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This article in SSSAJ

  1. Vol. 44 No. 1, p. 70-75
     
    Received: May 29, 1979
    Published: Jan, 1980


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doi:10.2136/sssaj1980.03615995004400010016x

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

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

Abstract

Abstract

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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