Factors influencing nitrogen mineralization during poultry litter composting and calculations for available nitrogen

Abstract

This paper describes, under laboratory and/or field conditions, an approach that could be used to predict nitrogen (N) mineralization of poultry litter. Proper composting of poultry litter results in N mineralization, reducing or eliminating the environmentally harmful effects of ammonia (NH3) odours and nitrate leaching. Addition of straw to poultry manure provides sufficient available carbon and increases NH3 binding capacity, overruling any greater influence of diet composition on methane (CH3) formation. C:N ratio ranges (6–25) vary in the amount of low N loss depending on substrates. Aerobic decomposition of manure results in formation of humified organic compounds and decreased nutrient availability, while anaerobic decomposition forms low molecular weight compounds (volatile fatty acids and NH3 +- N). The differences in the size of the composted particles results in physical separation and decomposability of high and low C:N ratio substrates. Temperatures ranging from 14 to 35°C did not affect the rate of N mineralization, but affected N loss from poultry manure pellets by decay nitrification at 14 and 35°C compared with 25°C. Uric acid and undigested proteins in poultry litter have optimal degradation rates at pH of 5.5 or higher, with the optimum pH for uricase being about 9. Variations in manure composition are seen between different species such as cattle, swine and poultry. The chemical composition of the manure and not the substrate N status influences the rate of decomposition or microbial availability. The N mineralization potential of some vegetable residues correlated better with the total and water soluble N contents than with their C:N ratios. Poultry manures are applied to agricultural soils at rates determined by the amount of available N that they are assumed to contribute to the crops. Many equations have been developed to calculate these application rates.