Quality of runoff from plots with simulated grazing

Grazed pastures represent a potential source of nonpoint pollution. In comp arison to other nonpoint sources (e.g., row-cropped lands), relatively litt le information exists regarding possible magnitudes of nutrient losses from grazed pasture, how those losses are affected by management variables, and how the losses can be minimized. The objective of this study was to measur e concentrations of nitrogen (N), phosphorus (P), and solids in runoff from fescue plots and relate those measurements to simulated forage management strategy. The study was conducted at the University of Kentucky Maine Chanc e Agricultural Experiment Station north of Lexington. Plots (2.4 m wide by 6.1 m long) were constructed and established in Kentucky 31 fescue (Festuca arundinacea Schreb.) to represent pasture. The experimental treatments app lied to the plots varied in terms of forage height and material applied (no ne, manure, or manure and urine). Runoff was sampled for six simulated rain fall events applied over the summer of 1997 and analyzed for nitrate N (NO3 -N), ammonia N (NH3-N), total Kjeldahl N (TKN), ortho-P (PO4-P), total P (T P), and total suspended solids (TSS). All runoff constituents exhibited dep endence on the date of simulated rainfall with generally higher concentrati ons measured when simulated rainfall followed relatively dry periods. The e ffects of forage height and manure addition were mixed. Highest runoff N co ncentrations were associated with the greatest forage heights, whereas high est P concentrations occurred for the least forage heights. Manure/urine ad dition increased runoff P concentrations relative to controls (no manure/ur ine) for both the greatest and least forage heights, but runoff N concentra tions were increased only for the greatest forage heights. These findings i ndicate that runoff of N and P is at least as sensitive to amount and proxi mity of preceding rainfall and suggest that managing forage to stimulate gr owth and plant uptake can reduce runoff of N.