Comparison of Seven SO4-S Extraction Methods for Analysis by Turbidimetry or ICP Spectrometry
2015
Cihacek, L. J. | Yellajosula, G. | Jacobson, K. A. | Swenson, L.
Soil sulfur (S) analyses for fertilizer recommendations in the northern Great Plains often do not reflect crop S requirements. Seven SO ₄-S extraction methods with S determination by either turbidometry or inductively coupled plasma emission spectroscopy including Ca(H ₂PO ₄) ₂ and KH ₂PO ₄ (both containing 500 ug/l P), 0.25 M KCl (40 ºC) and 0.25 M KCl (room temperature), H ₂O, DTPA, and Mehlich 3 extractants. Three horizon depths of three soils from a previous field study were used for these comparisons. Average standard deviations for turbidometric determinations were 4.3 times greater than ICP determinations. With turbidometry, S values were H ₂O > KH ₂PO ₄ > Ca(H ₂PO ₄) ₂ > KCl (40 ºC) = KCl, while with ICP, the values were Mehlich 3 > KCl (40 ºC) = KCl > DTPA (diethylenetriaminepentaacetic acid) > KH ₂PO ₄ > H ₂O > Ca(H ₂PO ₄) ₂. Extraction with KCl at room temperature with ICP determination appears to show promise, but further method evaluation is necessary before it can be recommended as a SO ₄-S test method.
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