Addition of mineral fertilizer to an organic source of nutrients may reduce the lag between application to the soil and nutrient release. A field experiment laid out as randomized complete block design was conducted at the Teaching and Research Farm of the Federal University of Technology, Akure Nigeria to compare the effects of organic, mineral and an organo-mineral fertilizer formulations on soil microbial population, chemical properties and maize (Zea mays) performance. Treatments involved three soil amendments, which were: NPK at 250kg/ha; Neem seed-based fertilizer (NSBF) at 300kg/ha, and Compost at 2.5 t/ha. Treatments also included a Control where the soil was not amended at all. At maize harvest, plant height appeared in the order of NSBF > NPK > Compost > control, and they caused 15.9, 15.8 and 6.1 % increases, respectively. Other growth and yield parameters were also affected by the various treatments in similar manner as the plant height. Result also showed that while the Compost and NSBF increased microbial count (both bacteria and fungi), growth of microorganisms was repressed by the application of NPK fertilizer. Soil pH, organic carbon (OC) as well as residual nitrogen, phosphorus and potassium concentrations were significantly increased by both Compost and the NSBF whereas application of mineral fertilizer reduced their concentrations in the soil at the termination of the experiment. It was therefore concluded that organomineral formulations can serve dual purposes of both quick nutrient release as well as leave residual nutrients in the soil for the following cropping.