**2. Materials and Methods**

#### *2.1. Research Site*

This study was conducted at the University of Wisconsin/USDA-ARS Marshfield Agricultural Research Station near Stratford, WI. The fields are mapped as somewhat poorly drained Withee silt loam (fine-loamy, mixed, superactive, frigid Aquic Glossudalfs; 1–3% slope). These soils have a dense, compacted B-horizon at approximately 50 cm resulting in high runoff potential. The 30-year average annual temperature and precipitation at the site are 6.9 ◦C and 831 mm, respectively. The site is comprised of four forage crop production fields separated by earthen berms directing runoff to individual flumes, with each field functioning as a small watershed. Each field is approximately 1.6 ha and are referred to individually as M1, M2, M3, and M4. The average field slope is approximately 2% for M1, M2, and M4. The average slope for field M3 is 0.25% for the lower third of the field area and 3% for the upper 2/3 of the field. The lower area of M3 is more imperfectly drained with visible standing water after heavy rainfall and snowmelt events. More details on site establishment and calibration period (2006–2008) results are presented in Jokela and Casler [39].
