Preprints
https://doi.org/10.5194/soil-2020-98
https://doi.org/10.5194/soil-2020-98

  26 Feb 2021

26 Feb 2021

Review status: a revised version of this preprint is currently under review for the journal SOIL.

Aluminous clay and pedogenic Fe oxides modulate aggregation and related carbon contents in soils of the humid tropics

Maximilian Kirsten1, Robert Mikutta2, Didas N. Kimaro3, Karl-Heinz Feger1, and Karsten Kalbitz1 Maximilian Kirsten et al.
  • 1Technische Universität Dresden, Institute of Soil Science and Site Ecology, Tharandt, Germany
  • 2Martin-Luther-Universität Halle-Wittenberg, Soil Science and Soil Protection, Halle/Saale Germany
  • 3Mwenge Catholic University, Directorate of Research Innovations and Consultancy, Moshi, Tanzania

Abstract. Aggregation affects a wide range of physical and biogeochemical soil properties with positive feedbacks on soil carbon storage. For weathered tropical soils, aluminous clays (kaolinite and gibbsite) and pedogenic Fe (oxyhydr)oxides (goethite and hematite; termed Fe oxides) have been suggested as important building units for aggregates. However, as both secondary aluminosilicates and Fe oxides are part of the clay-sized fraction it is hard to separate, how certain mineral phases modulate aggregation, and what consequences this has for organic carbon (OC) persistence after land-use change. We selected topsoils with unique mineralogical compositions in the East Usambara Mountains of Tanzania under forest and cropland. Soils are varying in contents of aluminous clay and Fe oxides. Across the mineralogical combinations, we determined the aggregate size distribution, aggregate stability, OC contents of aggregate size fractions as well as changes in aggregation and OC contents under forest and cropland land use. We found the soil aggregation patterns (high level of macroaggregation and aggregate stability) more similar than different among mineralogical combinations. Yet, an aluminous clay content > 250 g kg−1 in combination with pedogenic Fe contents < 60 g kg−1 significantly promoted the formation of large macroaggregates > 4 mm. In contrast, a pedogenic Fe content > 60 g kg−1 in combination with aluminous clay content of < 250 g kg−1 promoted OC storage and persistence after the change in land use. The low clay-high Fe combination displayed the highest OC persistence, despite conversion of forest to cropland caused substantial disaggregation. Our data indicate that aggregation in this typical soil of the humid tropics is modulated by the mineralogical regime, causing moderate but significant differences in aggregate size distribution. Nevertheless, aggregation was little decisive for overall OC persistence in the highly weathered soils, where OC storage is more regulated by direct mineral-organic interactions.

Maximilian Kirsten et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on soil-2020-98', Jean-Thomas Cornelis, 22 Mar 2021
    • RC2: 'Reply on RC1', Anonymous Referee #2, 01 Apr 2021
      • AC2: 'Reply on RC2', Maximilian Kirsten, 03 May 2021
    • AC1: 'Reply on RC1', Maximilian Kirsten, 03 May 2021
    • AC3: 'Reply on RC1', Maximilian Kirsten, 03 May 2021

Maximilian Kirsten et al.

Maximilian Kirsten et al.

Viewed

Total article views: 328 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
241 73 14 328 14 3 4
  • HTML: 241
  • PDF: 73
  • XML: 14
  • Total: 328
  • Supplement: 14
  • BibTeX: 3
  • EndNote: 4
Views and downloads (calculated since 26 Feb 2021)
Cumulative views and downloads (calculated since 26 Feb 2021)

Viewed (geographical distribution)

Total article views: 292 (including HTML, PDF, and XML) Thereof 292 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 08 May 2021
Download
Short summary
Mineralogical combinations of aluminous clay and pedogenic Fe oxides revealed significant effects on soil structure and related OC storage. The mineralogical combination resulting in the largest aggregate stability do not better preserved OC during conversion of forests into croplands. Structural changes in the direction of smaller mean weight diameters do not cancel out the stabilizing effect of soil minerals.