Mineralization of composted manure and microbial dynamics in soil as affected by long-term nitrogen management

Evaluation of the mineralization dynamics of composted manures is essential for their efficient use as a major source of available nitrogen in crop production. The objective was to determine the effect of long-term management on the rate of mineralization of compost, in relation to soil biological activity. A compost was added at a rate of 5 or 15% (wt/wt) to soil samples obtained from two treatments of a 30 year old N-management experiment: M0—without any N input, and M2—with 10 applications of 90 t cattle manure ha−1. Inorganic N accumulation and weekly rates of CO2 evolution were determined periodically during an incubation of 33 weeks. Microbial counts and dehydrogenase and protease activity were determined during 42 days. Net N mineralization was higher in M2 than in M0 soil, and was proportional to the amount of compost added. The recovery of compost-N as inorganic N was independent of soil management history and of compost application rate. The amount of N released was estimated (by difference) to be 26% of compost N added. Initially 7–10% was inorganic N and 8% soluble organic N, therefore only 8–11% was released from insoluble N in the compost. CO2 evolution was greater from M2 than from M0 soil only during the first week, but it was significantly affected by compost application throughout the experiment. The percentage recovery of compost-C as CO2 was smaller at the high application rate. Microbial counts and enzyme activities exhibited a periodical behavior. They were significantly affected by soil management history, and by compost, but the effect of compost was greater. The difference in biological activity between soils seemed to be related to the difference in their initial readily-available C and it did not significantly affect the rate of compost decomposition.