Investigating the Appropriate levels of NPK Fertilizers for Optimum Yield of Soybeans in South West Nigeria

In Nigeria, farmers applied different combination of Nitrogen, Phosphorus and Potassium known as NPK fertilizers to improve the yield which may not be adequately applied at an appropriate levels and this may cause harmful effect on the soil, plants and human. Also, excessive application of chemical fertilizers at times depresses nodule formation and nitrogen fixation in soybeans which retard the growth of the crops and hence, reduce the yield. Therefore, this research seeks to investigate if NPK fertilizers contribute to the yield of soybeans; examine which of the three elements contribute most to the yield; investigates the appropriate levels each of the trio of NPK are to be applied for optimum yield; and estimate the optimal yield of soybeans when applied at an appropriate level. A 3 by 3 factorial design was used to determine if the trio of nitrogen, phosphorus and potassium contribute to the yield of soya-beans, post-hoc analysis were carried out to investigate at what proportion those elements are to be applied, multiple regression model were derived for the optimization of the yield and surface methodology was used to obtain the optimal yield. The result shows that only Nitrogen and Phosphorus contribute significantly to the yield of soya-beans and thus the derived model: Yield = 23.56047 – 12.49669N + 11.45511P - 9.128539K + 8.412062NP + 8.600928NK + 6.808789PK – 6.330242NPK were obtained. Hence, the optimal yield of 76.27tonne/hectare of soya-beans could be obtained if Nitrogen is applied at 90kg, Phosphorus at 90 kg and 0kg of Potassium