Effects of Litter Diversity of Selected Tree Species on Decomposition in an Agroforestry System in Semi-Arid, Kenya (A Case Study of Juja)

Abstract

Plant litter decomposition is an important ecosystem function that aid nutrient cycling in an ecosystem. However, there is little information on how diversity of agroforestry tree species affects the rate of decomposition of their resultant litter. This study was conducted on an established agroforestry experimental farm in JKUAT, Kenya. The site contains three treatments and a control, using seven agroforestry tree species from which eleven compositions of litter were made. Decomposition process and nutrient released was studied using the standard litter bag technique. Litter fall from the tree species was collected using conical litter traps to determine ecosystem nutrient release. Soil moisture content on each treatment plot was measured to determine its confounding effect on litter decomposition. The average biomass loss in litter of the compositions after 90 days of decomposition was highest in litter of Acacia seyal (48.75%) and lowest in Cordia africana (21.65%). The observed and the predicted litter biomass loss and nutrient released when compared, additive effect was observed in biomass loss of all tested mixtures. Additive effect was also observed in Nitrogen, Phosphorus and Potassium released but a non-additive effect was observed in Carbon released. A. seyal had the highest litter fall and released the highest nutrient of N, P, K and C (23, 1.33, 3.0 and 127 kg ha-1 N, P, K and C respectively). Treatment plots with Faidhebia albida had the highest soil moisture content (42.97%) while C. africana plot had the lowest (28.96%). However, the effect of soil moisture was not significant on the rate of decomposition (r2=0.046). The mixed compositions decomposed faster than the low decomposing monocultures suggesting synergistic interaction. The findings from this study show that tree diversity increases rate of decomposition and nutrient release from low quality tree litter. The rate of decomposition and nutrient released in mixed compositions was regulated by individual species rather than species richness. There are other factors that aid soil moisture in litter decomposition. In conclusion, farmers should therefore use different agroforestry tree species to benefit from the synergy of the different ecosystem function that tree species could render such as enhanced decomposition and nutrient cycling from the low quality tree species.