Composition of Irrigation Water Salinity Affects Growth Characteristics and Uptake of Selenium and Salt Ions by Soybean

A greenhouse study was conducted to determine the effects of irrigation waters differing in salt composition on growth characteristics, salt ion and selenium (Se) accumulation, and distribution in plant components of the soybean (Glycine max L. Merr.) cultivar “Manokin.” Plants were grown in sand cultures and irrigated with isoosmotic solutions containing (1) Cl− as the dominant anion, or (2) a mixture of salts containing equal molar amounts of SO2− 4 and Cl −. Six treatments of each salinity type were imposed. Electrical conductivities of the irrigation waters ranged from 2.1 to 13.0 dSm−1. Selenium (1 mg · L−1, 12.7 μM) was added to all irrigation waters as Na2SeO4. Regardless of salinity type, soybean plants were generally taller under the low-salinity treatments in early vegetative stages of growth. Towards the end of vegetative stages and until final harvest, higher values of plant height, leaf area, and shoot dry weight were found at the intermediate salinity levels (5.0 and 9.2 dS m−1), and higher salinity in general led to increased soybean leaf chlorophyll on a unit-area basis. Shoot-to-root ratios decreased with increasing chloride salinity, while the ratios remained nearly constant under the sulfate salinity treatment. Plant uptake and accumulation of salt ions (Ca2+, Mg2+, Na+, Cl−), K+, total phosphorus (p), and total sulfur (s) were generally not related to the type of salinity, except total S, where higher concentrations were found in leaves, stems, and roots in the sulfate than under the chloride salinity treatment. Selenium concentration in leaves and seeds was about 4 mg kg−1 at final harvest when irrigated with the sulfate-based saline waters. Under the chloride salinity treatment, Se level was found to be about three times higher in leaves and five times higher in seeds. In conclusion, different solution concentrations of SO2− 4 and Cl − had no significant effect on soybean biophysical growth parameters or ion distribution. Whereas shoot-to-root ratios Received 23 December 2003; accepted 2 June 2004. Address correspondence to D. Wang, Department of Soil, Water, and Climate, University of Minnesota, St. Paul, MN 55708, USA. Email: [email protected]