Use of Soil-profile Sulfate Data for Predicting Crop Response to Sulfur
1987
Hue, N. V. | Cope, J. T.
Sulfur deficiencies in early growth stages do not always result in final yield reduction in many crops. This suggests a greater contribution of subsoil sulfate (SO₄) and/or of S mineralization later in the season to the S requirements of plants. The subsoil SO₄ contribution should be assessed in order to develop a method that can reliably predict crop response to S. A greenhouse experiment was conducted with various combinations of topsoil (0-20 cm layer) and subsoil (20-60 cm layer) materials from a Hartsells series (Typic Hapludult) where crop response to S had been observed, and a Benndale series (Typic Paleudult) where there was no response to S in field experiments. By determining soil SO₄ depletion in each layer by crops of grain sorghum (Sorghum bicolor L. Moench.), it was extimated that plants derived approximately 0.55 of their S need from the surface 0 to 20 cm, and the remaining 0.45 from the subsoil. Subsequently, a weighted concentration of soil SO₄ for the entire profile was calculated; and values of 13.8 mg S kg⁻¹ for extractable SO₄ and 0.25 mM for soil-solution SO₄ were the minimum concentrations above which no crop response to S is expected. The use of weighted means of soil-profile SO₄ data correctly predicted yield responses to S of soybeans (Glycine max L. Merr.), corn (Zea Mays L.), and sorghum in a field experiment, which were previously unexplained based on SO₄ concentrations of the surface soil.
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