Land use effect on soil quality and its implication to soil carbon storage in Aleta Chuko, Ethiopia

Soil quality index (SQI) is a useful tool to identify soil productivity status and design management strategies. Land use (LU) and management conditions can affect the physico-chemical qualities of the soil which in turn influences the carbon storage ability of the soil. However, the effects of LU on soil quality and associated carbon storage are not well understood in the Aleta Chuko. Three transect lines were drawn based on spatial analogue design covering three LU types, 4 plots for each land use from individual transect, 12 plots per LU, a total of 36 plots, and then 108 soil samples (0–30 cm depth) were taken in three diagonal pits within 20 × 20 m. 19 soil physico-chemical and biological properties were evaluated for SQI, and 12 soil quality indicators were selected using principal component analysis. The results showed that soil physico-chemical and biological characteristics were better under Coffee-enset based agroforestry (CEA) than Chat mono-cropping (CM) and Eucalyptus woodlot (EW). CEA showed significantly higher macro aggregate ≥ 5 mm, steady infiltration rate, Av. P, Av. K, Ex. K, total N, CEC and MBC, but no significant difference was observed between CM and EW in these variables (p < 0.05). SQI of CEA, CM and EW were 0.61, 0.53 and 0.50, respectively. The higher SQI in CEA was due to high MBC(586.3 μg g⁻¹ soil), litterfall, SOM (4.7 %) and low bulk density (BD, 0.87 g cm⁻³). Total soil organic carbon was significantly higher in CEA (35.2) > CM (24.2) > EW (19.4) g kg⁻¹ soil and the same is true for Mg²⁺ CEA (4.9), CM (3.9) and EW (2.7) meq 100 g⁻¹ (p < 0.05). Multiple regression analysis on five (BD, CEC, MBC, Ex. Ca and macro aggregates) soil quality determinant variables predicting SOC showed that these variables have a significant effect on SOC (p < 0.001). Specifically, BD and MBC were significant negatively and positively predicting variables of SOC, respectively (p < 0.001). This study suggests that LU practice and management variances over similar biophysical environments resulted in variations in soil physico-chemical, biological properties and the subsequent difference in SQI which in turn determine SOC storage capacity of the soil. Long-term effects of Eucalyptus and CM on soils should be a concern for degradation, although their short-term economic benefits are attractive.