Field studies were conducted in the early and late season of 2010 in the tropical rainforest zone of Nigeria to investigate the effects of NPK fertilizer as an inorganic soil amendment at 75 kg/ha and 150 kg/ha in four replications on population densities of Pratylenchus brachyurus and on crop yield of maize. Seeds of maize variety, DMR LSR-Y were collected from Institute of Agricultural Research and Training, Ibadan. The experimental field was naturally infested with Pratylenchus spp. due to subsequent continuous cultivation of susceptible crop on the field. Seeds were planted and NPK was applied around the roots of maize plants 3 weeks after seedling emergence. Soil samples were taken on treatment plots at planting and harvest to determine the percentage change in nematode population. At the end of experiment, NPK application resulted in the increase in the nematode population. However, the grain yield of maize was not reduced by the increased nematode densities. The results of this study suggests that the usage of NPK caused a surge in the nematode reproduction on the field due to the availability of more feeding sites on the actively growing root system of the crop.