The results from this study clearly demonstrate:- (i) The importance of P in the fertilizer combinations used for maximized soybean production by smallholders in the study area (ii) Better production of the late maturing cultivar SB 20 in the study area (iii) The strong influence of soil carbon level on soybean production within the same farm, although farmers in the study area own relatively small pieces of land and thus the distance between the high carbon and low carbon field was quite small. With the majority of the population in the study area being dependent on the limited agricultural land (requiring no irrigation), improved soybean production by modest application of PKS fertilizers will boost food security and soil fertility in the study area. This will increase crop yields in Kenya and therefore, improve the livelihood of rural populations by offering good and reliable economic returns. Among the most immediate viable strategies as proposed by this study is the amendment of these soils with the currently underutilized organic and inorganic fertilizers and the use of biological nitrogen fixation by legumes. Besides this, new strategies must be defined to connect more closely applied research with the needs of smallholder farmers.