Decomposition of organic matter and mineralization of nitrogen in brookston silt loam and alfalfa green manure

Summary C¹⁴ and N¹⁵ doubly labelled alfalfa tissue at addition rates of 5 and 1 ton per acre was incubated in the laboratory for 72 days with virgin and cultivated Brookston silt loam. The alfalfa tissue was more extensively decomposed in the virgin soils than in cultivated soil, but retention of tissue carbon was not affected by rate of addition. Percentage decomposition of organic matter in the virgin soil was greater than that in the cultivated soil. Addition of alfalfa tissue reduced decomposition of soil organic matter in proportion to the rate of addition and resulted in a gain of carbon in the incubation mixture. No priming action was noted.An increase in the rate of tissue addition caused an increase in the amount of nitrogen mineralized from the tissue but had little effect on the amount of nitrogen mineralized from the soil. Nitrogen mineralized from the soil organic matter was preferentially immobilized during the latter part of the incubation period.It appears that the organic matter content of the soil as well as the rate of tissue addition may regulate the priming action of green manures.Published with approval of the Director, Ohio Agricultural Experiment Station as Journal Paper No.94-62.