1. Univ. of Florida Range Cattle Research and Education Center 3401 Experiment Station Ona FL 33865
2. Soil and Water Science Dep. Univ. of Florida P.O. Box 110290 Gainesville FL 32611
3. Center for Nuclear Energy in Agriculture Univ. of Sao Paulo Av Centenario, 303 Piracicaba 13416‐000 Brazil
4. Agronomy Dep. Univ. of Florida P.O. Box 110500 Gainesville FL 32611‐0500