Canadian Forest Service Publications

A comparison of soil extraction procedures for 31P NMR spectroscopy. 1996. Cade-Menun, B.J.; Preston, C.M Soil Science 161(11): 770-785.

Year: 1996

Issued by: Pacific Forestry Centre

Catalog ID: 4709

Language: English

Availability: PDF (download), PDF (request by e-mail)

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The effect of extractants on phosphorus determination by 31P NMR spectroscopy was examined using five forest floor samples. The extractants used were: 0.25 M NaOH, 1:6 soil to Chelex in water, 1:6 soil to Chelex in 0.25 M NaOH, and a 1:1 mix of 0.5 M NaOH and 0.1 M EDTA. The broadest peaks were produced by the NaOH + EDTA extraction. However, NaOH + EDTA extracts contained the highest percentage of total phosphorus and the greatest diversity of P forms. These extracts were the only ones to show peaks for polyphosphates. Metals analysis indicated that NaOH + EDTA maintained Mn in solution, which seemed to be responsible for the line broadening. The sharpest peaks, with the best separation, were produced with Chelex + NaOH, and these were improved further by increasing the pH with NaOH prior to NMR analysis. Chelex + NaOH extracted 23 to 35% of the total soil P, Chelex in water extracted 10 to 30%, NaOH alone extracted 22 to 34%, and NaOH + EDTA extracted 71 to 90%.

The work suggests that, because the extractant used will affect the P forms, care must be taken when interpreting studies of P cycling in soils using 31P NMR spectroscopy and when comparing studies using different extractants.