Exclosures backed up with community-based soil and water conservation practices increased soil organic carbon stock and microbial biomass carbon distribution, in the northern highlands of Ethiopia

Abstract Background Land degradation is a treat for natural resources in Tigray high lands of northern Ethiopia, where 30–50 percent of the soil productive capacity has been lost in the past 500 years. Restoration and management of degraded lands improve soil health through enhancing soil organic carbon (SOC) stock and microbial biomass carbon (MBC). The knowledge on SOC and MBC concentration and distribution is essential to refine soil management, thereby restoring the ecosystem. This paper quantified the effect of decades old community-based soil and water conservation (SWC) measures, mainly stone terraces, exclosure with and without stone terraces, and non-conserved communal grazing lands on the distribution of MBC and SOC stock. Methods Soil sample collection was carried out using systematic sampling design. Transects parallel to each other and to the slope of the landscape were established. In each transect, three landscape positions (i.e., upper, middle, and foot slope) were formed. Composite soil samples were taken from four corners and center of 10 m × 10 m plot of each slope positions under the different SWC measures. Analysis of variance was used to determine the difference in SOC and MBC using SAS 9.2. Results Total soil organic carbon concentration was significantly higher in exclosures as compared to terraces and non-conserved grazing lands. The highest mean value of SOC stock (29 Mg C ha−1) was recorded 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 recorded in non-conserved communal grazing lands. Exclosures with terraces improved SOC stock by 64%, followed by exclosures without terraces by 37%, while terraces improved the SOC stock by 25% compared to non-conserved open communal grazing lands in the last 20 years. The upper (0–15 cm) soil depth had significantly (P < 0.05) higher (24 Mg C ha−1) SOC stock than the lower (15–30 cm) soil depth (20 Mg C ha−1). Microbial biomass carbon was the highest (640 mg kg−1 soil) in exclosures without terraces, followed by exclosures with terraces, (570 mg kg−1 soil), terraces (440 mg kg−1 soil), and non-conserved communal grazing lands (370 mg kg−1 soil). Conclusion Exclosures supported with terraces improved and restored the SOC stock and microbial biomass carbon of degraded free grazing lands in the highlands.