Nutrient, Carbon, and Mass Loss During Composting of Beef Cattle Feedlot Manure

Quantification ofnutrient andmass loss during composting isneeded ωunderstand the composting process, to implement methods for nutrient conservation, andto reduce potential adverse environmental impact. Beef cattle feedlot manure was composted in a windrow on an open concrete area in 1992, 1993, and 1994 to determine the amounts ofnutrient, C, and mass loss during composting. The area was enclosed onallsides with a 0.2 mhigh metal sheet todirect runoff to a fiberglass tank (捕。o L) during rainfall. Nutrients in runoff represented combined runoff and leaching losses. Nutrients, C, and mass loss during composting was determined by the difference between the amounts at the beginning and at the end of the composting. Nitrogen loss during composting ranged from 19 to42% and was related tothe initial manure Ncontent. Ammonia volatilization (calculated by difference) accounted for >92% oftheNloss whereas combined runoff nitrate and ammonium loss was <0.5%. Mass loss was relatively low (1520%) while C loss ranged from 46 to 62% and was basically all through bio-oxidation. Phosphorus runoff loss, the main mechanism for Ploss,was low «2%). Manure NIP ratio decreased during composting, indicating a greater soil Pbuildup potential with compost application. Potassium and Na losses in runoff were high (>6 .5% each) in 1992and 1993; they were low «2% each) in1994 due tofewer rainfall. Calcium and Mg losses were <6% each year. Nutrient and salt loss during composting resulted in reduced electrical conductivity of the composted manure. Ammonium and Pconcentrations inrunoff would create surface water pollution if runoff was not diluted with fresh water. ABOUT 11 million head of cattle and calves are on feed ~ at any time in the USA (USDA , 1993). About two-thirds of the beef cattle feeding in the USA occurs in Nebraska , Texas , Kansas , Iowa , and Colorado. More than 80% of the fed cattle are produced in feedlots of more than 1000 head capacity (Eghball and Power , 1994). Feeder cattle weighing 230 to 320 kg are normally purchased by or consigned to the feedlot operator, placed on high energy feed for 100 to 180 d , and slaughtered at 450 to 550 kg. Manure is normally cleaned from beef feedlots when animals are marketed or once each year. Manure collected from feedlot is somewhat stable since it has been on the feedlot surface for a long period of time. Typically , in the central and southern Great Plains , manure scraped from beef feedlots becomes mixed with as much as 50% soil and has lost about 50% of its original N content (Eghball and Power , 1994). About 26.4 million Mg of manure is collected annually from all feedlots in the USA. Nitrogen , P , and K in the feedlot B. Eghball, Dep. ofAgronomy, J.F. Power, J.E. Gilley , andJ.W. Doran, USDA-ARS , Univ. ofNebraska, Lincoln, NE 68583. Contribution ofthe USDA-ARS in cooperation with the Nebraska Agric. Exp. Stn. , Lincoln , NE , as paper no. 11208. Received 31 July 1995. *Corresponding author ([email protected]). Published in J. Environ. Qual. 26:189-193 (1997). 189 manure , if all collected and utilized , would have a value of $461 million (Eghball and Power , 1994). Composting manure is a useful method of producing a stabilized product that can be stored or spread with little odor , pathogens , weed seeds, or fly breeding potential (Sweeten, 1988). Composted manure can be applied to soil as an odorless and relatively dry source of nutrients compared with noncomposted manure. Another advantage of composting is improved handling characteristics of manure by reducing volume and weight (Willson and Hummel , 1975). Decomposition of manure occurs through biological action and spontaneous chemical reactions. The initial chemical and biological composition of manure is a function of ration fed, animal age , type of feedlot , and other factors that can influence manure production and decomposition. In composting , N loss through volatilization can be a major problem. The main factors influencing gaseous N loss are total N content of material , temperature, high pH (>8) , and turning (Martins and Dewes , 1992). In a constant temperature/humidity chamber , ammonia volatilization during composting of cattle manure resulted in a 35% decrease in ammonium-N content but total N content was not signi且cantly changed (Stone et al. , 1975). Hansen et al. (1993) reported ammonia loss during composting of poultry manure in reactor vessels to be three times greater with a C/N ratio of 15 compared with 20. In composting mixtures of straw and various kinds of liquid manure (swine, poultry , and cattle) in containers , between46.8 and 77.4%ofthe initial N was lost, primarily as ammonia with a small amount «5%) as NOx (Martins and Dewes , 1992). Nitrogen loss during composting of a sewage sludge-straw mixture resulted primarily from ammonia volatilization (Witter and LopezReal , 1988). In the initial stages of composting , the N loss amounted to 16 to 29% of the initial N content , whereas it was >60 % when composting a limeconditioned sludge with higher initial N content. Compared to fresh manure , 3-mo stabilized farmyard manure had significantly greater concentrations of total N , watersoluble substances, and lignin , and less organic C , lipid, and hemicellulose , as well as a lower C/N ratio (LeviMinzi et al. , 1986). Nitrogen can also be lost from manure in runoff and by nitrate leaching during composting. Relative quantities of N lost by these processes are controlled mainly by site-s Eghball, Power, Gilley & Doran in Journal of Environmental Quality 26 (1997)