ESTIMATING AVAILABLE WATER-HOLDING CAPACITY OF WESTERN NIGERIAN SOILS FROM SOIL TEXTURE AND BULK DENSITY, USING CORE AND SIEVED SAMPLES

Using core and sieved soil at −1/3 and −15 bar matric potentials, we determined water retention on a number of western Nigerian soils and related it by predictive equations to soil textural separates and bulk density (BD). We obtained the soils from forested and cultivated croplands over 12 sites selected in the sedimentary and basement complex regions to give a representative range of soil textures and bulk densities. Water retention at −1/3 bar by core was estimated by functions of sand and BD with a minimum standard error (SE) of 1.70% and for sieved soil by functions of silt and clay (SE of 1.36%). Clay content alone predicts the −15 bar water (SE of 0.70% and r2 = 0.93). Available water-storage capacity (AWSC), expressed on a gravimetric basis by the core method, can be predicted with an SE of 1.54% by the regression equation AWSC = 14.01 + 0.03 (silt x clay) – 8.78(BD) (r2 = 0.83), which is related to sieved soil AWSC by the following equation with SE of 1.00% (r2 = 0.92): AWSCcore = 14.04 + 1.07(AWSCsieved) – 9.46(BD) + 0.14(sand).