1. Dep. of Ecosystem Science and Management Pennsylvania State Univ. University Park PA 16802 USA
2. Dep. of Crop and Soil Sciences North Carolina State Univ. Raleigh NC 27695 USA
3. Agriculture and Environment Center Pennsylvania State Univ. University Park PA 16802 USA
4. Pasture Systems and Watershed Management Research Unit USDA Agricultural Research Service University Park PA 16802 USA