Submitted to: Journal of Plant Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/2/2004
Publication Date: 5/10/2005
Citation: Wang, D., Grieve, C.M., Suarez, D.L. 2005. Composition of irrigation water salinity affects growth characteristics and uptake of selenium and salt ions by soybean. Journal of Plant Nutrition. 28:1073-1088. Interpretive Summary: Soybeans are grown as a high-protein, high-energy crop for both humans and livestock. Soy proteins are used in infant formulas, food supplements, and a variety of foods as a functional ingredient. Fortification of certain soy proteins with selenium, an essential mineral and important antioxidant, improves the nutritive quality of the soy products. Selenium (Se) from seleno-proteins is more available to consumers than from inorganic sources. However, the range for optimum Se nutrition is very narrow. Toxicities and deficiencies may occur outside this range. A greenhouse experiment was conducted to determine the effects saline irrigation waters differing in mineral ion composition have on soybean growth and ion accumulation in leaves and seed. Two different irrigation compositions were used: (1) chloride-dominated waters, and (2) sodium-sulfate dominated waters prepared to simulate typical saline drainage effluents present in the San Joaquin Valley of California. For each water composition, six levels of salinity were imposed and 1 ppm Se was added to all treatments. Growth was not significantly affected by the type of irrigation water used. Se was higher in both leaves and stems of plants irrigated with chloride-based waters compared with those grown with the sulfate-dominated waters. Depending upon the ultimate consumer, Se-enriched soybean seed could provide adequate Se nutrition directly or could be mixed with Se-deficient seed or other rations from to give the desired Se-formulation.
Technical 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 soybean (Glycine max L. Merr.) cultivar 'Manokin'. Plants were grown in sand cultures and irrigated with isoosmotic solutions containing (i) Cl- as the dominant anion, or (ii) a mixture of salts containing equal molar amounts of SO42- and Cl-. Six treatments of each salinity type were imposed. Electrical conductivities of the irrigation waters ranged from 2.1 to 13.0 dS/m. Se (1 mg/L, 12.7 µM) was added to all irrigation waters as Na2SeO4. Regardless of salinity type, soybean plants were generally taller in 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 in the intermediate salinity levels (5.0 and 9.2 dS/m), 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 in the sulfate salinity treatment. Plant uptake and accumulation of salt ions (Ca2+, Mg2+, Na+, Cl-), K+, total-P, and total-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 in the chloride salinity. Se concentration in leaves and seeds was about 4 mg/kg at final harvest when irrigated with the sulfate-based saline waters. In the chloride salinity, Se was found to be about three times as much in the leaves and five times as much in the seeds. In conclusion, different solution concentrations of SO42- 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.