Tree Diversity Effects on Litter Decomposition in an Agroforestry System in a Semi Arid Zone in Juja, Kenya

Abstract

Plant litter decomposition is an important ecosystem function that aid nutrient cycling in agroforestry system, however it is not clear if the diversity of agroforestry tree species affects rate of decomposition of their resultant litters within the early stage of decomposition. This study was conducted in an agroforestry experimental farm that was established in 2011 in Jomo Kenyatta university of Agriculture and Technology, Juja, Kenya. The site contains four treatments involving seven agroforestry tree species from which eleven combinations was grouped for decomposition process. The decomposition process was studied using the standard litter bag technique and the soil moisture content on each treatment plot was measured to determine its confounding effect on litter decomposition.  The percentage mass loss of litter after 90 days of decomposition was highest in Acacia seyal (48.75%) and lowest in Cordia africana (21.65%). The composite litter decomposes faster than the low decomposing monocultures suggesting synergistic interaction but when the observed and predicted litter mass loss was compared a 100% additive effect was observed. The treatment plots with Faidherbia albida had the highest soil moisture content (42.97%) while the treatment plots with C. africana had the lowest (28.96%). However, effect of soil moisture was not significant on the rate of decomposition (r²=0.046). These findings suggest that litter combination increases rate of decomposition in low decomposing litters and soil moisture effect was insignificant on rate of decomposition, suggesting other factors are contribution to decomposition. Farmers should therefore use different agroforestry species to benefit from the synergy of the different ecosystem function of different tree species such as enhanced decomposition rate from the low decomposing species.

Keywords: Agroforestry; Decomposition; Nutrients; Soil moisture; Synergistic.