Plant-Available Sulfur as Measured by Soil-Solution Sulfate and Phosphate-Extractable Sulfate in a Ultisol1
- N. V. Hue,
- Fred Adams and
- C. E. Evans2
Because S deficiency in young small grain plants is not uncommon on limed, sandy Ultisols, a method predicting S requirement for the plants is needed. A greenhouse study was conducted to determine the effects of S at different pH levels on wheat (Triticum aestivum L.) growth, S concentration of plant tissue, soil-solution sulfate (SO42−), and phosphate [Ca(H2PO4)2]-extractable SO42−. A Benndale loamy sand surface soil (coarse-loamy, siliceous, thermic Typic Palendult) was treated with three lime rates (0,5.6, and 8.1 mmol kg−1) and four gypsum rates (0,10, 20, and 40 mg S kg−1 for the first two lime levels and 0,8,16, and 32 mg S kg−1 for the highest lime level). Plant tissue samples were taken 5,9,13, and 17 weeks after planting, and soil samples were taken at planting and 9 and 17 weeks later. There was a yield response to S at each harvest, regardless of soil pH. Yield and S uptake were both highly correlated with soil-solution SO42− concentration and with Ca(H4PC4)2-extractable SO42−. As a result of plant uptake, soil-solution 42− decreased after each harvest, with the greatest redaction occurring at the highest lime rate. Sulfur mineralization from organic matter provided significant 42−" to plants in low-S treatments, and some added SO42− became nonextractable at high S rates. Minimum SO42− concentrations for maximum wheat growth was 0.25 mM in soil solution and 6.0 mg S kg−1 in Ca(H2PO4)2 extract. Minimum S concentration in plant tissue for maximum dry matter yield was 1.6 g kg−1.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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