Carbon sequestration in clay and silt fractions of Brazilian soils under conventional and no-tillage systems

Abstract

The capacity of soils to sequestrate carbon (C) is mainly related to the formation of organo-mineral complexes. In this study, we investigated the influence of soil management systems on the C retention capacity of soil with an emphasis on the silt and clay fractions of two subtropical soils with different mineralogy and climate. Samples from a Humic Hapludox and a Rhodic Hapludox, clayey soils cultivated for approximately 30 years under no-tillage (NT) and conventional tillage (CT) were collected from six layers distributed within 100-cm soil depth from each site and from an adjacent native forest. After the removal of particulate organic matter (POM), the suspension (<53 µm) was sonicated, the silt and clay fractions were separated in accordance with Stokes' law and the carbon content of whole soil and physical fractions was determined. In the Humic Hapludox, the clay and silt fractions under NT showed a higher maximum C retention (72 and 52 g kg , and no difference was observed whether under an NT or a CT management system. The predominance of goethite and gibbsite in the Humic Hapludox, as well as its exposure to a colder climate, may have contributed to its greater C retention capacity.In addition to the organo-mineral interaction, a mechanism of organic matter self-assemblage, enhanced by longer periods of soil non-disturbance, seems to have contributed to the carbon stabilization in both soils.

Carbon in Physical Fractions and Organic Matter Chemical Composition of an Acrisol after Amazon Forest Burning and Conversion into Pasture

“…Contrastingly, the relation between C soil and C clay contents in BAF area showed an exponential behavior tending to saturation (Figure 6a) and the maximum C rc in clay fraction was estimated from the equation in Figure 6a as 81 g kg -1 . Reis et al, 19 using the same approach, obtained lower values for maximum C rc for two heavy clayey Brazilian subtropical Oxisols (25 to 72 g kg -1 ) under different soil management systems. The comparatively higher C rc value observed in our study can be attributed to the substantially lower C soil content in BAF compared to that observed by the authors in the Oxisol.…”

“…These findings highlight the role of organo-mineral interactions as a mechanism for organic matter protection, particularly interactions with clay, due to its greater surface area in comparison to sand and silt. 19,42,43 The most outstanding difference on C sand content was observed at 0.00-0.05 m, where values decreased in the order: BAF > NAF > BRA (Table 4). Greater accumulation of C in coarse fractions in areas under forest can be expected, once plant residues deposited on forested soils tend to be coarser than residues of pasture.…”

“…Soil samples from depths 0.00-0.05, 0.05-0.10, 0.20-0.30, 0.40-0.50, 0.75-1.00 and 1.00-1.50 m were subjected to particle size fractionation (in duplicate) according to Reis et al 19 In a 100 mL glass tube, 15 g of soil and 50 mL of distilled water were added. The suspension was mechanically shaken in horizontal position for 16 h and thereafter passed through a 53-µm sieve.…”

“…17 Studies dedicated to investigate C saturation levels in mineral soil fractions have been performed in soils under agricultural management. [18][19][20] In Amazonian soils, studies on C retention capacity and saturation of silt and clay are scarce, and could elucidate the effectiveness of undisturbed and fire-affected soils either under natural regeneration or pasture to sequester C.…”

Soil Organic Carbon in Mangrove Ecosystems with Different Vegetation and Sedimentological Conditions

“…XRF analysis of soils/sediments in terrestrial and mangrove ecosystems. As clay had high carbon capturing capacity [17,35], the high clay content in the mangrove mud layer was responsible for the high carbon sink capacity of the mangrove (Table 4). The mud layer had comparable clay content to the mangrove mud layer, but its carbon content was not high.…”