Ninhydrin Reactive Nitrogen of CHCl3 Fumigated and Non Fumigated Compost Extracts as a Parameter to Evaluate Compost stability

Three compost, from widely different composting processes (a garden compost and two municipal plants for solid waste treatment), were investigated for their biomass C and ninhydrin-N content at different stages of the compo sting period. Biomass C in all the 3 compost reached a maximum at the end of the thermophilic phase, maintained a high content throughout the mesophilic phase and then decreased with a trend that roughly parallels temperatureBiomass ninhydrin-N showed a regular decreasing trend during the whole composting period. A similar behaviour was observed for non fumigated ninhydrin-N. This parameter, reflecting the release of extracellular enzymes and the intensity of ammonification processes, could represent itself a useful parameter to evaluate compost stability.The ratio between biomass C and ninhydrin-N increased in the first month of the process and decreasing afterwards to values within the range normally found in soils (14–33), suggesting a change in the composition of microbial population during composting process.The percentage of biomass ninhydrin-N respect to total N, showed lower values in stabilized compost respect to compost in the early stage of decomposition. The trend observed in the 3 different composting processes, suggests that a low C_bio/nin-N_bio together with a ninhydrin-N_bio content about 1 % of the total N would indicate a well stabilized compost.