NITROGEN AND CARBON MINERALIZATION RATES OF COMPOSTED MANURES INCUBATED IN SOIL

Rates of decomposition and inorganic N release from composted manures should be known and predictable on the basis of their composition for their proper use as a source of available N. Four composted cattle man ures were analyzed for their inorganic N, soluble organic C and N, and total N and organic matter contents. The composts were incubated in s oil for 32 wk at 30 degrees C and 60% water-holding capacity. Inorgani c N and CO2 evolution were determined periodically. Inorganic N releas ed from the composts after 32 wk ranged from 11 to 29% of their total N content, 2 to 12% of total N were initially inorganic, and 1 to 5% w ere soluble organic N. The rates of decomposition of the composts were computed by the simulation model NCSOIL by minimizing the deviation o f the model output from the periodically measured CO2 and inorganic N release and by using the soluble and insoluble organic C and N content s of the composts as input. The soluble components decomposed before t he end of the first week. The decomposition rate constant obtained for the insoluble components of three composts was 4 to 5 x 10(-4) d(-1), whereas for one compost it was 1 x 10(-8) d(-1), indicating that this compost was much more stable. To obtain universal rate constants that will fit any compost, components of the insoluble material must be be tter defined.