Nitrogen and Carbon Mineralization Dynamics of Manures and Composts

Abstract

Nitrogen and carbon mineralization rates of 19 manure and compost samples were determined in 1996, with an additional 12 samples evaluated in 1997. These organic amendments were mixed with a soil: sand blend at 2% by dry weight and the amended blends were incubated at constant moisture for 12 (1996) or 24 weeks (1997) at 25 °C. Net N mineralization was measured at 4- (1996) or 8-week (1997) intervals, C mineralization at 4-week intervals in 1997. Pots of the amended blends were also seeded with fescue (Festuca arundinacea Shreb.) and watered, but not fertilized, for 17 (1996) or 18 weeks (1997); N phytoavailability was estimated from fescue biomass N and mineral N in pot leachate. An average of 16%, 7%, and 1% of organic N was mineralized in 12 weeks of incubation in 1996, and an average of 15%, 6%, and 2% in 24 weeks of incubation in 1997, in manure, manure compost, and plant residue compost, respectively. Overall, N recovery in the fescue assay averaged 11%, 6%, and 2% of total amendment N for manure, manure compost, and plant residue compost, respectively. Mineralization of manure C averaged 35% of initial C content in 24 weeks, while compost C mineralization averaged only 14%. Within 4 (compost) or 16 weeks (manure), the rate of mineralization of amendment C had declined to a level similar to that of the soil organic C.