Impact of clay content on soil microaggregate arrangement and organic matter.

Aggregation confounds soil particles of different sizes into a larger architecture. Such mixtureimpedes resolving which particles build aggregates and how these control the accumulationof soil organic matter (OM). We used a novel method to differentiate microaggregates(<250 μm) from dispersed particles based on a dynamic image analysis in water. To identifythe impact of soil texture, we analyzed 25 topsoil samples of an arable site in Scheyern(Germany) with a gradient in clay content of 16-37 % clay and organic carbonconcentrations of 10-15 g kg1. We found that soils with a higher clay content containedlarger microaggregates and more occluded ones. The soils with lower clay contents consistedof less occluded microaggregates while the <53 μm aggregates contained higher OMconcentrations. This shows that in the low clay soils a similar amount of OM couldbe held despite containing fewer fine particles and less occluded aggregates. Theadditional OM in the low clay soils was decoupled from the BET specific mineralsurface area which remained constant across the clay gradient. Soils with a highercontent of fine particles were related with the increased preservation of OM throughaggregation and occlusion. Our data reveal that a higher fine particle content buildslarger soil microaggregates and allocates more OM into occluded aggregate units. [ABSTRACT FROM AUTHOR]