Calculating pH from EC and SAR values in salinity models and SAR from soil and bore water pH and EC data.

Abstract

Currently used soil salinity models do not contain a mechanism for including exchangeable sodium effects on soil pH. A method is needed that allows pH calculation from the sodium adsorption ratio (SAR) or exchangeable sodium percentage (ESP) and electrical conductivity (EC) data. This study developed a simple method for calculating saturated soil paste and aqueous solution pH from SAR (or ESP) and EC data and compared the results with measured values from a number of soils and subsurface waters. The equation pH -A+{B*(SAR) 1/2 /(1+CEC)I estimated soil pH from EC and SAR or ESP values. When rewritten as: SAR or ESP = l(pH-A)(1+C'EC)/13} 2 , the SAR or ESP was estimated from pH and EC data. By using shallow bore (well) water and soil extract data from the Murray Basin, values were determined for the scalar terms A, B and C. These values differed among subsurface water and soil types, however, the range of each scalar was reasonably small. It was found that a range of at least 2 . 5 pH units in the calibration data was necessary to obtain reliable regression between predicted and measured pH and SAR or ESP values. When these conditions were met, the predicted results were satisfactory. These relationships provide a method for pH calculation in soil salinity models which takes into account soil EC and sodium effects. They also provide a rapid field method to estimate SAR or ESP from easily obtainable EC and pH data. Further research is needed to define the factors that determine the values of A, B and C.

Coefficients for estimating SAR from soil pH and EC data and calculating pH from SAR and EC values in salinity models

“…Neither of the above assumptions are realistic for sodic or saline-sodic soil reclamation models or for modeling sodium degradation of non-salt-affected soils under many conditions. A useful pH calculation method was developed that includes ESP or SAR and EC change effects on soil pH in sodic and salinesodic soil models (Robbins and Meyer 1990) and does not require the presence of lime. This was accomplished by rewriting Eq.…”

“…1. The development of these equations is detailed by Robbins and Meyer (1990). The original soils used to develop and test Eqs.…”

“…It also showed that the coefficient values differed with depth and that surface soil data had to be separated from subsoil data to get reasonable pH and SAR or ESP prediction precision (Robbins and Meyer 1990).…”

“…Using data from highly weathered, sodic, Australian soils, a model was developed for estimating ESP or SAR from pH and EC data (Robbins and Meyer 1990). The model has the form…”

Effects of Magnetic Water Irrigation on the Growth, N Uptake and Antioxidant Enzyme Activities of Cotton Seedlings

“…Soil salinization is a widespread phenomenon in arid and semi-arid areas and occurs primarily due to the inappropriate agricultural practices, such as flooding irrigation [1] and excessive fertilization [2]. According to the Food and Agriculture Organization (FAO), in 2000, saline areas have exceeded 950 million hectares at the global scale, accounting for approximately 10% of global land area [3].…”