Volatilization of Ammonia, Nitrous Oxide and Nitric Oxide in Deep-litter Systems for Fattening Pigs

Abstract

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, NH 3(ammonia) can volatilize. In a mixture of manure and sawdust the microbial processes, nitrification and denitrification can occur which convert NH 3into the inert N 2(dinitrogen gas). If conditions are suboptimum and these processes do not run to completion, the air-polluting volatile intermediates N 2O (nitrous oxide) and NO (nitric oxide) are emitted. Field studies were carried out to obtain values for the concentrations in the exhaust air of NH 3, N 2O 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 NH 3. The nitrogen emitted as NH 3, NO and N 2O 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 N 2O, although for System 2 this was not significant. In a laboratory study, samples of the deep-litter beds were incubated under various O 2concentrations to study under which conditions N 2O was produced in the deep litter. The results showed increasing N 2O emission with decreasing O 2concentration in the bed, indicating that N 2O is mainly produced in the course of nitrification. It is concluded that deep-litter systems for fattening pigs may reduce NH 3-emission compared with housing on fully slatted floors, but emissions of air-polluting nitrogen gases tend to be higher due to the formation of N 2O. From an environmental point of view, these two deep-litter systems are therefore not recommended.