DETERMINATION OF PHYSICO -CHEMICAL AND HYDRAULIC CHARACTERISTICS OF SOILS UNDER DIFFERENT AGRICULTURAL LAND USES IN AKURE, NIGERIA

Abstract

This study investigated the physico-chemical and hydraulics characteristics of soil under long-term land use in Akure, southwestern Nigeria. The three agricultural land uses under study are cassava cropland, cocoa plantation, and biochar amended soil. Random sampling pattern of 6 sampling points per sample location (20 m apart) were carried out and undisturbed soil samples were collected in soil at depths up to 30 cm (i.e. 0 – 10, 10 – 20, and 20 – 30 cm) in each location from the different land use types making a total of 54 samples in all. Soil physical properties such as bulk density (BD), total porosity (TP), soil water holding capacity (WHC), and particle size distribution and chemical properties such as soil organic matter (SOM), soil organic carbon (SOC), cation exchange capacity (CEC), phosphorus (P) and total nitrogen (N); soil strength and hydraulic conductivity were determined in order to evaluate the effects of land use types. Handheld mini disk infiltrometer at a steady- state flow of – 2cm water suction rate was used to determine the unsaturated hydraulic conductivity, water and ethanol sorptivity at each land use site. The sand, silt and clay fractions were not significantly affected by land uses, soil depths but was significantly affected by the interaction of land uses and soil depths (p ≤ 0.001). Land use significantly affected bulk density, total porosity, water holding capacity, soil organic matter/carbon, total nitrogen and cation exchange capacity of the land use types (p ≤ 0.001, p ≤ 0.01 and p ≤ 0.05). Soil water sorptivity follows the order: cassava cropland (204.60 cm h-1/2) > biochar amended soil (147.00 cm h-1/2) > cocoa plantation (50.80 cm h-1/2). Mean unsaturated hydraulic conductivity values showed an increasing trend from the cocoa plantation to cassava cropland and biochar amended soil in the order: 1.64 cm h-1 ± 1.22, 5.75 cm h-1 ± 1.38, 8.19 cm h-1 ± 0.57. Unsaturated hydraulic conductivity (K) was significantly different among the various land use types (p < 0.001). Difference in water repellency among cassava cropland, cocoa plantation and biochar amended soil were not statistically significant (p > 0.05). The mean water repellency index decreased in order: cocoa plantation > biochar amended soil > cassava cropland with values 1.83 ± 1.21 > 1.65 ± 0.79 > 0.84 ± 0.13, respectively. The hydrophobicity of soils was higher in soils with high organic matter content (cocoa plantation soils) and biochar amended soils, whereas the reverse was the case in croplands. The difference in the unsaturated hydraulic conductivity among the land use types might be due to the combination of land use management and differences in microbial activities affecting soil texture and structure. Results also show that soil properties such as organic matter content, bulk density, water holding capacity, and aggregate sizes influence the infiltration characteristics of soils in the study areas. This research establishes facts about the hydraulic and water repellency properties of soils, provide a better understanding of the soil characteristics and water management under different land uses, and recommends useful methods by which soil could be improved towards the development of suitable agricultural management systems