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Phosphorus Concentrations in Overland Flow from Diverse Locations on a New York Dairy Farm

Hively, W. Dean, Bryant, Ray B., Fahey, Timothy J.
Journal of environmental quality 2005 v.34 no.4 pp. 1224
phosphorus, pollution load, dairy farming, watersheds, reservoirs, agricultural runoff, rainfall simulation, overland flow, chemical concentration, models, soil types, soil properties, New York
The National Phosphorus Project rainfall simulator was used to quantify overland flow and P transport from nine sites distributed throughout the watershed of a New York City Watershed Agriculture Program collaborating dairy farm. Observed concentrations of total dissolved phosphorus (TDP) were low (0.007–0.12 mg L) in flow from deciduous forest, extensively managed pasture, and hillside seeps; moderate (0.18–0.64 mg L) in flow from intensively managed pastures, a hayfield, and a cow path; and extremely high (11.6 mg L) in flow from a manured barnyard. Concentrations of TDP from sites without fresh manure were strongly correlated with soil test P (TDP [mg L] = 0.0056 + 0.0180 × Morgan's soil test phosphorus [STP, mg kg]; = 84%). Observed concentrations of suspended solids were low (16–137 mg L) in flow from vegetated sites, but were higher (375–615 mg L) in flow from sites with little ground cover (barnyard, cow path, plowed field). Under dry summer conditions the time to observed overland flow was shorter (<18 min) for nonfield areas (seeps, barnyard, cow path) than for field and forest areas (27–93 min), indicating that hydrologically active nonfield areas of minor spatial extent but with high soil P (e.g., cow paths and barnyards) can play a significant role in summertime P loading. When soils started from field capacity (second-day) time to overland flow was uniformly less than 23 min, indicating that under wet watershed conditions low-P source areas can dilute overland flow from concentrated sources.