Effect of Exchangeable Sodium on the Hydraulic Conductivity of a Soil as Measured by Two Procedures under Field Conditions

Effect of exchangeable sodium on hydraulic conductivity under field conditions was investigated in field plots of a highly sodic soil (Aquic Natrustalfs) which had been differentially treated with gypsum 5 years earlier. The hydraulic conductivity (K) was evaluated by measuring hydraulic gradients and water fluxes during on evaporation phase and also during a drainage phase [when evaporation was prevented and it could be adequately described in all cases by the relationship of the type K=aeβθ. The effect of high exchangeable sodium in reducing hydraulic conductivity was greater in the wet than in the moist range. Thus, at 40 per cent water content by volume, the hydraulic conductivity decreased 11-fold as the ESP increased from 4 to 38, whereas the corresponding decrease was only 3-fold at 10 per cent water content. It was further observed that as the ESP increased from 4 to 16, K at 40 per cent water content decreased by only 4-fold, whereas K decreased 10-fold when the ESP increased from 4 to 23.