Emissions of Ammonia, Nitrous Oxide and Methane during the Management of Solid Manures

Organic manures arising from livestock production provide a source of plant nutrients when applied to agricultural land. However, only about 52% of the N excreted by livestock is estimated to be recycled as a plant nutrient. The ­greatest losses of N from livestock excreta and manures are as gaseous emissions. These emissions are in the form of ammonia (NH3), nitrous oxide (N2O) and methane (CH4). Ammonia forms particles in the atmosphere which reduce visibility and may also harm human health, and when deposited to land NH3 causes nutrient enrichment of soil. Nitrous oxide and CH4 contribute significantly to global warming and N2O can also cause the breakdown of the protective ozone layer in the upper atmosphere. We established a database of emissions from solid manures. Statistical analysis provided new information, focussing on developing emission factors, emission algorithms and also new understanding of emission patterns from solid manure. The review found that housing systems with deep litter emit more NH3 than tied stalls. This is likely to be because the emitting surface area in a tied stall is smaller. Laying hens emit more NH3 than broilers and reduced-emission housing systems for poultry, including the aviary system, can reduce NH3 emissions by between 50% and 80%. The greatest N2O-N emissions from buildings housing livestock were also from deep litter systems, but the amount of N2O-N was smaller than that of NH3-N by a factor of 15. Air exchange and temperature increase induced by aerobic decomposition during manure storage may greatly increase NH3 emission. Emissions of 0.25–0.30 of the total-N have been recorded from pig and cattle manure heaps undergoing aerobic decomposition. Increased density of manure during storage significantly decreased temperatures in manure heaps. Storing solid manures at high density also reduces air exchange which with the low temperature limits the formation and transfer of NH3 to the surface layers of the heap, reducing emissions. Most N2O emission estimates from cattle and pig manure have been between 0.001 and 0.009 of total-N. Emission of N2O from poultry manure tends to be small. Average unabated NH3 emissions following application of manure were 0.79, 0.63 and 0.40 of total ammoniacal-N (TAN) from cattle, pig and poultry manure respectively. The smaller emission from poultry manure is expected as hydrolysis of uric acid to urea may take many months and is often incomplete even after application, hence limiting the potential for NH3 emission. Manure incorporation within 4 h after application reduced emission on average by 32%, 92% and 85% for cattle, pig and poultry manure respectively. Reductions following incorporation within 24 h or more after application were 20%, 56% and 50% for cattle, pigs and poultry, respectively. Incorporation by disc or harrow reduced NH3 emissions less than incorporation by plough. Emissions of N2O following the application of cattle manure were 0.12 of TAN without incorporation after application and 0.073 TAN with incorporation after application. Conversely, emissions following application of pig and poultry manures were 0.003 and 0.001 TAN respectively without and 0.035 and 0.089 TAN respectively with incorporation after applicatio