The potential of fermented cottonseed oil-mill effluent as inexpensive biofertilizers and its agronomic evaluationon medium-textured tropical soil

Purpose Upsurge of oil-mill industries and associatedgeneration of wastewaters constitutes a huge environmentalproblem in Nigeria. As an option to reckless disposal,such effluents are often fermented and used as biofertilizersfor nutrient-poor soils, but the potential of cottonseed oilmilleffluent (COME) and agronomic evaluation of suchpotential has yet been studied.Methods A pot trial was conducted in northern Nigeria toassess the effects of COME fermented for 20 days andapplied at five rates (0, 50, 100, 150 and 200 g 5-kg-1 soil)on soil fertility 2 weeks after application and performanceof African Spinach over the next 5 weeks.Results Soil pH increased steadily from 7.5 in unamendedsoil (control) to 8.0 at the maximum rate of fermentedCOME. Soil organic matter showed similar trend; from16.7 to 27.7 g kg-1. Also, soil available nitrogen, availablephosphorus and exchangeable potassium all indicatedlowest values (0.28, 4.36 and 8.25 mg kg-1, respectively)in the control and the values increased steadily withincrease in COME rate up to 0.47, 24.94 and29.75 mg kg-1, respectively, at the maximum rate. Bycontrast, plant height, leaf area, number of leaves and freshleaf yield of spinach were highest in the control anddecreased with increase in COME rate until total inhibitionof plant growth at C150 g 5-kg-1 soil.Conclusion Fermentation of COME for 20 days before usepermits the expression of its fertilizer value in soil; however,the fermentation level attained within this periodtranslates into a sub-optimal detoxification status that is toolow for crop growth.