SOIL BIOTA AND MICROBIAL BIOMASS CARBON UNDER DIFFERENT AGROFORESTRY PRACTICES IN CENTRAL AND SOUTHREN ETHIOPIA

Abstract

The conversion of natural ecosystems for agricultural expansion is changing the world‘s landscapes in pervasive ways. The severity of land degradation in southern Ethiopia has been increasing because of population pressure, where the replacement of agroforestry practice with monoculture based agricultural systems is becoming a trend. This conversion of natural lands to agricultural uses is a significant threat to soil biodiversity, soil structure, glomalin and biomass carbon of microbes. This study aimed to: (1) analyze arbuscular mycorrihizal fungi species diversity, spore density, and root colonization across different agroforestry practices, (2) determine the effect of agroforestry practices on glomalin related soil protein, mean weight diameter, soil aggregate stability size distribution and soil aggregate associated soil organic carbon, (3) analyze soil macrofauna abundance and diversity across different agroforestry practices and (4) analyze the distribution of soil microbial biomass carbon across different agroforestry practices in southern Ethiopia. We collected soil and root samples from experimental units of homegarden based agroforestry practices, parkland based agroforestry practices, woodlot agroforestry practices, and trees on soil and water conservation measures based agroforestry practices from two soil depth categories (0-30 cm & 30-60 cm). Arbuscular mycorrihizal fungi spores were extracted from the soil and species diversity was evaluated using morphological analysis and root colonization from root samples. To determine glomalin related soil protein, Bradford dye binding assay and bovine serum albumin as the standard solution were used. Soil monolith sample was used to identify the samples of soil macrofauna and then the soil macrofauna abundance and diversity was analyzed based on morphological characteristics and standard identification keys. The microbial biomass carbon was determined using the difference in fumigated and non-fumigated extracted carbon contents. We identified 43 arbuscular mycorrihizal fungi morphotypes belonging to 11 genera which were dominated by Acaulospora (32.56%) followed by Claroideoglomus (18.60%) and Funneliformis and Glomus (9.30%). The highest spore density (7641.5 spore100 g-1 dry soil) and the lowest were recorded (683.6 spore100 g-1 dry soil) in homegarden agroforestry practices and parkland agroforestry practices, respectively, and the highest root colonization (54.75%) were observed under woodlot agroforestry practices. In this study, the highest isolation frequency (63.63%) was registered for Acaulospora scrobiculata, and the distribution of AMF species and diversity were significantly related to soil total nitrogen and organic carbon. Our findings revealed that the easily extractablexxi glomalin related soil protein, total glomalin related soil protein, dry and wet mean weight diameter were significantly (p < 0.05) higher in homegarden agroforestry practices and woodlot agroforestry practices compared to parkland agroforestry practices and trees on soil and water conservation agroforestry practices. Moreover, the significant positive relationship was observed between glomalin related soil protein and bulk soil in both soil depths. We have found positive and significant relationship between the fraction of macro and microaggregate soil organic carbon contents with mean weight diameter values. Similarly, it was indicated that the positive and significant relationship between the distributions of different sized soil aggregate stability classes with macro and microaggregate soil organic carbon contents. On the other hand, we have identified 378 soil macrofauna individuals belonging to 13 families and 11 orders (excluding unidentified), including some unidentified soil macrofauna in the study area where it was dominated by earthworms (relative abundance = 0.43) followed by termites (relative abundance = 0.21) and ants (relative abundance = 0.12). Homegarden agroforestry practices had a significantly higher number of soil macrofauna occurrence index of 46.03 (174) and woodlot agroforestry practices with occurrence index of 26.72 (101) while, the lowest was found under parkland agroforestry practices with occurrence index of 12.70 (48). The highest contents of microbial biomass carbon was observed under homegarden agroforestry practices from upper soil (505.36 + 12.45 mg kg -1) and woodlot agroforestry practices (surface: 464.37 + 9.19 mg kg - 1) whereas the lowest value was registered from the subsurface of the parkland agroforestry practices (153.10 + 46.44 mg kg -1). Regarding microbial biomass quotient result, the higher percentage was recorded under the woodlot agroforestry practices from upper soil layer (1.48%) and then homegarden agroforestry practices (surface = 1.41%). The homegarden and woodlot agroforestry practices types were suitable agroforestry practices types for soil biodiversity conservation (arbuscular mycorrihizal fungi and soil macrofauna), improves soil microbial biomass carbon, glomalin related soil protein, soil aggregate stability, and soil aggregate stability class distribution. Hence, these AFPs are the suggestible land management practices which should be advocated.