Submitted to: Applied Engineering in Agriculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2004
Publication Date: 5/1/2005
Citation: Baker, K.D. 2005. Temporal assessment of nutrient contributions to waterways from feedlots. Applied Engineering in Agriculture. 21(3):517-528. Interpretive Summary: This project is aimed toward reducing nutrient and organic carbon levels in surface waterways. The focus of the model is feedlots with stocking rates equivalent to up to 250 steers per hectare (100 steers per acre), such as is common in the Midwestern U.S. The equations that have been developed can be incorporated into computer spreadsheets or models. The computer programs can be used to assess nutrient contribution from a feedlot to a waterway on a daily basis and sum them over any specified time period. Animal producers will benefit by being more knowledgeable concerning their individual operations and will be able to manage them more effectively. Regulation agencies will benefit by being able to locate the more troublesome operations and allocate their resources to get the most benefit from environmental improvement efforts. Scientists will benefit by the additional knowledge that will become available in the literature. The general public will benefit from a cleaner environment and the return of fish and other aquatic animals that may have been killed or left the region due to low dissolved oxygen as a result of excess nutrients in surface waterways.
Technical Abstract: Equations were developed to compute nutrient contributions on a daily basis to waterways from feedlots with stocking rates equivalent to up to 250 steers per hectare (100 steers per acre), such as is common in the Midwestern U.S. The overall algorithm uses recorded weather data (daily values) and other input values and reports nutrient amounts and concentrations in runoff, considering spatial and temporal aspects. Methodology to divide a large feedlot which contains more than one drainage outlet was determined, so that the described algorithm may be used for any size feedlot. Equations from USDA, Natural Resources Conservation Service were adapted to determine curve numbers for frozen soil, or soil of any moisture, as well as to determine runoff from rainfall and snowmelt events. Equations from ASAE were adapted to determine manure production from temporally changing animal loads on the feedlot and to compute temporal changes in the manure pack on the feedlot. Equations from USDA, Agricultural Research Service were adapted to determine nutrient concentrations in runoff for each runoff event. Equations were developed to incorporate mechanical removal of waste from a feedlot, as well as to include decomposition of nutrients on the feedlot. Previously used equations were revised to determine nutrient reduction in feedlot buffer regions and due to dilution from mixing stream flows. The algorithm described in this study was verified for mathematical stability and accuracy by programming them in a spreadsheet program and checking results.