Development of functions to predict soil hydraulic properties that account for solution sodicity and salinity

Abstract

Saturated soil hydraulic conductivity (Ksat) and the soil water characteristic curve have been predicted from soil texture, bulk density, and other soil physical properties. These previous functions do not account for soil clay mineralogy or soil solution composition. The objectives of this study were to: (1) analyze the performance of previously developed pedotransfer functions (PTFs) on saline and sodic soils, (2) predict hydraulic properties of saline and sodic soils with a range of clay mineralogy, and (3) develop PTFs that account for clay mineralogy and solution composition. Most PTFs do not perform well on soils with smectitic clay mineralogy and usually over-estimate Ksat and under-estimate soil water characteristic on smectite clay dominant soils. Accounting for soil cation exchange capacity (CEC) as an indicator of soil clay types and solution composition improved the prediction of Ksat which had a geometric root mean squared error of 3.28 cm day−1 compared to 6.04 cm day−1 for the best performing PTF from the literature. A PTF we developed to predict soil water characteristic curve was able to predict soil water characteristic curve with a root mean squared error of 0.032 g g−1 compared to 0.082 g g−1 for the best performing previously published PTF. The PTFs developed in this study improved prediction of soil hydraulic properties on salt affected soils by using soil CEC to account for soil clay behavior and responsiveness to the soil solution composition. The PTFs reported here can easily be used to predict the Ksat and the soil water characteristic curve of soils in response to changes in irrigation water quality.