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SOIL HYDRAULIC PROPERTIES OF A CHROMIC LUVISOL IN KATUMANI, KENYA

Background: Soil hydraulic parameters in non-saturated conditions are crucial for explaining soil water dynamics in the field. It is therefore necessary to understand the link between soil water potential and hydraulic conductivity in the soil in order to estimate plant available water and hence simulate its movement within the soils. However, measurement of such hydraulic properties in the field and laboratory is somehow difficult, laborious and costly. Objective: To determine soil hydraulic properties of Ferro-chromic Luvisols in Katumani using the RETC code based on pedo-transfer functions; % sand, silt, clay and soil bulk density. Methodology: Undisturbed soil samples were collected from a profile pit at 0-15, 16-30, 31-45 and 46-60 cm depths using core rings for bulk densities and texture determination. Soil water retention curves and saturated hydraulic conductivities (Ksat) were estimated for all the samples using standard suction apparatus and the constant head method, respectively. The air entry suction (α) and pore size distribution (n) were generated using the RETC code. Results: The permanent wilting point and field capacity were at 0.081, 0.102, 0.107 and 0.121 and 0.188, 0.225, 0.241, 0.262 m3m-3 H2O, whilst its soil water diffusivity ranged from a low of 6.39, 6.94, 9.03 to a high of 12.5 cm2min-1 in the 0-15, 16-30, 31-45 and 46-60 cm depth, respectively. Ksat values from RETC code ranged from 29 - 48 cm day-1, while the total and readily available water within the soil profile were 330.4 and 214.7 mm H2O, respectively. Implication: The air entry value (α) and pore size distribution (n) implied an almost even distribution from the top and subsequent horizons. The soils ‘field capacity was achieved at pF 2.0 whilst PWP was arbitrary indicated at pF 4.2 reducing the time it takes to calculate irrigation cycles based on the amount of water available to the crops. Conclusion: The data indicates that pedo-transfer functions; especially high bulk densities negatively impact on soil hydraulics conductivity.