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 fine 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 significantly correlated with soil texture (clay+fine 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+fine silt fraction.
Highlights
The management and enhancement of soil organic carbon (SOC) is very important for agriculture as well as for the environment, mainly in tropical regions (Bernoux et al, 2006; Cerri et al, 2007) where development, food security, adaptation and mitigation have to be promoted in synergy (Bernoux et al, 2010)
SOC content was significantly correlated with soil texture and with soil MA amount while protected SOC content was not correlated with soil MA amount
This study aimed to identify among three soil parameters (SOC and macroaggregates contents, and soil texture), (i) which of them better correlates with the physical protection of SOC for 15 contrasted Malagasy soils and (ii) to discuss the main mechanism responsible for SOC accumulation in such soils
Summary
The management and enhancement of soil organic carbon (SOC) is very important for agriculture (fertility) as well as for the environment (carbon sequestration), mainly in tropical regions (Bernoux et al, 2006; Cerri et al, 2007) where development, food security, adaptation and mitigation have to be promoted in synergy (Bernoux et al, 2010). Relations between SOC and soil texture have been attributed to a chemical stabilization of SOC by physicochemical adsorption of SOC on soil clay/mineral surface (Feller and Beare, 1997). These relations showed that clayey soils have more potential for SOC storage than sandy soils (Siqueira Neto et al, 2010). SOC is commonly reported to correlate with soil macroaggregate amounts because SOC enhance macroaggregates formation by its action as a binding agent (Tisdall and Oades, 1982; Metay et al, 2007), and inversely macroaggregates may isolate and protect SOC against microbial attack (Beare et al, 1994)
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