Fate of nitrogen during composting of chicken litter

Chicken litter (a mixture of chicken manure, wood shavings, waste feed, and feathers) was composted in forced-aeration piles to understand the changes and losses of nitrogen (N) during composting. During the composting proces s, the chemical [different N fractions, organic matter (OM), organic carbon (C), and C:N ratio], physical, and microbial properties of the chicken lit ter were examined. Cumulative losses and mass balances of N and organic mat ter were also quantified to determine actual losses during composting. The changes in total N concentration of the chicken litter piles were essential ly equal to those of the organic N. The inorganic N concentrations were low , and that organic N was the major nitrogenous constituent. The ammonium (N H4+)-N concentration decreased dramatically during first 35 days of compost ing. However, the rapid decrease in NH4+-N during composting did not coinci de with a rapid increase in (NO3- + NO2-)-N concentration. The concentratio n of (NO3- + NO2-)-N was very low (< 0.5 g kg(-1)) at day 0, and this level remained unchanged during the first 35 days of composting suggesting that N was lost during composting. Losses of N in this composting process were g overned mainly by volatilization of ammonia (NH3) as the pile temperatures were high and the pH values were above 7. The narrow C:N ratio (<20:1) have also contributed to losses of N in the chicken litter. The OM and total or ganic C mass decreased with composting time. About 42 kg of the organic C w as converted to CO2. On the other hand, 18 kg was lost during composting. T his loss was more than half (59%) of the initial N mass of the piles. Such a finding demonstrates that composting reduced the value of the chicken lit ter as N fertilizer. However, the composted chicken contained a more humifi ed (stabilized) OM compared with the uncomposted chicken litter, which woul d enhance its value as a soil conditioner. (C) 2000 Elsevier Science Ltd. A ll rights reserved.