MINERALIZATION OF C AND N IN ORGANIC MATERIALS AS AFFECTED BY DURATION OF COMPOSTING

The effect of composting fowl manure, grass clippings and brown coal o n the subsequent mineralization of C and N from these materials was st udied in a glasshouse experiment. Columns of soil were amended with mi xtures of these materials which had been composted for 0, 2, 4, 8, 12 or 16 weeks, or with each material alone. Periodically over the next 8 1 days, CO2 evolved from the soil surface was collected in alkali trap s, and N released from the amendments was collected by leaching the co lumns with distilled water. With the mixtures of fowl manure, grass cl ippings and brown coal, mineralization of C and N decreased linearly w ith increasing duration of composting beyond 2 weeks, due to progressi ve depletion of labile C and N. Mineralization of C and N from the unc omposted mixture was similar to that from compost aged 4 weeks. Brown coal contributed neither C nor N in an available form. Around 70% of N in fowl manure and grass clippings and 11-34% of N in compost was pot entially mineralizable during the 81 days of the experiment. Leachates collected from the columns contained N in NO3-, NH4+ and organic form s. Mineralization of C and N was strongly positively correlated. All a mendments except brown coal had a positive residual effect on total so il N. The increase was largest in compost treatments but was not relat ed to compost age. All amendments had a similarly small positive resid ual effect on soil water-holding-capacity.