Organic matter dynamics and aggregation in soils under rain forest and pastures of increasing age in the eastern Amazon Basin

Organic matter dynamics and aggregation in soils under rain forest and pastures of increasing age... In the eastern Amazon basin, four neighbouring clayey Oxisols with similar particle-size distributions were selected, one under rain forest and three under pasture for 7, 12 and 17 years, respectively. These soils were sampled at depth intervals of 0.1 m down to 1 m. Although no clear effect of pasture establishment on aggregate stability was assessed, significant negative effects of cattle trampling on porosity and water retention and of vegetation change on clay water-dispersion were observed in the organic-rich horizons (0–0.40 m layers). Indirect evidence of a great change of the nature of organic materials was also suggested, particularly with (i) an increase in both negative surface charges and clay dispersibility, attributed to an increase in organic functional groups, and (ii) a decrease in clay fabric porosity, attributed to an increase in the hydrophilic-hydrophobic balance on organic surfaces (short-range adhesion forces during drying processes). Studies of soil organic matter (SOM) changes along this forest-to-pasture sequence were based on total C and 13 C measurements, which allowed to calculate the distribution of C derived from forest (Cdff) and from pasture (Cdfp) throughout the profiles. The distribution of C and 13 C in the whole soil, in water-stable (WSA), in not stable (NWSA) aggregates, and in particle fractions, was compared. Young organic residues derived from pasture were trapped in WSA, from where they were released by dispersion. After 17 years, the decrease in forest-derived SOM and the input of about 25% of pasture-derived SOM were suggested to be more effective on clay dispersability than on aggregate stability. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geoderma Elsevier

Organic matter dynamics and aggregation in soils under rain forest and pastures of increasing age in the eastern Amazon Basin

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Publisher
Elsevier
Copyright
Copyright © 1997 Elsevier Ltd
ISSN
0016-7061
eISSN
1872-6259
D.O.I.
10.1016/S0016-7061(96)00105-X
Publisher site
See Article on Publisher Site

Abstract

In the eastern Amazon basin, four neighbouring clayey Oxisols with similar particle-size distributions were selected, one under rain forest and three under pasture for 7, 12 and 17 years, respectively. These soils were sampled at depth intervals of 0.1 m down to 1 m. Although no clear effect of pasture establishment on aggregate stability was assessed, significant negative effects of cattle trampling on porosity and water retention and of vegetation change on clay water-dispersion were observed in the organic-rich horizons (0–0.40 m layers). Indirect evidence of a great change of the nature of organic materials was also suggested, particularly with (i) an increase in both negative surface charges and clay dispersibility, attributed to an increase in organic functional groups, and (ii) a decrease in clay fabric porosity, attributed to an increase in the hydrophilic-hydrophobic balance on organic surfaces (short-range adhesion forces during drying processes). Studies of soil organic matter (SOM) changes along this forest-to-pasture sequence were based on total C and 13 C measurements, which allowed to calculate the distribution of C derived from forest (Cdff) and from pasture (Cdfp) throughout the profiles. The distribution of C and 13 C in the whole soil, in water-stable (WSA), in not stable (NWSA) aggregates, and in particle fractions, was compared. Young organic residues derived from pasture were trapped in WSA, from where they were released by dispersion. After 17 years, the decrease in forest-derived SOM and the input of about 25% of pasture-derived SOM were suggested to be more effective on clay dispersability than on aggregate stability.

Journal

GeodermaElsevier

Published: Mar 1, 1997

References

  • Total and young organic matter distributions in aggregates of silty cultivated soils
    Puget, P.; Chenu, C.; Balesdent, J.

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