Characteristics of ammonia volatilization and nitrous oxide emission of different fermentation beds in pig pens

Different forms of nitrogen (N) in nature are important in both crop and animal agro-ecosystems. N is not only a valuable resource in agro-economics, but also the by-product of animal husbandry which could cause eutrophication of water environment via nitrogen overload and global warming via nitrous oxide (N₂O) emissions. In animal husbandry, nitrogen is ingested as a valuable resource of protein in feeds and left the system as fertilizer or waste. In large scale pig farming in China, ammonia (NH₃) volatilization has been responsible for odd smells in surrounding environments. Recent development of fermentation bed technology (FBT) in large scale pig farming systems has partially addressed concerns relating to reducing NH₃ volatilization and N₂O emission. It was hypothesized that different compositions of fermentation beds had different effects on NH₃ volatilization and N₂O emission in this study. To justify the hypothesis, the characteristics of NH₃ volatilization and N₂O emission of three different fermentation beds rice husk + sawdust (FD), rice husk + mushroom bran (FJ) and rice husk + vinasse (FW) available in large quantities in farmlands were investigated. Gas samples were collected by static box method during one production cycle (140 d). The experimental conditions and basic environmental factors (e.g., water content, physical and chemical properties of fermentation bed) were recorded and analyzed. The results showed that NH3 volatilization in the three beds had different patterns. NH₃ volatilization peak appeared earliest at the feeding period in FW, followed by FJ and then finally FD. The total amounts of NH₃ volatilization in three beds during the experimental period were significantly (P < 0.05) different. Of the three treatments, the largest amount of NH₃ volatilization was FW (9.06 kg), followed by FJ (4.83 kg) and then it was lowest in FD (3.82 kg). The three beds were consistent in the patterns of N₂O emission and N₂O emission peaks were mainly at mid-anaphase of the feeding period. The total amounts of N₂O emission were significantly (P < 0.05) different; of which it was highest in FW (2.06 kg), followed by FJ (1.74 kg) and then finally FD (1.50 kg). Material flow analysis showed that N gas (NH₃ and N₂O) loss accounted for 23% 36% of total N loss. The results revealed that the main path ways of N loss were via nitrogen transformation into NH₃ or N₂O during the production cycle of pig fermentation beds. This suggested that FJ performed the best in terms of composition.