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

摘要

Information on the most important physical properties that influence the saturated hydraulic conductivity (K-s) of soils is useful in modelling water and solute movement during ponded infiltration and in estimating 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 Nsukka plains of southeastern Nigeria was determined and related to selected soil physical properties. The purpose was to develop a simple statistical model for estimating K-s from more easily determined properties and to evaluate how close K-s is to Philip's fitted soil water transmissivity (A) and measured steady (final) infiltration rate (I-c) (Philip, 1957). The saturated hydraulic conductivity correlated positively 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 negatively 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 model 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 upland 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, showing that the assumption that at long infiltration times these values are all approximately equal does not hold for these soils.