The Impact of Magnesium Versus Calcium On Infiltration.

Scarcity of fresh water in arid regions means results in an increasing need to use lower quality water for irrigation. Lower quality waters include waters that are more saline, more sodic, contain greater concentrations of alkalinity and thus greater pH as well as greater proportions of Mg relative to Ca then compared to fresh waters. The adverse effects of SAR on saturated hydraulic conductivity in laboratory columns are well documented, and there is limited information on both long term effects on infiltration as well as information on the combined effects of pH and SAR. There is also information on the effects of Mg versus Ca on infiltration. In this study we examine the infiltration of waters with an EC of 1 dS/m and variable SAR, comparing the effects of Ca versus Mg at the same SAR examining both irrigation only and irrigation rain cycles using a rain simulator. The study was conducted for one year and included wetting and drying cycles. We observed, as expected, that the infiltration was reduced using Mg versus Ca at equivalent SAR values. The results are related to 2 effects, soil stability of Ca versus Mg systems, and the lower preference of Mg for Na on the exchange sites, as compared to Ca for Na. We developed a response function relating infiltration to SAR as well as to the final measured ESP. These results will be useful to development of guidelines for use of low quality waters for irrigation.