SATURATED HYDRAULIC CONDUCTIVITY IN RELATION TO PHYSICAL-PROPERTIES OF SOILS IN THE NSUKKA PLAINS, SOUTHEASTERN NIGERIA

Information on the most important physical properties that influence t he saturated hydraulic conductivity (K-s) of soils is useful in modell ing water and solute movement during ponded infiltration and in estima ting both temporal and spatial variation in K-s. In this study the K-s of 18 sites with different land use histories on a watershed in the N sukka plains of southeastern Nigeria was determined and related to sel ected soil physical properties. The purpose was to develop a simple st atistical model for estimating K-s from more easily determined propert ies and to evaluate how close K-s is to Philip's fitted soil water tra nsmissivity (A) and measured steady (final) infiltration rate (I-c) (P hilip, 1957). The saturated hydraulic conductivity correlated positive ly with total porosity (r(2) = 0.182) and macroporosity (P-e), defined as pores with equivalent radius > 15 mu m (r(2) = 0.635) and negative ly with bulk density (r(2) = 0.533). Mesoporosity (i.e., pores with an equivalent radius of 1.5-15 mu m) and microporosity (i.e., pores with an equivalent radius of 0.1-1.5 mu m) also correlated negatively with K-s with respective r(2) values of 0.275 and 0.100. The best fit mode l relating K-s to the soil physical properties was K-s = 0.07e(0.08(Pe )) (r(2) = 0.946). With this model the threshold P-e value below which there is a drastic reduction in K, lies between 15 and 20%. Using an independent data set to validate this model, predicted and measured K- s values were generally in good agreement. This model is valid for P-e values between 1.3 and 41.2% which is the common range in these uplan d soils. The values of I-c, K-s and A were statistically different (P less than or equal to 0.001) and varied in the order I-c> K-s>A, showi ng that the assumption that at long infiltration times these values ar e all approximately equal does not hold for these soils.