DECOMPOSITION AND NUTRIENT RELEASE PATTERN OF THREE AGROFORESTRY SHRUB SPECIES FOLIAGE AT DELLO-MENNA DISTRICT OF BALE ZONE, SOUTHEAST ETHIOPIA

The main input of nutrients in agroforestry system is achieved through decomposition of tree biomass, mainly from foliage litter. Foliage litter sourced from tree component shows considerable quality variation among species. Hence, better management and sustainable production within agroforestry land use system remain on the selection of tree/shrub species having efficient nutrient return capabilities through decomposition of foliage litter. A study was conducted to determine the rate of decomposition and nutrient release pattern of Cajanus cajan, Sesbania sesban and Flemingia macrophylla foliage litters, using litter-bag technique at Sinana Agricultural Research sub-site of Dello-menna district, Bale. The experiment was installed using split-plot 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 species. The relationship between rates of constant and biochemical composition was examined using Pearson’s correlation coefficient. Results showed that, the fastest decomposition rate was 0.037 day-1 for S. sesban followed by 0.017 day-1 for C. cajan and the least 0.014 day-1 for F. macrophylla with t respective 18.72, 40.76 and 49.5 days taken to loss 50% of original dry matter. A considerable amount of nutrients were added to the soil from decomposed foliage litters. At the end of the study, more than 87% of the initial nutrients were released into the soil except for Carbon. Carbon was released within a range of 43.2 to 57.94%. The observed variation in rate of decomposition and nutrient release among the species was due to the resultant effects of their biochemical composition. Lignin, Cellulose, Lignocelluloses index and C/N ratio were identified as impeding biochemical parameters whereas Phosphorus and Nitrogen were identified as facilitators. Among the species, S.sesban was reported to be the best species to return higher amount of nutrients within a short period of time followed by C.cajan and F.macrophylla, respectively. But, the accelerated decomposition of S.sesban may limit its potential for long-term build-up of soil fertility. Alternatively, F.macrophylla majorly and C.cajan in some case should be considered for long-term build-up of soil organic matter