Cassava Yield and Economic Response to Fertilizer in Tanzania, Kenya and Ghana

Cassava (Manihot esculenta Crantz) is a major food crop in Africa with little information of response to applied nutrients. Our objectives were to: determine cassava yield response to macronutrients for production areas in Ghana, Kenya and Tanzania; evaluate the effect Mg, S, Zn and B application; and determine agronomic efficiency (AE) and value cost ratio (VCR) for nutrient application. Fresh storage root yield with no fertilizer averaged 14.4 Mg ha(-1) and mean yield increases due to 80 kg ha(-1) N applied were 8.1, 6.5 and 9.0 Mg ha(-1) in Ghana, Kenya and Tanzania. Storage root yield was increased 93% with P application for Aduma in Ghana and there was a curvilinear to plateau response to K at Wenchi Ghana. No other responses to P and K rates occurred, but an N x P synergism occurred in Tanzania. There were no responses to applied Mg, S, Zn, and B. The VCR for N at all sites was >2 indicating sufficient profit opportunity to make N application attractive to many financially constrained farmers. The mean soil organic C (SOC) was 8 g kg(-1); the results may lose applicability with much higher SOC soils. Over all trials, application of 80 kg ha(-1) N had, on average 8.44 Mg ha(-1) increased yield with 105 kg kg(-1) agronomic efficiency and 7.8 $ $(-1) profit to cost ratio. The results indicate that cassava is efficient in P and K uptake with restricted and little profit potential for P and K application in these countries, respectively.