ORIGIN OF THE EFFECT OF PH ON THE SATURATED HYDRAULIC CONDUCTIVITY OFNON-SODIC SOILS

The effect of pH on the saturated hydraulic conductivity (K) of repack ed columns of two non-sodic soils (Healaugh and Fagaga soils) was exam ined. The K value was greater for the Fagaga soil than for the Healaug h soil which is attributed to the difference in the amount of free iro n oxides between the soils. The K values reached a maximum when the pH was close to the point of zero net charge (PZNC) (3.7 and 4.8 for the Healaugh and the Fagaga soil, respectively) and decreased on either s ide of these pH values. The effect of pH on K was related to its effec t on surface charge. As the pH of variable-charge soils approaches the PZNC, the net surface charge decreases resulting in flocculation and maintenance of a high K. Conversely, as the pH deviates from the PZNC, the net surface charge increases, resulting in dispersion and a decre ase in K. There was a negative relationship between the amount of disp ersed clay and the K values, suggesting that clay dispersion and the r esulting clogging of pores decreases K in these soils.