Plant carbon and nitrogen contributions to the formation and function of soil aggregation processes in sustainable agroecosystems

Soil aggregate formation is controlled by crop and soil management, mineral, carbon and ion contents, internal drainage and associated weathering processes. Plant carbon (C) and nitrogen (N) components of soil organic matter (SOM) are key ingredients controlling the formation, function, and stability of soil aggregates. Although SOM content has been reported to be associated with aggregates of different size fractions, little is known of the soil C and N dynamics occurring within aggregates of different size fractions. Using stainless steel soil aggregate erosion (SAE) chambers, we have been able to identify multiple gradients within concentric layers from large numbers of individual soil aggregates ranging in size from 1-15 mm across. Soil tillage, cultivation, cover crops and rotations greatly modify the locations and concentrations of C, N, P and microbial communities within soil aggregates. Soil C recently deposited on aggregate surfaces is highly labile while most older and more recalcitrant C is sequestered in the central regions of aggregates. Soil aggregates associated with living roots of cover crops sequester much more N than shoot N or when plants are absent. A greater understanding of the dynamics within and at surfaces of soil aggregates will solve many mysteries of the magnificent root soil interface.