Potential of bio-organic amendment of palm oil mill effluent manure and plant growth-promoting bacteria to enhance the yield and quality of maize grains in Cameroon

Achieving soil security is essential to improve maize (Zea mays L.) production that is affected by poor soil fertility, which is often mitigated using chemical fertilizers that cause deleterious environmental effects. The potential of bio-organic amendments to boost soil security was investigated in a field study with eight treatments including; Control–no input, chemical NPK (nitrogen:phosphorus:potassium) fertilizer, Manure (palm oil mill effluent–POME), Microbes (plant growth-promoting bacteria), NPK+Manure, NPK+Microbes, Manure+Microbes, and NPK+Manure+Microbes with four replications each. Results revealed significant (P<0.001) variations in maize grain yield across treatments with the lowest (1.8 tons ha⁻¹) in control, and the highest (3.7 tons ha⁻¹) in integrated treatments of NPK and manure or microbes. A corresponding trend occurred for 1000–maize grain weight that differed significantly (P<0.001) across treatments with the lowest (0.53 kg) in control and the highest (0.62 kg) in integrated treatment of NPK and manure or microbes. Proximate analysis of maize grains revealed significant (P<0.001) increase in protein contents ranging between 0.4–13% across treatments with the highest in the integrated application of NPK+Manure+Microbes. In sum, maize performance was consistent with the significant (P<0.05) increase in soil nitrogen, phosphorus and C-N ratio, with greater effect of microbes, manure and their combination. Earthworm population varied significantly (P<0.001) across treatments with the highest (241 individuals per m³) in manure and the lowest (38 individuals per m³) in NPK treatments. Overall, these results highlight the potential of POME manure and microbes to enhance soil security and boost maize productivity compared to NPK.