LITTER DECOMPOSITION RATE AND NUTRIENT RELEASE PATTERN OF SELECTED INDIGENOUS AGROFORESTRY TREE SPECIES, JIMMA ZONE, SOUTH WESTERN ETHIOPIA

The selection and use of appropriate Agroforestry tree species to maintain a sufficiently high nutrient supply to meet crop needs remains a major challenge of nutrient management under low input farming systems. Therefore, research on C. macrostachyus, F.vasta and E.abyssinica foliage litter quality as it relates to decomposition and nutrient release has become very important. A study was conducted to determine the rate of decomposition and nutrient release pattern from foliage litters of C.macrostachyus, F.vasta and E.abyssinica using litter-bag technique at Boye Nursery site, Jimma Environment and Forest Research Center. The experiment was installed using RCBD design; considering species types as main plot and incubation period (15, 30, 45, 60, 75 and 90 days) as sub-plot factors. In the study, single exponential model was employed to determine rates of decomposition and nutrient release of the foliage. The relationship between rates of constant and biochemical composition was examined using Pearson’s correlation coefficient. Results showed that, C. macrostachyus decomposed significantly faster than both F.vata and E.abyssinica with rate constant (k) of 0.0400 day-1 (C. macrostachyus) and 0.0233 day-1 for both F.vata and E.abyssinica with t respective 17.3 and 29.7 days taken to loss 50% of original dry matter. Considerable amounts of nutrients were added to the soil from decomposed foliage litters. At the end of the study, more than 89.35% of the initial nutrients were released into the soil. The observed variation in the rate of decomposition and nutrient release among the species was due to the resultant effects of their biochemical composition. Cellulose and C/N ratio were identified as impeding biochemical parameters whereas Phosphorus and Nitrogen were identified as facilitators. Among the species, E.abyssinica reported to be the best species to return higher amount of nitrogen within a short time period followed by C.macrostachyus and F.vasta, respectively. The accelerated decomposition of C.macrostachyus may limit its potential for long-term build-up of soil fertility. Alternatively, E.abyssinica majorly and F.vasta in some cases should be considered for long term build-up of soil organic carbon