Mineralization of C and N in organic materials as affected by duration of composting

Abstract

The effect of composting fowl manure, grass clippings and brown coal on the subsequent mineralization of C and N from these materials was studied in a glasshouse experiment. Columns of soil were amended with mixtures 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 81 days, CO2 evolved from the soil surface was collected in alkali traps, and N released from the amendments was collected by leaching the columns with distilled water. With the mixtures of fowl manure, grass clippings and brown coal, mineralization of C and N decreased linearly with increasing duration of composting beyond 2 weeks, due to progressive depletion of labile C and N. Mineralization of C and N from the uncomposted 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 potentially mineralizable during the 81 days of the experiment. Leachates collected from the columns contained N in NO-3 , NH+4 and organic forms. Mineralization of C and N was strongly positively correlated. All amendments except brown coal had a positive residual effect on total soil N. The increase was largest in compost treatments but was not related to compost age. All amendments had a similarly small positive residual effect on soil water-holding-capacity.