Infiltration as Influenced by Irrigation Water Quality

Abstract After 19 months of irrigation with waters of different quality, columns of Heimdal loam cropped to alfalfa had infiltration rates that were correlated better with irrigation water sodicity and salinity than with soil surface (0–76 mm) or column average (0–530 mm) exchangeable sodium and soil salinity. Two sets of irrigation water parameters were tested: (i) total cation concentration ( C c ) in mol c m ‐a (meq liter −1 ) and sodium adsorption ratio (SAR c ) of the irrigation water in equilibrium with solid phase CaCO 3 at a P CO2 of 0.07% based on ion activities corrected for ion pairing; and, (ii) total cation concentration of the irrigation water as prepared and the adjusted sodium adsorption ratio based on the calculated pH of the water in equilibrium with CaCO 3 . On the basis of multiple linear regression analyses, the best correlation was obtained with the lime‐equilibrated water parameters ( R 2 = 0.87). The corresponding relationship between infiltration rate ( I ) in mm hour −1 and the chemical parameters was I = 6.80 − 1.10 SAR c + 0.79 C c . Cation concentration greatly affected infiltration rates even at low SAR levels (2<SAR<5). Apparently, the mechanical action of the applied water greatly enhances the effects of exchangeable sodium and soil solution concentration on swelling and dispersion at the soil surface which, in turn, has a large effect on infiltration rates.