Determination of economically optimal rates of Fertilizer use and implications in Irish potato production in Kenya.
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This study is on determination of economically optimal fertilizer rates in Irish potato production for four agro-ecological zones (AEZs) in Kenya, namely Upper Midland-2 (UM2), Lower Highland-3 (LH3), Lower Highland-I (LHI) and Upper Highland-2 (UH-2). Experimental yield data from the Fertilizer Use Recommendation project(FURP) was used. The sites under study were Chehe and Muirungi for LH I, Kerugoya and Kaguru FTC for UM2, Tulaga and Njabini for UH2 and 01 Ng'arua and Eldama Ravine for LH3. Potato yields from 16 different fertilizer rates were computed over the years and an average yield taken. Primary data was also obtained by interviewing farmers using a structured Questionnaire. The primary data obtained was on the fertilizer rates the farmers use, the fertilizer type and costs, costs associated with fertilizer use, and the potato yield achieved. The experimental and primary data were all combined using a formula to determine the economically optimal fertilizer rates. These calculated rates were compared to the rates that farmers use. Results show that the economically optimal fertilizer rates are significantly different from the fertilizer rates that farmers use and that certain nutrients are applied in some areas where economic analysis shows that these nutrients should not be used if profit maximisation has to be achieved. In conclusion, the Irish potato growing farmers do not use fertilizer rates that achieve maximum or near maximum profit.