1. Dep. of Crop, Soil and Environmental Sciences, Division of Agriculture; Univ. of Arkansas; Fayetteville AR 72701
2. Centre for Ecology and Hydrology, Crowmarsh Gifford; Wallingford OX10 8BB UK
3. USDA-ARS, Pasture Systems and Watershed Management Research Unit; University Park PA 16802
4. Centre for Ecology and Hydrology, Bush Estate, Penicuik; Midlothian EH26 0QB UK