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Soil Science Society of America Journal Abstract -

Comparison of the Amounts and Forms of Sulfur in Soil Organic Matter Fractions after 65 Years of Cultivation1


This article in SSSAJ

  1. Vol. 44 No. 1, p. 70-75
    Received: May 29, 1979
    Accepted: Sept 18, 1979

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  1. J. R. Bettany,
  2. S. Saggar and
  3. J. W. B. Stewart2



Large differences in organic matter contents of a Udic Haploboroll soil were observed in the A horizons of adjacent cultivated (for 65 years) and permanent pasture sites. Relatively lower net losses of S (38%) comared to C (44%) and N (49%) and narrower C/N/S ratios indicated that S is more resistant to mineralization during cultivation processes than C and N. Organic S concentrations were lower in all 6 fractions obtained from a 0.1M NaOH-0.1M Na4P2O7 (pH 13.0) extraction separation but differences were noted in absolute amounts and relative proportions of C, N and S lost from specific fractions. Three fractions, conventional humic acid (HA-A), clay associated humic acid (HA-B) and humin (<2 µm), accounted for 80% of the total S difference. In contrast, the fulvic acid (FA-A) fraction which had narrower C/N/S ratios, contained more HI-reducible S and was thought to be more labile than other fractions, only contributed 14% of the total S loss.

It was postulated that the breakdown and oxidation of HA-A, HA-B and humin <2-µm fractions during mineralization would liberate low molecular weight S compounds which would temporarily accumulate in FA-A fractions thereby accounting for a small net decrease in total S and a high percentage of HI-reducible S in this fraction in the cultivated soil.

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