Impact of Elevation Change on the Physicochemical Properties of Forest Soil in South Omo Zone, Southern Ethiopia

Abstract

The assessment of the distribution of soil physicochemical properties provides basic information for our understanding of the soils to grow crops and sustain forests and grasslands. The changes in soil physicochemical properties along elevational gradients were studied in a less accessible Sida Forest, southern Ethiopia. Hence, the present study was conducted to assess the distribution of soil physicochemical properties along the elevational gradients and to evaluate the fertility status of the soil. Data on soil physicochemical properties were collected from five points (four from each corner and one from the center) of the main plot. A pit of 20 cm × 20 cm was dug at a depth of 0–30 cm and a kilogram of composite soil samples was brought to the Wolkite Soil Testing Laboratory for physicochemical analysis. The results revealed that the physicochemical properties of the collected soil samples show a significant correlation with elevation changes. Sand had a significantly negative correlation and variation with elevation; it decreases as elevation increases with the rate of correlation (r = −0.44 ∗ ∗ , P ≤ 0.001 ). However, silt had a nonsignificantly positive (r = 0.20, P < 0.079 ) correlation to the elevation, while clay had a significantly positive correlation to elevation, and it increases as elevation increases with the rate of correlation coefficient (r = 0.40 ∗ ∗ , P ≤ 0.001 ). Soil OC, OM, TN, CEC, and exchangeable Mg2+ had significant positive correlation to the elevation; they increase as elevation increases with the rate of correlation coefficient (r = 0.42 ∗ ∗ , P ≤ 0.001 ), (r = 0.41 ∗ ∗ , P ≤ 0.001 ), (r = 0.44 ∗ ∗ , P ≤ 0.001 ), (r = 0.34 ∗ ∗ , P < 0.002 ), and (r = 0.27 ∗ , P < 0.014 ), respectively. While BD, pH, EC, Av. P, exchangeable Ca2+, and exchangeable K+ had a nonsignificant negative correlation to the elevation, they decrease as elevation increases with the rate of correlation (r = −0.70 ∗ ∗ , P < 0.134 ), (r = −0.20, P < 0.075 ), (r = −0.05, P < 0.683 ), (r = −0.04, P < 0.701 ), (r = −0.04, P < 0.693 ), and (r = −0.053, P < 0.693 ), respectively. This study attempted to provide information on the impact of elevation on soil’s physicochemical properties. Given that, the soil’s physicochemical properties exhibit variation with elevation changes.

Relationship of selected properties of Cambisols to altitude and forest ecosystems of four vegetation grades

“…The N t content detected in the soils of the forest ecosystems studied by us indicates a positive relationship with altitude, or FVG ( R2 = 0.811). A significant correlation ( p ≤ 0.05) of total topsoil nitrogen with altitude was also found by Kidanemariam et al [ 64 ] in the Tsegede highlands of the Tigray region of northern Ethiopia and Hailemariam et al [ 48 ] in a less accessible Sida Forest, southern Ethiopia ( r = 0.44; p < 0.001). Malik and Haq [ 65 ] report that at altitudes of 900–2600 m in a part of the western Himalayas, only the N content showed a significant positive correlation with altitude ( r = 0.924, p ˂0.05), while all the other soil nutrients showed a non-significant negative correlation with it.…”

“…The Cambisols located at altitudes of 257 and 265 m in the 2nd beech-oak FVG had significantly lower humus contents (36–45 mg g −1 ), while the extremely acidic Dystric Cambisols located at altitudes 760 and 950 m in the 5th fir-beech FVG had significantly higher humus contents (109–112 mg g −1 ). Hailemariam et al [ 48 ] in a less accessible Sida Forest, southern Ethiopia also found significant positive correlations between the soil organic carbon ( r = 0.42; p < 0.001) and organic matter ( r = 0.41; p < 0.001) with altitude. Based on the characteristics of 12,742 soil samples taken over from forest management plans from 1982 to 2014, Enescu et al [ 73 ] report that the organic matter content in the Eutric and Dystric Cambisols of Romania is affected by altitude and tree age, especially on shaded and partially shaded slope aspects.…”

“…The tightness of the dependence of the linear regression of clay on altitude and FVGs was low ( R2 < 10 %). On the other hand, in the less accessible Sida forest of southern Ethiopia, Hailemariam et al [ 48 ] found a significant positive correlation of clay with altitude ( r = 0.40; p < 0.001). Sims and Nielsen [ 49 ] reported that clay content apparently has much less effect on organic C accumulation in cool Montana soils than in warmer soils of the southern Great Plains.…”