Vermicomposting of agro-based waste in central Kenyan highlands

Abstract

In Central Kenyan Highlands, soil nutrients pose a challenge to farmers in this area due to continuous cultivation of the soils. As a result, there is need to explore farmers' easily available resources for utilization on their farms. For instance, Central Kenyan Highlands' forest litter has indigenous epigeic earthworms with a potential to hasten degradation of agricultural wastes. The epigeic earthworm populations and their ability to degrade organic waste were examined. The objective; to validate the existence and populations of the indigenous epigeic earthworm was used to check for the presence of epigeic earthworms in the forest was in Muguga, Kinale and Uplands forests. Three methods namely litterbag, quadrate and monolith in combination with three feeds; cow-manure, wheat bran and forest litter were used. Epigeic earthworm population densities were found to be between 130,000-220,000 worms ha' while the cocoons density was 380,000- 620,000 ha' during the rainy season depending on the availability of litter in the Central Kenyan Highlands. For proper utilization of the earthworms, identification of a good energy and nitrogen source for Eisenia foetida's multiplication in different agricultural wastes namely cow manure, banana stalks, coffee waste and maize stover was carried out. The epigeic earthworms trapped were used to produce vermicomposts based on the objective to evaluate the rate and efficiency of conversion of organic wastes into vermicompost by the Indigenous epigeic earthworms and the exotic Eisenia foetida species; and to examine the chemical characteristics of the produced vermicomposts. Both indigenous and exotic earthworms were fed on a mixture of maize stover, banana stalks, bean trash, coffee waste & husks, and cow manure in well-aerated custom raised wooden boxes. Other treatments were desiccation and composting. All the treatments were replicated three times in a completely randomized design. A feed volume of 0.25m3 and starter worm population of 500 was used per box. The vermicomposting process was carried out for 112 days. Chemical characteristics available Nitrogen, Phosphorus, Potassium, Calcium, Magnesium and Cation Exchange Capacity (CEC) increased while Sodium and organic Carbon Decreased with time. A fourth objective was to study the nutrient release characteristics of the vermicomposts produced. This was accomplished using leaching and mineralization of the vermicomposts over time. The leaching trends were based on amount of organic fertilizer added, type of fertilizer and the sampling time. In the treatments used Nitrates decreased from 0.43 fl9/9 to a steady 0.07 fl9/9 while the ammonium decreased from 0.34 to 0.11 fl9/9 indicating that the decrease was more in nitrates than the ammonium. Later in the experimentation the vermicomposts were taken to the green house to evaluate their agronomic effectiveness as an organic nutrient source for kale production. This experiment showed that the vermicomposts at 10 tons ha' performance as an organic fertilizer was comparable to a commercial fertilizer Oiammonium phosphate (OAP) at 60 kg N ha'. Similar trend was exhibited by the biomass production of the kales. Key words: Earthworms, worms, organic waste, compost, vermicomposting, composting, Eisenia toetide, indigenous, epigeic, quadrate, Iitterbag, forest, trapping, vermicomposts, leaching, mineralization and kales.