Soil Science

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Author: search.filters.author.KENEA FEYISA JIRATASubject: search.filters.subject.Borana rangeland

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    THE DYNAMICS OF LAND USE MANAGEMENT ON CARBON SEQUESTRATION, SOIL PROPERTIES AND VEGETATION ATTRIBUTES IN BORANA, SOUTHERN ETHIOPIA
    (Hawassa University College of Agriculture, 2018) KENEA FEYISA JIRATA
    The Borana rangelands of southern Ethiopia have been extensively used as grazing lands by pastoralists for millennia.However, there has been a dramatic shift from prime grazingland to cultivation, left unused because of bush encroachment, and highly degraded leading to different land use/land cover types in the region. Therefore, this thesis work was designed to study the dynamics of land use management on carbon sequestration, soil properties and vegetation attributes by considering the roles played by enclosure management, different land use systems, the aboveground biomass of woody species, and long-term ban of prescribed range fire. This study was conducted in Yabello district of Borana, southern Ethiopia during the period from June-August 2013. A paired-site design approach was used in this study, where sampling plots (30 m x 30m each) with nested’ subplots for field data collection on soil and vegetation layers were establishedin a systematic random sampling techniquealomga 500 m long transect line in each adjacent experimental site.Using enclosures versus the adjacent open-grazed as control, our results showed that the SOC and TN contents and stocks increased in enclosures as compared to the adjacent open-grazed rangelands, although the differences were not significant (P > 0.05) and varied along the age sequence and soil depths.Overall, totalmean SOC stocks of 39.6 ± 3.5 Mg ha−1 in the younger (< 20 years old), 40.8 ± 3.4 Mg ha −1 in the medium (20–30 years old ) and and 51.0 ± 4.4 Mg ha −1 in older (> 30 years old) enclosures age categories, whereas in the adjacent open-grazed areas the values ranged from 34.4 ± 2.5 to 47.9 ± 5.1 Mg ha−1in 0-30 cm. The herbaceous biomass was significantly (P<0.05) higher inside enclosures (115.4 gm m-2) than that of the adjacent open-grazed rangeland areas (43.6 gm m -2).The study in this thesis showed that the Borana rangelands had undergone substantial changes in land use/land cover during the last 37 years. Our results also showed that mean SOC stocks (0-30 cm) in woodland was 55.94±3.41 Mg ha-1,while for enclosure, grazing xvii and cultivated lands the values were 50.03±3.03, 45.79±4.00 and 38.10±2.39 Mg ha -1 , respectively. Additionally, woodland had the highest (7.52±0.43 Mg ha-1), while cultivated land had the lowest (5.58±0.35 Mg ha-1) total nitrogen stock. The potential changes of SOC and TN stocks also showed both gain and loss based on the present measurements and historical land use change. The developed species specific and mixed species allometric equation models for majorities of the investigated woody species ithat related the total above-ground, stem and branches biomass components well fit to the measured dendrometric variablesas as indicated by their adjusted coefficient of determinations and highly significant (adj.R² > 0.80; P < 0.001). The study on long-term of ban of fire on carbon stocks in soil and woody biomass, and TN stock across the two landscape site showe that relatively higher SOC and TN contents and stocks as well as herbaceous biomass carbon in burned than unburned areas, whereas more accumulation of woody biomass carbon was recorded in the unburned sites (40 years of fire exclusion).Overall, this study will contribute to the existing knowledge gaps in terms of the potential of SOC and TN stocks related to different rangeland management practices as well as anestimate of the above-ground woody biomass in arid and semi-arid ecosystems of southern Ethiopia. However, it is suggested further study including other variables such as climatic factors, seasonality and inherent soil properties across wider landscapes, which may have confounding effects on the dynamics of carbon sequestration other than land management practices for the sustainable use of the savanna rangelands of southern Ethiopia.