Assessment of soil response to exchangeable sodium percentage by consistence and water retention properties

Abstract

The use of low-quality water for irrigation is expected to keep increasing worldwide, which increases the risk of soil degradation. The response of soil to irrigation waters with excessive sodium depends on the soil clay behavior. Soil physical properties that can distinguish smectitic soils from non-smectitic soils could identify soils that are sensitive to exchangeable sodium. This study explores the use of Atterberg limits, coefficient of linear extensibility (COLE) and soil water retention as possible properties to determine if a soil is sensitive to exchangeable sodium. Soils used were synthetic soils prepared from mixtures of silt and clay minerals, and six natural soils. Atterberg limits, COLE and soil water retention was measured at ESP values of 0, 50 and 100% on these soils. Multiple linear regression functions were developed to predict soil liquid limit, plasticity index, COLE, and soil water retention at −336 cm H2O. The liquid limit, and COLE increased as the amount of sodium-saturated smectite increased in the synthetic soils. The liquid limit, COLE and water retention at matric potentials greater than −336 cm of H2O increased on smectite clay dominant soils when elevated ESP was combined with low salinity. The liquid limit increased from 49 to 67 on average and −336 H2O water content increased from 38 to 70% on average between 0 and 100% ESP treatments on the four smectitic soils. On a kaolinitic soil liquid limit decreased from 56.1 to 51.8 and −336 H2O water content increased from 33.7 to 35.9% between the ESP 0 and 100% treatment. Liquid limit increased from 188 to 679 and COLE increased from 0.47 to 1.19 mm mm−1 between calcium smectite (fullers earth) and sodium smectite (Wyoming bentonite), whereas liquid limit decreased from 56 to 39 and COLE decreased from 0.195 to 0.104 mm mm−1 between calcium and sodium saturated kaolinite. Plasticity index increased by 75% between the ESP 0 and ESP 100 treatments on the smectitic soils, whereas there was a 260% increase in plasticity index between fullers earth and bentonite. The root mean squared error that liquid limit could be predicted with was 3.3 plastic limit was 2.4, COLE was 0.036 mm mm−1, and 1/3rd bar water content was 2.2 × 10−3 g g−1. Smectitic soils had increases in soil swelling related properties, whereas non-smectitic clay soils had no changes in swelling related properties from ESP. Liquid limit and water retention at water potentials of −1/10th and −1/3rd bar were the properties that best distinguished soils that respond to ESP from soils that do not respond to ESP. Soil consistence properties and water retention can determine soils that contain smectite clay which is the clay mineral that is most sensitive to soil ESP.