Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2009
Publication Date: 10/1/2009
Citation: Cole, N.A., Mason, A., Todd, R.W., Rhoades, M., Parker, D. 2009. Chemical composition of pen surface layers of beef cattle feedyards. Professional Animal Scientist. 25:541-552. Interpretive Summary: The effects of concentrated livestock feeding operations such as beef cattle feedyards on air and water quality are a growing concern among livestock producers, regulators, and the general public. A large proportion of the nutrients cattle consume are eventually excreted in feces and urine and deposited on the feedlot surface. These nutrients are transformed and modified by microbial activity and physical processes such as compaction, wetting and drying, etc. The chemical and physical processes that occur may have a major effect on the losses of nutrients such as nitrogen to the air or water. Because of these processes four distinct layers usually form on the surface of feedlot pens: 1) a loose layer comprised mostly of small manure particles, 2) a dry-hard packed layer mostly of manure, 3) a damp hard-packed layer mostly of manure, and 4) the underlying soil. These layers may contain different inorganic forms of nitrogen that may affect the quantities of ammonia emitted to the atmosphere and nitrates that may leach to groundwater. The purpose of this experiment was to determine the chemical composition of these layers in typical commercial feedyards and to evaluate the effects of factors such as season, pen location, urine, proximity to water troughs, days on feed, and manure mounds on the total nitrogen, ammonium-nitrogen, nitrate-nitrogen, and carbon concentrations, as well as the pH and electrical conductivity. The chemical composition of the layers were significantly affected by the pen surface layer, season of the year, and urine spots but, in general, were not appreciably affected by pen location, mounds or proximity to water troughs. In general the results suggest that the hard-pack layers form a barrier that prevents infiltration of water and nutrients into the soil layer and thus helps to prevent percolation of nutrients to ground water under the feedyard. Thus, a major portion of the excreted nitrogen is lost as ammonia to the atmosphere; whereas little is lost as nitrates to groundwater.
Technical Abstract: The biological, physical, and chemical characteristics of beef cattle feedyard pen surfaces may affect nutrient transformations and losses to the atmosphere, ground water, or surface water. Feedyard pen surfaces can typically segregate into three or four layers. The purpose of this study was to determine if there were seasonal, within-pen location, days-on-feed, and/or urine effects on the chemical composition of the pen surface layers of feedyards. Samples were collected from five locations in nine pens at three feedyards in each season and were analyzed for gravimetric water, pH, electrical conductivity (EC), nitrate+nitrate-N (NOx-N), ammonia+ammonium-N (NHx-N), N, C, and P. The percent water increased (P < 0.01) with depth among the manure layers and decreased in the soil. The pH of the manure layers increased with depth (P < 0.01) from approximately 7.9 to 8.2. The EC of the manure layers was greater (P < 0.01) than the soil layer; whereas, the NOx-N concentrations were greatest (P < 0.01) in the soil layer. The NHx-N concentrations were lowest in the soil layer (P < 0.01). Total C and N concentrations decreased (P < 0.01) with sample depth. The composition of the layers was affected by season and location within the pen. Recent urine deposition did not affect lower layers. The NHx-N concentration of the layers increased with days-on-feed. The differences in the chemical and physical properties of the layers in a feedlot pen may potentially affect nutrient losses to the atmosphere and to groundwater.