Optimized vermicomposting of a goat manure-vegetable food waste mixture for enhanced nutrient release

Abstract In arid countries, goats are the preferred small livestock and these generate dung that has can be used as manure to improve the soil quality. Furthermore, in arid countries like Namibia, most of the fruit and vegetables are imported, and during transportation damage and deterioration may occur which results in losses. Our study seeks to optimize the vermicomposting of goat manure and vegetable food waste to generate a nutrient rich organic fertilizer using Eisenia fetida earthworms. The influence of various ratios of vegetable food waste (FW) and goat manure (GM) mixtures on vermi-degradation and plant nutrient release was evaluated. There were significant differences (P 50FW:50GM > control (100GM) > 25FW:75GM. Similarly, the 75FW:25GM and 50FW:50GM treatments had the highest final concentration of Olsen phosphorus of 0.98 and 0.96 g per kg of compost, respectively. Relative to the control, the treatments with 75%; 50% and 25% FW resulted in a 113%; 109% and 60% more Olsen phosphorus, respectively, after 12 weeks of vermicomposting. There were no significant differences (P > 0.05) across all treatments on nitrate/nitrite concentrations following 12 weeks of vermicomposting. The changes in plant available P and N during vermicomposting were predictable using second order polynomial equations. A compost mixture of the ratio 75FW: 25GM or 50FW:50GM will give an optimized vermicompost for plant P nutrition after about 10 to 12 weeks of vermicomposting.