As managed intensive rotational grazing (MIRG) becomes a growing trend in Wisconsin, it is necessary to understand the environmental impacts from this management strategy, particularly impacts originating from over-wintering areas.
This study was conducted, in conjunction with water quality monitoring, to determine spatial and temporal variations in vegetation and soil characteristics within MIRG over-wintering areas on two MIRG farms with different soils in Wisconsin.
From October 2005 through August 2006, four vegetation events (October 2005 and May, June, and August 2006) and one surface (0-2.5 cm) soil sampling event (October 2005) were conducted on a 28 acre over-wintering area on the Columbia County farm and an 18 acre over-wintering area on the Manitowoc County farm. Vegetation measurements included forage yield, leaf area index, and stem density. Soil measurements included surface roughness, constant rate cone pentrometer, and soil analyzes for nitrogen and phosphorus.
Strong linear relationships were observed between forage yields and stem densities on the Columbia County farm in October 2005 (R2 = 0.85) and May 2006 (R2 = 0.82) and on the Manitowoc County farm in May 2006 (R2 = 0.87). Leaf area index (LAI) was strongly correlated (R2 = 0.89) with stem density on the Manitowoc County farm in May 2006, and LAI was strongly correlated with forage yield (R2 = 0.97), on the Columbia Cty farm in August 2006.
Average soil nitrate levels were 56 ppm (40-81 ppm) and 64 ppm (39-83 ppm) and average available phosphorus levels were 15 (8.7-20 ppm) and 25 (8.4-61 ppm) on the Columbia County and Manitowoc County farms, respectively. Strong relationships (R2 > 0.8) were observed between NH4 and stem density, NH4 and Bray P, OM and TP, OM and Bray P, and TP and Bray P on the Manitowoc County farm and OM and TN on the Columbia County farm.