1. African Fertilizer Summit (2006) African fertilizer summit proceedings, IFDC, Muscle Shoals, AL, USA, p 531
2. Alley MM, Vanlauwe B (2009) The role of fertilizer in integrated plant nutrient management. IFA/TSBF-CIAT, Paris, 59
3. Anderson JM, Ingram JSI (1993) Tropical soil biology and fertility: a handbook of methods, 2nd edn. CAB International, Wallingford
4. Bouyoucos GJ (1962) Hydrometer method improved for making particle size analysis of soils. Agron J 54:464–577
5. Breman H, Groot JJR, Van Keulen H (2001) Resource limitations in Sahelian agriculture. Global Environ Changes 11:59–68