Author
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Stout, William |
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Submitted to: Nutrient Cycling in Agroecosystems
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/20/2003 Publication Date: 4/1/2003 Citation: Stout, W.L. 2003. Effect of urine volume on urine n cycling. Nutrient Cycling in Agroecosystems. 34(7&8):945-955. Interpretive Summary: In order to improve farm profitability, the practice of management intensive grazing is being adopted by small- and medium-sized dairy farms in the northeast U.S. But substantial amounts of nitrate from urine deposition on pastures can be leached into the ground water from this practice. This paper is part of a series of experiments to quantity factors that affect nitrate leaching from pastures. Previous experiments have shown that the amount of nitrate leached is affected by such things as soils, weather, and animal stocking density. This paper quantifies the affect of urine volume (i.e. animal size) on plant accumulation of urine N, its subsequent affect on urine N leaching, and the effect on previous estimates of urine N leaching. We found that while urine volume directly affected the amount of urine N accumulated by pasture plants, it did not affect the earlier estimates of the amount of nitrate that could be leached dfrom pastures. This represents another step in the further development of an index to predict the total maximum daily loads (TMDL) from pastures. The TMDL concept is being adopted by U.S. EPA to determine the extent to which watersheds are impacted by nonpoint source pollution. Technical Abstract: Management intensive grazing (MIG) has the potential to increase dairy farm profitability in the northeast U.S., but recent lysimeter studies in this region have shown that a substantial amount of NO3-N applied in cattle urine is leached below the root zone. Projecting the results of these 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 accumulated by pasture herbage and how this accumulation subsequently affects the amount of NO3-N that is leached from a urine deposition in the climatic conditions of the northeast U.S. is not known. We conducted a two field study to determine the impact area from synthetic urine applied in 1, 2, and 3 l volumes to a predominantly orchardgrass (Dactyls glomerata L., c.v. 'Pennlate') sward. Dry matter yields and apparent urine N accumulation (AUNA) data indicated that urine N affected plant growth out to 50 cm from the point of deposition. However, percent apparent urine N accumulation (PAUNA) out to 50 cm was similar to PAUNA in the previously reported work in which urine N was applied to 60 cm diameter (30 cm radius) drainage lysimeters. Therefore, we conclude that restriction of urine application to a 60 cm diameter lysimeter did not appreciably affect the amount of residual urine N in the soil that would be subject to leaching. Consequently, urine N leaching data developed from 60 cm diameter drainage lysimeters can reliably be used to predict NO3-N leaching at a field or landscape scale. |
