1. Soil and Plant Nutrition Division, Fertilizer Research Programs, International Fertilizer Development Center (IFDC), Muscle Shoals, AL, USA;
2. Agriculture Technology Transfer Project, International Fertilizer Development Center (IFDC), Tamale, Ghana;
3. Africa Rice Center (AfricaRice), C/O International Fertilizer Development Center (IFDC), Tamale, Ghana;
4. Savanna Agricultural Research Institute (SARI), Tamale, Ghana