Comparative carbon stability in surface soils and subsoils under submerged rice and upland non-rice crop ecologies: A physical fractionation study

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Research Article

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The role of subsoil to store stable carbon (C) has become an important research topic in recent decades. In doing so, pools of subsoil C are compared to surface soil. The present study identified differences in mineral associated C (as separated by density fractionation) and aggregate occluded C in surface and subsurface soils. It also considered the impact of submerged rice as well as upland non-rice ecology on soil C stability. Results indicated that subsoil had a significantly greater amount of soil microaggregates as well as microaggregates within macroaggregates compared to surface soils. Subsequently, subsoil also had higher microaggregate occluded C, inaccessible to microorganisms. The higher ‘ratio of C present in the heavy density fraction with C present in bulk soils’ suggested that more C was strongly associated with the subsoil mineral fraction. Besides, spectroscopic analysis of functional groups indicated higher stability of subsoil aggregate occluded C than the aggregate C of surface soils. Summarily, results indicated that subsoil is a potential niche for recalcitrant C storage. Contrariwise, submerged rice ecology resulted in marginally higher soil aggregation compared to upland non-rice soils. Crop ecology did not influence aggregate occluded C dynamics and mineral-C association. As soil physical and aggregation dynamics differ substantively in puddled rice soils and upland non-rice soils, more research is warranted before making a strong conclusion.

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