Vertical Distribution of Soil Organic Carbon In Vertisols.

Soils of the world store more carbon than what is present in biomass and in the atmosphere, so the depth and distribution of soil organic matter (SOM) might be important in carbon sequestration and climate change mitigation. Texture, among several other factors, plays an important role in the distribution of SOM. Most national and the main international soil classification systems (Soil Taxonomy, World Reference Base for Soil Resources) have separate categories for high clay content soils on the highest level of classification as Vertisols. Due to the high swelling clay content, these soils open deep cracks when they are dry. During the process called “pedoturbation”, the high SOM content surface material falls into the cracks, where it accumulates and mixes with subsoil, and enhances the accumulation of SOM in great depth. Although the effect of texture on the stabilization, distribution and properties of SOM have been investigated, only little information is available on SOM distribution in high clay content soils. The objective of this study was to analyze the vertical distribution of SOM in high clay content soils that occur in Hungary and Texas. Our results, based on the investigations of the USDA-NRCS soil characterization database and the Hungarian TIM database support the hypothesis that high clay content soils store significantly more SOM and in greater depth than other soils under similar climatic conditions.