Effect of Landscape Positions on Soil Properties in an Agricultural Land A Transect Study in the Main Rift Valley Area of Ethiopia

Abstract

This study addressed the effects of landscape positions on morphological, physicochemical properties of soils in
the Main Rift Valley of Ethiopia. Three landscape positions: upper, middle and lower; and three profile horizons:
A, B and buried Ab were considered along a transect line. Nine soil profiles; three in each landscape position,
were opened, described and samples collected from each of the observed diagnostic horizon and analyzed. The
average thickness of the A- horizon was 34 cm in the upper, 10 cm in the middle and 50 cm in the lower landscape
positions. Gravels and high sand fractions (average, 41.4%) dominated the B-horizons, indicating the low rate of
weathering. The clay fractions and soil bulk density (p<0.001), available water capacity (AWC) (p=0.050), soil
organic carbon (SOC) and total N (p= 0.004 and 0.025, respectively), Available P (p=0.004), Exchangeable Ca2+
(p=0.019) and CEC (p=0.010) varied significantly with horizons. Landscape positions also influenced the textural
fractions of clay, bulk density, AWC, SOC, total N, available P, exchangeable Ca2+ and CEC. However, the SOC
concentration across the profiles were low due to the combination of lower inputs because of less biomass return
on harvested land, increased aeration by tillage and crop residue collection for fire. The low available P might be
due to the high P-fixation behavior of andosols. Continuous cultivation without appropriate soil management
practices has resulted in more complex and non-systematic patterns of soil nutrient distribution. Thus, landscape
level management practices are required to replenish soil nutrients for sustainable agriculture.