Reassessing irrigation water quality guidelines for sodicity hazard

Current irrigation water quality guidelines for sodicity hazard, in use since the 1980s, are based on assessments of salinity (Electrical conductivity, EC) and sodicity (Sodium Adsorption Ratio, SAR), where SAR considers the positive effects of calcium (Ca) and magnesium (Mg) against the adverse effects of sodium (Na) on soil permeability. Recent research and practice, however, have provided ample evidence for negative effects of both potassium (K) and Mg on soil physical properties in addition to Na. This paper (1) discusses a proposed irrigation water quality parameter which generalizes SAR by including the Potassium Adsorption Ratio (PAR) along with two adjustable numerical coefficients for the K and Mg concentrations to reflect their role as dispersive cations; (2) discusses the tradeoffs from including K and the complex effects of Mg in irrigation water quality assessment; (3) analyzes water quality using the new parameter for 600 water samples from irrigated regions around the world; and (4) proposes revised irrigation water quality guidelines for assessing soil permeability hazard, a generalization of sodicity hazard. Revising current irrigation water quality guidelines in this way will help practitioners assess the suitability of a given water more accurately and will guide fit-for-purpose options and associated management strategies to ensure the sustainability of irrigated agriculture as the use of marginal-quality waters increases to meet the challenge of freshwater scarcity.