In:
SOIL, Copernicus GmbH, Vol. 7, No. 2 ( 2021-07-06), p. 363-375
Abstract:
Abstract. Aggregation affects a wide range of physical and biogeochemical soil
properties with positive effects 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
aluminosilicates, aluminum hydroxides, and Fe oxides are part of the
clay-sized fraction it is hard to separate how certain mineral phases
modulate aggregation. In addition, it is not known what consequences this
will have 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 land uses, 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, and changes in
aggregation and OC contents under forest and cropland land use. Patterns in
soil aggregation were rather similar across the different mineralogical
combinations (high level of macroaggregation and high aggregate stability).
Nevertheless, we found some statistically significant effects of aluminous
clay and pedogenic Fe oxides on aggregation and OC storage. 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 even under agricultural use. The
combination with low aluminous clay and high pedogenic Fe contents displayed
the highest OC persistence, despite conversion of forest to cropland causing
substantial disaggregation. This indicates that aggregation in these
tropical soils 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 these highly
weathered soils, where OC storage is more regulated by direct
mineral–organic interactions.
Type of Medium:
Online Resource
ISSN:
2199-398X
DOI:
10.5194/soil-7-363-2021
DOI:
10.5194/soil-7-363-2021-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2021
detail.hit.zdb_id:
2834892-8
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