Effect of Saline Irrigation Waters on Soil Manganese Leaching and Bioavailability to Sugar Beet

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Abstract
Use of saline water for irrigation has shown considerable promise. However, its effect on the solubility and bioavailability of native soil nutrients is not well understood. This study was conducted to evaluate the extent of the salt‐induced Mn solubility and phytotoxicity to sugar beet [Beta vulgaris (L.) USH 11] under a soil‐plant‐leachate system. Sugar beet grown in the glasshouse on four diverse California soils was irrigated with either deionized water or 22.5 and 45.0 mol m−3 NaCl‐CaCl2 solution. Saline irrigation waters significantly (P < 0.001) increased (27 to 97%) the Mn concentration ([Mn]) and total Mn accumulation (48 to 130%) in sugar beet tops in all soils. The [Mn] in the soil solution leachate increased significantly with net increases of 55.3, 35.5, and 2.6 mg Mn kg−1 in Maymen, Aiken‐Tehama, and Aiken‐ElDorado soil, respectively, for the highest salinity, but only traces of Mn were detected in leachate of a high pH (8.23) Mojave soil. Diethylenetriamine pentaacetic acid (DTPA)‐extractable soil Mn significantly increased with salinity levels in irrigation waters in Maymen (92%), Aiken‐ElDorado (68%), and Mojave (47%) soils, but decreased (37%) in Aiken‐Tehama soil of low pH (5.10) and low C (3.60 g kg−1). The multiple regression analyses produced R2 = 0.864*** (P < 0.001) when shoot [Mn] was regressed on ECe, soil solution [Mn], soil pH, and DTPA‐extractable soil Mn. Since sugar beet tops contained in excess of 1000 mg Mn kg−1 top tissue, it was concluded that salt‐induced Mn accumulation under saline irrigation can be potentially toxic.