Volatilization of ammonia, nitrous oxide and nitric oxide in deep-litter systems for fattening pigs

In a deep-litter housing system, animals are kept on a thick layer of a mixture of manure with sawdust, straw or woodshavings. In this study, sawdust was used for two different deep-litter systems for fattening pigs (System 1 and 2). The differences between the systems were the amount of litter per pig, the size of the sawdust particles and the way the bed was treated. From manure, NH3 (ammonia) can volatilize. In a mixture of manure and sawdust the microbial processes, nitrification and denitrification can occur which convert NH3 into the inert N-2 (dinitrogen gas). If conditions are suboptimum and these processes do not run to completion, the air-polluting volatile intermediates N2O (nitrous oxide) and NO (nitric oxide) are emitted. Field studies were carried out to obtain values for the concentrations in the exhaust air of NH3, N2O and NO. Ventilation rates were measured and emissions of these air-polluting nitrogen gases calculated. The results were compared with the emission of a traditional system with manure storage under a fully slatted floor of 0.3 g N/h per pig as NH3. The nitrogen emitted as NH3, NO and N2O measured with System 1 was 0.24, 0.04 and 0.3 g N/h per pig respectively. For System 2 emissions were 0.12, 0.01 and 0.2 g N/h per pig respectively. System 2 tends to reduce the ammonia emission compared with traditional housing systems (P = 0.078) but for System 1 there was no difference. In both systems, the emission of total air-polluting nitrogen was not reduced compared with a traditional house, System 1 had increased N emission (P < 0.05). From both systems most of the air-polluting nitrogen was emitted as N2O, although for System 2 this was not significant. In a laboratory study, samples of the deep-fitter beds were incubated under various O-2 concentrations to study under which conditions N2O was produced in the deep litter. The results showed increasing N2O emission with decreasing O-2 concentration in the bed, indicating that N2O is mainly produced in the course of nitrification. It is concluded that deep-litter systems for fattening pigs may reduce NH3-emission compared with housing on fully slatted floors, but emissions of air-polluting nitrogen gases Lend to be higher due to the formation of N2O. From an environmental point of view, these two deep-litter systems are therefore not recommended. (C) 1996 Silsoe Research Institute