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Sodium Hypochlorite Methods for Extracting Microelements Associated with Soil Organic Matter¹

ABSTRACT

Since hydrogen peroxide (H₂O₂) and sodium pyrophosphate (Na₄P₂O₇) dissolve portions of the manganese and iron oxide fractions, respectively, sodium hypochlorite (NaOCl) was studied as an alternate organic fraction extractant for microelements. Six top soils were extracted for Mn, Cu, Fe, and Zn in a boiling water bath with NaOCl alone (5.3%), NaOCl plus 0.005M DTPA (diethylenetriaminepentaacetic acid), or NaOCl with DTPA added during the last few minutes of extraction. Other variahles were time (15 or 30 min) and one or two extractions. The effects of each method on the Mn oxide and amorphous Fe oxide fractions were evaluated. A second extraction increased the amounts of metal ions extracted. Increasing extraction time solubilized additional Mn and Zn but the effect was less for Cu and Fe. NaOCl + DTPA extraction values for the metals were not different from those for NaOCl alone. Adding DTPA during the last few minutes of extraction greatly increased the amounts of extractable metals. When DTPA was added at the end, metal values for the Mn oxide and amorphous Fe oxide fractions were significantly less than for the other two treatments. Two 30-min extractions with NaOCl alone are recommended. Since it appeared to extract microelements from the oxide fractions under these conditions, DTPA should not be added.

¹ Contribution from the Dep. of Agronomy, Univ. of Georgia, Georgia Station, Experiment, GA 30212. Presented before Div. S-2 of the Soil Sci. Soc. of Am., Anaheim, Calif., 1 Dec. 1982.

² Associate Professor of Agronomy, Georgia Station, Experiment, GA 30212.

Received for publication November 18, 1982. Accepted for publication January 31, 1983.