EFFECT OF SOIL AND WATER CONSERVATION PRACTICES ON THE DYNAMICS OF SOIL BIOTA AND BIOMASS CARBON IN NORTHERN HIGHLANDS OF ETHIOPIA

Abstract

Soil and water conservation practices in Tigray, northern highlands of Ethiopia are given special emphasis for the restoration of degraded lands. However, information on the effect of SWC practices on the dynamics of soil biota is limited. This study was conducted with the objective of evaluating the effect of two decades long community-based soil and water conservation (CBSWC) practices, viz, stone terraces, exclosure with and without stone terraces which were evaluated against non-conserved communal grazing lands on soil organic carbon (SOC) stock, microbial biomass carbon (MBC), arbuscular mycorrhiza fungi (AMF), soil glomalin and soil macroinvertebrates (SMIs) abundance and diversity. Soil samples were collected from each CBSWC systematically using transects based on slope positions. The selected soil properties were measured using standard procedures. Besides, SMI abundance and diversity were computed. Analysis of variance (ANOVA) was used to analyze data using SAS 9.2. The results revealed that the highest SOC stock (29Mg C ha-1) was found in exclosures with terraces followed by exclosures without terraces (24 Mg C ha-1), and terraces (21 Mg C ha-1), while the lowest (16 Mg C ha-1) was found in non-conserved communal grazing lands. Microbial biomass carbon was the highest (i.e., 640 mg kg-1soil) in exclosures without terraces followed by exclosures with terraces (570 mg kg-1soil); terraces (440 mg kg-1soil) and non-conserved communal grazing lands (370 mg kg-1soil). In this study five major AMF genera including Glomus, Acaulospora, Gigaspora, Scuttelospora and Entrphospora were identified. Glomus, the abundant genus accounted for 52% of the total spore density followed by Acaulospora 18%. Exclosures had the highest spore density (60%) followed by stone terraces (23%), while open non-conserved communal grazing lands had the lowest (17%). Total root colonization along the CBSWC measures ranged from 48.6% in open non-conserved communal grazing lands to 68.7% in exclosure with terrace. In addition three forms of AMF root colonization namely hyphae, arbuscules and vesicles were identified. All forms AMF root colonizations were higher in the exclosures followed by terraces. Terraces had significantly higher (P < 0.05) total AMF root colonization than open non-conserved communal grazing lands. Easily extractable glomalin (EEG) and total glomalin (TG) were significantly (P < 0.05) higher in exclosures as compared to terraces and non-conserved grazing lands. Exclosures had significantly (P < 0.05) higher percent of water stable aggregate (WSA) than non-conserved grazing lands. Mean weight diameter (MWD) were also significantly (P < 0.05) higher in exclosures. Soil macroinvertebrate diversity was higher (1.21) in the exclosure supported with terraces followed by exclosures without terraces (1.01) and the lowest (0.9) was observed for the non-conserved communal grazing lands. Soil macro invertebrate diversity was also significantly (P <0.05) higher (1.26) in wet than dry (0.70) season. The highest (41%) Sorensen similarity index among SMIs was found between exclosure with terraces and exclosures without terraces during the wet season. The lowest (20%) Sorensen similarity index was found between terraces and exclosures with terraces in dry season. Soil macroinvertebrate abundance was higher in upper (0-10 cm) than lower (10-20 and 20-30 cm) soil depths. It is concluded that building of terraces and exclosures on the degraded highlands improved soil organic carbon stock, microbial biomass carbon, arbuscular xix mycorrhiza, Glomalin and soil macroinvertebrate abundance and diversity. Thus, the study recommends scaling out community based soil and water conservation practices as they are proven local technologies so as to regenerate degraded ecosystems sustainably.