Strength and hydraulics characteristics variations within a tropical Alfisol in Southwestern Nigeria under different land use management

This study investigated the hydraulics and strength characteristics of an Alfisol under long-term land use in Akure, southwestern Nigeria. The three agricultural land uses under study are Cropland, Grazing land, and Oil palm plantation. Hydraulic conductivity tests were randomly conducted at 60 sampling points per location (10 m apart), to make a total of 180 samples from the three land uses, while the unconfined compressive strength (quf) and vane shear strength measurement were conducted in the laboratory and insitu, respectively on soil at depths up to 45 cm (i.e. 0-15, 15 - 30, and 30 - 45 cm). The hydraulic conductivity and soil water sorptivity were determined using mini disk infiltrometer at a steady-state flow of - 0.5, - 1 and - 2 cm water suction rates. Land use and land cover change significantly affected the hydraulic and mechanical properties of the soil (p ≤ 0.001, p ≤ 0.01 and p ≤ 0.05). The hydraulic conductivity value showed an increasing trend from the grazing land to cropland and oil palm plantation in the order: grazing land (4.72 cm h−1) < cropland (10.80 cm h−1) < oil palm plantation (13.21 cm h−1). Grazing land recorded the highest mean soil water sorptivity value, while oil palm plantation had the least value. Grazing land had the highest average quf and shear strength among the land use types at depths 0-15 cm, 15-30 cm and 30-45 cm of soil. Depth - wise consideration showed that in all the land uses, unconfined compression strength (quf), shear strength and vane shear strength significantly increased with depth. Soil properties such as organic matter content, bulk density, and aggregate sizes influence the infiltration and strength characteristics of soils of the study area. Land uses influenced the hydraulic properties and strength characteristics of agricultural soils and therefore, assessment of changes in soil properties under land use types should be conducted periodically to effectively monitor the soil status over time. This will guide decisions on measures adoptable to ensure the sustainability of soil structure and texture for optimum crop productivity.