1. USDA‐ARS Pasture Systems & Watershed Management Research Unit University Park PA 16802 USA
2. USDA‐ARS Southeast Watershed Research Lab. Tifton GA 31793 USA
3. USDA‐ARS Jornada Experimental Range Las Cruces NM 88003 USA
4. USDA‐ARS Grassland Soil and Water Research Lab. Temple TX 76502 USA
5. Dep. of Animal Science The Pennsylvania State Univ. University Park PA 16802 USA
6. USDA‐ARS Sustainable Agricultural Systems Lab. Beltsville Agricultural Research Center Beltsville MD 20705 USA
7. USDA‐ARS Soil Management and Sugarbeet Research Unit Fort Collins CO 80526 USA