Plant‐Available Sulfur as Measured by Soil‐Solution Sulfate and Phosphate‐Extractable Sulfate in a Ultisol1

Abstract

AbstractBecause 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 aestivumL.) 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 Paleudult) 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−1for the first two lime levels and 0,8,16, and 32 mg S kg−1for 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 mMin soil solution and 6.0 mg S kg−1in Ca(H2PO4)2extract. Minimum S concentration in plant tissue for maximum dry matter yield was 1.6 g kg−1.