Abstract
Infiltration is the key to soil water conservation and management. Distribution of soil physical properties within profile and infiltration behaviour is relevant to erosion studies or occurrence. Hence a research was conducted within the Teaching and Research Farm of the University of Ibadan, Nigeria, the main objectives were to assess profile distribution of physical properties of the soil, quantify infiltration behaviour of the soil, fit the data into Philip and Kostiakov infiltration models, and relate the infiltration behaviour to soil physical properties. The surface texture was sandy loam and sub-surface layers varied from sandy Loam, sandy clay loam, sandy loam and clay. Mean values for gravel were 392.56, 345.00 and 250.00 g kg-1 and bulk densities were; 1.65, 1.75 and 1.82 g cm-3 for upper, middle and foot slope, respectively. The high bulk densities obtained indicate high runoff, low infiltration and proneness of the soil to erosion and difficulty of plants meeting their water needs. Clay fraction increased down the profile from upper slope to foot slope. Saturated hydraulic conductivity was highest at the upper slope (2.40 cm/hr) and least at the foot slope (0.29 cm/hr) for the same soil layer. Initial one minute and cumulative infiltration were; (9.00, 571.00 cm), (1.80, 108.0 cm) and (4.70, 369.60 cm) for upper, middle and foot slope respectively. Infiltration along the toposequence was lowest on the middle slope. The coefficient of correlation (r) value of Philip and Kostiakov infiltration models ranges between 0.89 and 0.99, indicating their suitability for infiltration rate prediction. Infiltration consistently negatively correlated with bulk density. Absorptivity parameter of the soil correlated with bulk density. Absorptivity parameter of the soil correlated positively with hydraulic conductivity, coarse sand, fine sand and gravel content. Sorptivity (s) correlated negatively with hydraulic conductivity, coarse sand, and gravel content of the soil. The index of soil stability (alpha) correlated positively with soil hydraulic conductivity, coarse sand and gravel content of soil but negatively with fine sand, silt and clay content. Use of vetiver grass strip and grass mulch to slow down runoff velocity, break slope length, increase microbial and earthworms’ activities is recommended for the study location and toposequence as this will reduce soil bulk density, increase soil porosity, infiltration and availability of water within the rooting zone.
