Narrow grass hedge effects on phosphorus and nitrogen in runoff following manure and fertilizer application

Runoff losses of nitrogen (N) and phosphorus (P) from field applied manure can contribute to surface water pollution. Grass hedges may reduce runoff l osses of nutrients and sediment The objective of this study was to evaluate the effects of narrow switchgrass (Panicum virgatum L.) hedges (similar to 0.75 m wide) on the transport of P and N from afield receiving beef cattle feedlot manure under tilled and no-till renditions. This study was conduct ed on a steep (12 % average slope) Monona silt loam (fine-silty, mixed, sup eractive, mesic Typic Hapludolls) soil near Treynor, Iowa. The experiment w as a split-plot with no-till and disked systems as main plots and subplots of manure, fertilizer and check with or without a grass hedge. A rainfall s imulator was used and runoff was collected from both the initial and the fo llowing wet simulations. Only 38% of the no-till plots and 63% of disked pl ots had any runoff during the initial 6.4 cm hr(-1) water application. A si ngle narrow grass hedge reduced runoff concentrations of dissolved P (DP) b y 47%, bioavailable P (BAP) by 48%, particulate P (PP) by 38%, total P (TP) by 40%, and NH4-N by 60% during the wet simulation on the no-till plots re ceiving manure, compared with similar plots with no hedges. The correspondi ng reductions in concentrations as a result of a grass hedge for DP, BAP, P P, TP, and NH4-N on the disked plots were 21, 29, 43, 38, and 52%, respecti vely. Runoff NH4-N concentration from fertilizer applied to the disked plot s was reduced by 61%, NO3-N by 21%, and total N (TN) by 27% during the wet simulation when grass hedges were used. Grass hedges also reduced total qua ntities of DP, BAP, TP, and NH4-N during the wet simulation. The TP loss wa s 3.3% of applied P fertilizer and was 0.3% of applied manure P. Narrow gra ss hedges were effective in reducing P and N losses in runoff from both man ure and fertilizer application.