Assessing the Effect of Grass Filter Strips on Edge-of-Field Phosphorus Runoff Losses in Wisconsin.
Laura Good1, John Norman2, and Carlos Bonilla2. (1) 1525 Observatory Dr., University of Wisconsin-Madison, UW-Madison, 163 Soils Building, Madison, WI 53706-1299, (2) Soil Science Dept, UW-Madison, 1525 Observatory Dr, Madison, WI 53706-1299
On two cropped fields with 45-foot grass filter strips, runoff was collected above and below the filter strips year-round for three years and analyzed for sediment, dissolved phosphorus (DP), and total P (TP). The first year of monitoring included extremely large spring and early summer storms at both sites, while in the second year there was comparatively little spring and summer runoff and most of the runoff occurred during the winter. Field A had a sandy loam soil on a steep (10%) slope and was in corn silage for most of the study period. The other field had clay loam soil, was not as steep (5% slope), and was in corn for grain. Field A lost more sediment and P than Field B in both years. Over a two-year period, the grass filter strips captured 66% and 83% of the sediment but only 60% and 28% of the TP on fields A and B respectively. Over the winter (frozen soil period) of the second year, the filter strip area on field B because a source rather than a sink for TP. The proportion of field runoff sediment and phosphorus that will be retained in a filter strip varies with the proportion of finer particles in the runoff and thus varies with crop, field management and season. This research helps to identify the conditions where filter strips are appropriate management options and where they may not be as beneficial. The results are being used to assess grass filter strip effectiveness at reducing P delivery to surface water for Wisconsin.