Evaluation of Various Extractants for Available Soil Sulfur
- R. G. Hoeft,
- L. M. Walsh and
- D. R. Keeney
The S status of 49 Wisconsin soils was evaluated in field studies using alfalfa (Medicago sativa) as the test crop. The effectiveness of six soil S extractants for predicting yield and S uptake response to applied S were evaluated by means of correlation analyses. The best extractant, considering all dependent variables and the S range, mean and standard deviation for each procedure, was 2N HOAc containing 500 ppm P as Ca(H2PO4)2 · H2O [Ca(H2PO4)2-HOAc]. The correlation between extractable S and response to applied S was not improved by inclusion of percent organic matter, percent sand, or subsoil SO4-S in the regression equation. However, inclusion of soil pH with extractable S did significantly improve the prediction of S response.
The best equation for prediction of yield response to applied S in the field was: Yield response (metric tons/ha) = 50.81 − 7.22 pH − 8.19 S + 1.171 (pH × S) + 0.167 (S)2 − 0.00341 (pH × S)2 where S is the ppm of S extracted with Ca-(H2PO4)2-HOAc. Significant response to applied S would be expected on soils having a calculated yield response of 0.40 metric tons/ha or greater when extractable S is between 6 and 10 ppm S. Soils testing less than 6 ppm would be expected to respond and those testing greater than 10 ppm S would not be expected to respond to application of S, regardless of the calculated response value. Use of the regression equation and the limits of 6 and 10 ppm S resulted in correct prediction of S response at 77.6% of the field sites.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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