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

Abstract

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 SO₄ ^{2 −} 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 μ M) 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 (Ca^{2 +}, Mg^{2 +}, 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 SO₄ ^{2 −} and Cl⁻ had no significant effect on soybean biophysical growth parameters or ion distribution. Whereas shoot-to-root ratios decreased with increasing chloride salinity, high-sulfate salinity reduced Se uptake by “Manokin” soybean.

Keywords:

• soybean
• selenium uptake
• chloride salinity
• sulfate salinity
• ion inhibition
• ion partitioning
• shoot-to-root ratio
• sand culture

ACKNOWLEDGMENTS

The authors are indebted to Donald A. Layfield for mineral ion analyses, to James Wood for selenium analyses, to Jim Poss and Terry Donovan for leaf area and SPAD meter measurements, and to Phyllis Nash for statistical analyses.

Notes

Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the University of Minnesota or the U.S. Department of Agriculture.

^*Different letters indicate significant difference (P = 0.05) for the same ion among all plant parts and salinity levels.

^*Different letters indicate significant difference (P = 0.05) among all plant parts and salinity levels.