Journal of Agricultural Science and Practice

Neem seed cake has been reported to make nutrients available to support good growth of crops and increase yield. This ease of nutrient release is also required in a potential bio-stimulant. This study assessed the potentials of a neem seed-based fertilizer formulation as a bio-stimulant to aid continued nutrient mineralization from an organic source in contaminated soil samples. Neem seed-based organomineral formulation was added to soil samples contaminated with two field rates (40 and 60 mg.a. i ha^-1) of nicosulfuron herbicide to assess their separate and interaction effects on soil microbial activity in the laboratory. The treated samples were incubated for 8 weeks, and soil microbial activity was monitored in dynamics for the period of incubation. Data on soil basal respiration, soil organic carbon, and soil carbon mineralization quotient (qM) were collected on weekly basis for the 8 weeks. Application of nicosulfuron alone regardless of rate repressed soil basal respiration; hence carbon mineralization in the early weeks of the incubation period, but these parameters were stimulated after the 5th week of incubation. Addition of the neem formulation on the other hand caused consistent significant stimulation from the beginning to the end of incubation. Results further showed that combining nicosulfuron and the neem formulation raised soil basal respiration significantly above what individual factor contributed. It was therefore concluded that although the individual factor was found to increase CO₂-C compared to the control at the end of incubation, the interaction of the two inputs raised CO₂-C even higher. This is an indication that the neem seed cake formulation has the potentials to cushion the adverse effects of nicosulfuron contamination on the soil microbial community.