The result of experiments are given in table 2, the result obtained from each sample shows that, the concentration of phosphorus in each of the sample is higher compared to nitrogen, while the concentration of potassium is in trace. This a clear indication that biofertilizer produced from watermelon peel is a phosphorous solubilizing biofertilizer and Nitrogen fixing biofertilizer. ANOVA results for the cubic model were shown in Where N.P.K content is the response and the coded term A and B represent retention days and water ratio. It can be seen from the model equation that the linear terms A and B, and the interaction term AB in equation 4.1 and 4.2 are positive which denote positive contribution to N-content and P-content, while the quadratic and cubic terms A 2, B 2 A 3 B 3 and A 2 Bare negative, which denote negative contribution to both N and P content. While for equation 4.3, it could be seen that the cubic quadratic terms A 2 B 2 and A 3 are positive, which denote positive contribution to K-content. While the interaction term AB and A 2 B is negative which denotes negative contribution to K-content. From the numerical solution obtained these solution were picked which gave an optimum values, which are retention days20.00, water ratio4.01, N content26.2824, P content94.5099 and K content0.000495515.