to 36% of the initial mass), a slower decrease to week 9 (to 23% of initial mass) and a very slow decline to the final determination at the end of the incubation (to 8% of initial mass). The biomass-N displayed a similar pattern. Two related models were employed to describe the kinetics of N-mineralization during incubation: (1) a two-component first-order; and (2) a simplified special case of the two-component model. In all cases except the straw-amended soil, the simplified two-component model offered the best description of the curves of accumulated mineral-N. The available fraction, N a, of soil organic-N had mineralization rate constants similar to those for mineralization of microbial biomass.