Validity of Light Transmittance to Predict Soil Hydraulic Conductivity in Salt-Affected Soils

Abstract

LAY dispersion and flocculation are very common processes in ……...salt-affected soils and have a direct impact on the movement of water and dissolved ions. This study was aimed to make use of light transmittance (% T) through soil suspension as a monitor and to reflect the intensity of dispersed clay particles as it relates to hydraulic conductivity (K), and percent of clay dispersion. To achieve this aim, two soils with varied clay contents, were collected from Beheira (S1) and Gharbia (S2) Governorates in north of Nile Delta, Egypt, and treated with sodium (Na), calcium (Ca), and magnesium (Mg) chlorides to obtain combinations of sodium adsorption ratio (SAR) and electrical conductivity (EC) treatments. Measurements of K and T might be affected by exchangeable cations and correlated negatively with SAR. Results showed that values of T were decreased continually (tendency to clay dispersion), that might be a good indicator for changes of K. Relations between T, K and SAR indicated high clay dispersion and low K as SAR increased. The empirical equations derived from both K and T measurements may introduce a new approach to predict K, taking into consideration the clay content, EC and SAR of the soils. Promising results were obtained when these equations were subjected to evaluation, using 15 various soil samples with high correlation coefficient of determined versus estimated K (R 2 = 98 %). Calculation of dispersion (%) for SAR-EC treatments, using T and standard clay curve (% T versus clay content) showed that soil aggregates are not always stabilizing by an increase of sodium ions and it is not needed to reach complete clay dispersion to clog the conducting pores and loss of water permeability. Dispersion percent decreased within a given SAR as EC increased due to the adverse effect of salinity (tendency to accumulation) on sodicity.