Steady-State Prediction of Sodium Adsorption Ratio (SAR) in Drainage Water Based on Irrigation Water Quality in a Lysimetric Study

摘要

Different types of equations have been proposed to predict the drainage water sodium adsorption ration (SAR; SAR(dw)). These equations are verified here against the data of a lysimetric study. Cylindrical lysimeters with diameter of 40 and height of 180 cm were filled with a sandy loam soil and irrigated weekly with natural water. A set of 30 drainage water analyses was used for which measurements of irrigation and drainage water quality and quantities were done. Then a set of 116 water analyses throughout Iran was used to adjust some of available equations for local conditions. Simple correlations between irrigation water SAR and that of drainage water yielded to poor regression coefficient (R-2 = 0.108), whereas steady-state assumption could fairly predict SAR(dw) (R-2 = 0.802), which is comparable with more complex methods recently proposed. The WatSuit model predicted values of the mean SAR(dw) based on average leaching fraction (LF) that were very close to the measured mean of drainage water SAR.