Texture and organic carbon contents do not impact amount of carbon protected in Malagasy soils

Abstract

Soil organic carbon (SOC) is usually said to be well correlated with soil texture and soil aggregation. These relations generally suggest a physical and physicochemical protection of SOC within soil aggregates and on soil fi ne particles, respectively. Because there are few experimental evidences of these relations on tropical soils, we tested the relations of soil variables (SOC and soil aggregate contents, and soil texture) with the amount of SOC physically protected in aggregates on a set of 15 Malagasy soils. The soil texture, the SOC and water stable macroaggregate (MA) contents and the amount of SOC physically protected inside aggregates, calculated as the difference of C mineralized by crushed and intact aggregates, were characterized. The relation between these variables was established. SOC content was signifi cantly correlated with soil texture (clay+fi ne silt fraction) and with soil MA amount while protected SOC content was not correlated with soil MA amount. This lack of correlation might be attributed to the highest importance of physicochemical protection of SOC which is demonstrated by the positive relation between SOC and clay+fi ne silt fraction.

Alterações no carbono orgânico do solo de campo natural submetido ao plantio de <i>Pinus taeda</i> em três idades

“…In this sense, it is worth mentioning excess moisture and very low temperatures (BALDOCK; NELSON, 2000), as well as the physical protection within soil microaggregates (CAMBARDELLA; ELLIOTT, 1993;FELLER, 2000;SIX et al, 2000) and chemical protection by bonds between organic and clay mineral compounds (PARFITT et al, 1997). However, in this study, the soil clay content was not the preponderant factor for OC accumulation, as reported elsewhere by Razafimbelo et al (2013). Therefore, the pine trees were decisive for soil TOC accumulation, as also shown by the negative correlation between the TOC and clay contents, and because the TOC levels and their POC and MAC fractions were highest precisely in the soil with the lowest proportion of this particle-size fraction.…”

Importance of soil physical characteristics for petroleum hydrocarbons phytoremediation: A review

“…This accumulation and binding process is driven predominantly by the organic carbon content of the fractions (Tan et al, 2007;Guimara et al, 2013;Razafimbelo et al, 2013). The degrading microbes of PAHs were also distributed un-evenly through out the soil particles with different sizes (Razafimbelo et al, 2013). The collaboration of organic matter in soil for building aggregates in several land use managements had, variety of influences on the fate of PAHs, reported by Xiao et al (2014).…”

“…In an experiment referring to the interaction between soil aggregation and hydrocarbon contamination Amellal et al (2001) indicated that, more PAHs were found in the smaller size fractions (clay < 2 µm and fine silt 2 to 20 µm) compared to the sand and coarse silt. This accumulation and binding process is driven predominantly by the organic carbon content of the fractions (Tan et al, 2007;Guimara et al, 2013;Razafimbelo et al, 2013). The degrading microbes of PAHs were also distributed un-evenly through out the soil particles with different sizes (Razafimbelo et al, 2013).…”

“…Commonly these agents could be very simple plant residues (different organic materials) with low density and when incorporated with soil it lowers the bulk density and increase porosity and oxygen diffusion and further help building water-stable soil aggregates. These materials include vermiculite (inorganically), and saw dust, wheat bran, hay and other grass residues organically enhance jointing soil particle together and consequently increase aeration, microbial activity and thus hydrocarbon degradation (Razafimbelo et al, 2013). In respect to soil aggregation and remediation processes some other complexities like root growth and functions, soil water status and chemical properties (i.e.…”

“…In another experiment, Kaimi et al (2007), by cultivating twelve plant species measured the changes in total petroleum hydrocarbon concentration, soil dehydrogenase activity and the number of aerobic bacteria and concluded that TPH concentration was more dependent to the soil dehydrogenase activity than to the aerobic bacterial number. Several experiments (Metay et al, 2007;Razafimbelo et al, 2013) showed that crushing soil aggregates would enhance respiration (higher CO 2 ), which results in additional carbon mineralization as SOC pool, physically protected in soil aggregation. In cases when oxygen is absent or limited, biodegradation can occur anaerobically.…”