Savanna land use and its effect on soil characteristics in southern Ethiopia

We tested soil characteristics and nutrient availability linked to settlement age, grazing pressure and fire regime in southern Ethiopia. Settlement categories included: non-settlement (no evidence of settlement), recent (<15 years) and old (>40 years). Grazing pressure was represented by enclosures vs. grazed areas, while fire regime denoted by burned vs. unburned sites. Soil properties and vegetation characteristics were analyzed for different treatments. Our results showed that higher sand content could reduce soil pH values with increased leaching. Low soil pH could also occur due to the high rate of organic matter decomposition and uptake of cations by plants. We recorded higher nitrogen (N) and phosphorus (P) contents with N = 0.16 +/- 0.01% and P = 21.10 +/- 1.28 mg kg(-1) in recent compared to old settlement. Electrical conductance (EC) was positively influenced by soil pH. We observed significantly higher EC under increased grazing. Higher soil pH, N, organic carbon (OC) and cation exchange capacity (CEC) were recorded in recent compared to non-settlement. Fire greatly improved soil condition, while heavy grazing reduced grass biomass. We suggest the need for appropriate land management and soil conservation by minimizing impacts of cultivation on soil characteristics. We also propose the reintroduction of fire to restore rangeland biodiversity. (C) 2012 Elsevier Ltd. All rights reserved.