Gaseous NO, NO2, and NH3 Loss During Cattle Feedlot Manure Composting

The emission of NH3 and NOx gases during feedlot manure composting reduces the agronomic value of final compost as a soil amendment. In addition, NOx gases cause air smog and deplete stratospheric ozone. The effect of passive aeration treatment (no turning) and active aeration treatment (turned 6 times) on NH3 and NOx emission during composting of feedlot manure was investigated in open windrows in summer 1997. The atmospheric concentrations of NH3, NO and NO2 at the windrow surface and 50 cm above were monitored throughout the composting period (99 days). Composting increased the atmospheric concentration of NH3 and NO, while NO2 was not affected. The atmospheric NH3 concentration was higher during early composting and decreased with the composting period for both aeration treatments. Active aeration resulted in a much higher early NH3 concentration (5500 ppb) than passive aeration (1000 ppb) at the windrow surface, but there was little difference later in the composting. The lower NH3 loss for the passive aeration treatment is consistent with the higher N retained in the compost at the end of the experiment. The atmospheric NO concentration increased up to 350 ppb at the surface of the passive aeration windrow during early composting, then decreased to much lower values (< 50 ppb) around day 50 and stayed low for the rest of composting period. Similar NO atmospheric concentration patterns were observed for the active aeration treatment, but the early NO concentration was much lower. Since the decomposition of manure/compost materials was incomplete for the passive aeration treatment, further studies are needed to investigate possible techniques to reduce NH3 and NO losses (retaining more N in the finishing compost) while increasing the composting rate. INTRODUCTION Livestock production in southern Alberta has experienced major changes in recent years and cattle feedlots of 10,000 head and larger are now common (Lethbridge County 1998). Associated with the increased intensity of livestock operations is the increased amount of feedlot manure produced each year. Proper utilization of manure is crucial to the long-term sustainability of feedlot operations. Traditionally, cattle manure is directly applied to nearby fields. However, this has created concern over environmental issues such as nitrate leaching to the groundwater (Chang & Janzen 1996). The composting of feedlot manure has been proposed as an alternative to direct land application. Composting produces a stabilized product that can be stored or spread on land with little or no odor, pathogens, weed seeds, or fly breeding potential (Rynk & al. 1992). Compost may also be trucked further distances since composting significantly reduces volume and mass (Larney & al. 2000). Composting is a biological process in which organic matter is transformed into humus-like materials. But this process also releases various gaseous N compounds into the atmosphere, reducing the agronomic value of compost as a soil amendment and