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 a mount 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 a nd denitrification can occur which convert NH3 into the inert N-2 (din itrogen gas). If conditions are suboptimum and these processes do not run to completion, the air-polluting volatile intermediates N2O (nitro us oxide) and NO (nitric oxide) are emitted. Field studies were carrie d out to obtain values for the concentrations in the exhaust air of NH 3, N2O and NO. Ventilation rates were measured and emissions of these air-polluting nitrogen gases calculated. The results were compared wit h the emission of a traditional system with manure storage under a ful ly 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 pe r 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 o f 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 u nder which conditions N2O was produced in the deep litter. The results showed increasing N2O emission with decreasing O-2 concentration in t he bed, indicating that N2O is mainly produced in the course of nitrif ication. It is concluded that deep-litter systems for fattening pigs m ay 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 Res earch Institute