BRIEF PRE-IRRIGATION AND POST-IRRIGATION SPRINKLING WITH FRESH-WATER REDUCES FOLIAR SALT UPTAKE IN MAIZE AND BARLEY SPRINKLER IRRIGATED WITH SALINE WATER

Brief pre- and post-irrigation sprinkling treatments using freshwater were tested to determine if these practices could reduce the uptake of salts through leaves when saline water is used to sprinkler irrigate crops. Maize and barley were sprinkler irrigated 2 to 3 times per week for 30 min with saline water (4.2 dS m(-1), 30 mmol L(-1) NaCl and 2. 8 mmoles L(-1) CaCl2 for maize and 9.6 dS m(-1), 47 mmoles L(-1) NaCl and 23.5 mmoles L(-1) CaCl2 for barley) in separate experiments with p lants grown in pots outdoors. The soil surface of all pots was covered to prevent salinization of the soil by the sprinkling water. One half of the sprinkled plants was grown in nonsaline soil to study the effe cts of pre-wetting and post-washing when ion uptake was primarily thro ugh leaves. The other half of the sprinkled plants was grown in soil s alinized by drip irrigation, in order to evaluate the effects of pre-w etting and post-washing when Na+ and Cl- uptake was through both leave s and roots. Post-washing with freshwater (5 min) reduced the leaf sap concentrations of Cl- in saline-sprinkled plants from 56 to 43 mmol L (-1) in maize and from 358 to 225 mmol L(-1) in barley (averages for p lants grown in nonsaline and saline soil). Ndt concentrations in leaf sap were reduced from 93 to 65 mmoles L(-1) (maize) and from 177 to 97 mmoles L(-1) (barley) by the post-washing. Pre-wetting had a small ef fect on ion uptake through leaves, the only significant reduction in s easonal means being in leaf Na+ concentrations for plants grown in non saline soil. Pre-wetting and post-washing, when combined, reduced leaf Cl- concentrations to levels similar to those of nonsprinkled plants grown in saline soil; however, Na+ concentrations in leaves remained 3 .5 times (maize) and 1.5 times (barley) higher than those of nonsprink led plants. When pre-wetting and post-washing were not applied, sprink led barley plants grown in saline soil had grain yields which were 58% lower than nonsprinkled plants grown in saline soil, but the reductio n in grain yield was only 17% when the freshwater treatments were give n. We conclude that a brief period of post-washing with freshwater is essential when saline water is employed in sprinkler irrigation. By co mparison, the benefits from pre-wetting were small in these experiment s.