Author
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Stout, William |
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Submitted to: Agriculture, Ecosystems & Environment
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 2/25/2003 Publication Date: 10/20/2003 Citation: Stout, W.L. 2003. Effect of urine volume on nitrate leaching in the northeast u.s.. Agricultural Ecosystems and Environment. 67(2):197-203. Interpretive Summary: The United States Environmental Protection Agency has adopted the concept on total maximum daily load (TMDL) of a contaminant (i.e. nitrate) in the water at the outlet of a watershed to determine if the watershed is impaired. Determining the contribution of nitrate leaching loss from the urine of animals grazing upland pastures to the TMDL at a watershed outlet can only be determined through the combined use of animal metabolic, plant growth, soil leaching, and hydrologic transport models. However, such models need experimental data for development, calibration to local soils and geology, and validation over time. To provide such data, we measured nitrate leaching loss from 3 different volumes of cow urine applied to the soil. This represents the range of urine volume of the different breeds of dairy cattle. We found that nitrate leaching increased with urine volume but that urine volume had no significant effect on the fraction of nitrate leached. This simplifies the modeling process because urine N output from animal metabolic models can be expressed in animal units for each class of livestock (i.e. milking cows, dry cows, etc.), without regard to size differences due to breed. Also, the effect of urine volume in nitrate leaching can be considered to be a constant in soil leaching models. Technical Abstract: Management intensive grazing (MIG) is a grazing system in which animals at a high stocking density are rotated through several paddocks at short time intervals (12-24 hours) so that animal performance is maximized. Although MIG has the potential to increase dairy farm profitability in the northeast U.S., recent lysimeter studies in this region have shown that a substantial lamount of NO3-N applied as urine is leached below the root zone. Projecting the lysimeter studies over a pastured landscape indicates that water quality standards may not be achieved, even at normal stocking rates. However, these projections were made from data based on a single volume of urine application. How the urine volume (i.e. size of cow) affects how much NO3-N is leached from a urine deposition in the climatic conditions of the northeast U.S. is not known. We conducted a field study using large drainage lysimeters to measure NO3-N leaching loss from synthetic urine applied in 1, 2, and 3-l volumes to an orchardgrass (Dactyls glomerata L., c.v. 'Pennlate') sward. The study site was located in central Pennsylvania on a Hagerstown silt loam soil (fine, mixed, mesic Typic Hapludalf). We found that over the range of urine volume treatments in this study, the effect of urine volume on NO3-N leaching loss was linear, and thus the fraction of N leached from a urine deposition remained constant at about 25% of the urine applied. This greatly simplifies the use of models to predict the impact of grazing on water quality. |