Abstract
Recent research findings imply that the slope aspect has a great impact on soil genesis and soil microclimate. The microclimate has a significant effect on the soil geobiochemical processes taking place in the soil. However, the slope aspect impact on soil properties has not been yet studied well in Ethiopia, particularly in the northern highlands. This research was initiated to link selected soil physicochemical properties with slope aspects under different land use practices. The research was conducted in Gumara-Maksegnit watershed located at the upper Lake Tana basin, Ethiopia. Four slope aspects, eastward (Ew), northward (Nw), southward (Sw), and westward (Ww), and three land use types at each slope aspect, cropland (Cl), forest land (Fl), and grazing land (Gl), were considered. In total, 36 undisturbed soil samples for bulk density and 36 disturbed soil samples for selected soil properties were collected. Soil particle size (texture), bulk density, electrical conductivity (EC), soil pH, available phosphorus (av. P), available potassium (av. K), total nitrogen (TN), and soil organic carbon (SOC) were analyzed. The resulting analyses showed no significant variation (p<0.05) across both slope aspects and/or land use types for soil pH and EC, whereas the slope aspect showed a significant effect (p<0.05) on SOC, TN, av. K, and av. P. The highest significant (p<0.05) mean value of SOC was observed in the Ww (3.04%) followed by Nw (2.52%) but SOC was not significant (p<0.05) between Sw and Ew. While the highest av. K (1233.2 centimole/kilogram) and av. phosphorus (35.76 ppm) were observed in Nw slope aspect, the highest TN was in the Ww slope aspect (0.24%). The significant effect (p<0.05) of land uses can be summarized as Fl > Gl > Cl for SOC and TN. A strong positive correlation was observed between SOC and TN (R2 = 0.997) and av. K and av. P (R2 = 0.58) at p<0.05. Generally, the slope aspect, land use types, and their interaction had a significant effect on soil physicochemical properties.
Highlights
Ethiopian highland areas are characterized by high rainfall and have continually practiced diversified cultivation with rapid land use changes [1]
Gumara-Maksegnit watershed lies in the critical part of the Lake Tana basin which is the largest lake in Ethiopia under Megechi Catchment. is catchment drains into the Gumara-Maksegnit River, which drifts to Lake Tana (Figure 1). e biophysical processes in this catchment have a direct impact on the ecosystem of the Lake Tana. e Gumara-Maksegnit watershed is found in north Gondar zone of Gondar Zuria district with the geographical location which ranges between 12°23′53′′ to 12°30′49′′N and 37°33′39′′ to 37°37′14′′E. e watershed is located approximately 45 km southwest of Gondar town
Descriptive Analysis of Selected Soil Properties. e descriptive analyses of the results revealed that there was a numerical difference among the selected physicochemical soil properties across the slope aspect and land use types, while soil organic carbon and bulk density showed similar patterns (Figure 2)
Summary
Ethiopian highland areas are characterized by high rainfall and have continually practiced diversified cultivation with rapid land use changes [1]. Improper agricultural practices such as overgrazing, continuous tillage, poor soil, and water conservation practices and soil acidity affect the soil ecology and properties [2]. The slope gradient combined with traditional agriculture has aggravated soil fertility depletion, soil acidity, and soil organic matter depilation [4]. Deviations due to topographic aspects brought diverse microclimates, causing differences in faunal abundance and diversity, soil moisture, temperature, and organic matter to affect soil fertility and soil quality [6]. Hydrological and solar energy systems of mountainous landscapes vary according to slope aspect, which leads to the variance in composition and distribution patterns of vegetation and soil biological properties [7]
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