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Performance of exclosure in restoring soil fertility: A case of Gubalafto district in North Wello Zone, northern highlands of Ethiopia

Damene, Shimeles, Tamene, Lulseged, Vlek, Paul L.G.
Catena 2013 v.101 pp. 136-142
agroecological zones, analysis of variance, biodiversity, biomass production, canopy, carbon, good agricultural practices, grazing, ground vegetation, highlands, land degradation, landscape position, landscapes, microclimate, mineralization, nitrogen content, organic matter, physicochemical properties, planning, soil fertility, soil resources, soil sampling, vegetation cover, vegetation types, water conservation, Ethiopia
Inappropriate agricultural practices and conversion of marginal land to cultivation and grazing have led to severe land degradation in the Ethiopian highlands. Consequently, the government has invested substantial resources in soil and water conservation (SWC). One of such interventions was exclosure, which was aimed restoring biodiversity, biomass and soil fertility. The aim of this study was to analyze the impact of exclosures on soil fertility restoration and examine its variability across age, agro-ecology and landscape position. The study was conducted in the Gubalafto district of North Wello Zone, northern Ethiopian highlands. Vegetation cover was estimated and soil samples were collected from three age categories (open sites, 10- and 27-year-old exclosures), two agro-ecological zones (mild and cool) and in three landscape positions (lower, mid and upper). The samples were analyzed for selected soil physico-chemical properties using standard laboratory procedures. The results were statistically tested using analysis of variance (ANOVA). Vegetation ground and canopy cover increased with exclosure age. The soils of the exclosures showed significantly higher organic carbon (9g/kg) and total nitrogen content (1.2g/kg p≤0.06 at α=0.05) than the open sites. However, no statistical significant difference was observed between the 10- and 27-year-old exclosures, indicating that the restoration rate decreased with increasing exclosure age. This could be related to the low quantity and quality of the biomass, which influenced organic matter input and mineralization. Exclosures in the mild zone showed significantly higher soil fertility restoration than those in the cool zone. The differences between the two zones could be attributed to the effect of micro-climate on biomass production, vegetation types and organic matter mineralization. The soil physico-chemical properties neither had significant differences nor followed a regular trend across the landscape positions. The non-significant soil fertility restoration variation across the landscape positions could be attributed to complementary effect of structural SWC measures. Therefore, exclosure implementation and utilization planning should consider soil fertility restoration variation with age, agro-ecology and management conditions of the respective exclosure.