ASSESSING WOODY PLANT SPECIES COMPOSITION AND DIVERSITY AND EVALUATING THE EFFECT OF CORDIA AFRICANA LAM. AND CROTON MACROSTACHYUS HOCHST.EX DELILE TREES ON SOIL PROPERTIES AND LITTER DECOMPOSITION IN PARKLAND AGROFORESTRY IN BULLEN DISTRICT, METEKEL ZONE, NORTHWESTERN ETHIOPIA

Abstract

Trees in farmlands are believed to affect soil properties and agricultural productivity, yet farmers are often limited in their choice of agroforestry tree species. This study aimed to quantify the effect of tree species on soil properties and litter decomposition, as well as assess woody species composition and diversity in parkland agroforestry in Bullen District, Metekel Zone, northwestern Ethiopia. A 10*20m Plots were systematically established along line transects in farmlands to assess woody species compostion, diversity, and structure. A randomized complete block design (RCBD) was used to quantify soil properties and litter decomposition rates under C. africana and C. macrostachyus, separately, across five blocks (farmlands). In each farmland, soil samples were collected from under three mature individuals of C. africana and C. macrostachyus at 0-20cm soil depth from three concentric radial distances from the tree trunks (at 1/3 of crown, 2/3 of crown, and 3 times crown radius). The same procedure was followed for the litter decomposition experiment where leaf litters of Cordia africana (C. africana) and Croton macrostachyus (C. macrostachyus) were buried for three months while being retireived every month. All data were analyzed using SAS software (Version 9.0) following the Proc Mixed Procedure, and mean separation was done with Tukey’s HSD test (α>5%). A total of 34 woody species belonging to 17 families were identified, with C. macrostachyus, C. africana, F. sur, and T. laxiflora dominating most of the farmalnds. All soil variables such as OC(%), TN(%), AP(ppm), pH & CEC(meq/100g) were affected by distance from the tree trunk, showing significant decreasing trend as increased distance from tree trunk while all except pH and CEC, were also influenced by tree identity. Soil organic carbon, available phosphorus, and total nitrogen were higher under C. macrostachyus compared to C. africana. Litter decomposition was also significantly influenced by tree identity, distance, and incubation period. The % mass loss was significantly higher near the tree canopy than in open cultivated areas, with C. macrostachyus showing higher % mass loss compared to C. africana. In conclusion, C. africana and C. macrostachyus trees in parkland agroforestry seem to improve soil nutrient status through litter addition and improving rate of litter decomposition