1. International Fertilizer Development Center (IFDC); International Rice Research Institute (IRRI) Cooperative Project; P.O. Box 933 Manila Philippines
2. Agronomy, Physiology, and Agroecology Div., IRRI; P.O. Box 993 Manila
3. Isotope Lab.; Division of Agricultural Chemistry, Dep. of Agriculture; Bangkok 10900 Thailand
4. Sukamandi Research Inst. for Food Crops; Jln. Raya no. 9 Sukamandi Subang West Java Indonesia