In this project we investigate the role of soil aggregate turnover in controlling the amount and dynamics of organic matter in soils, and to quantify the reciprocal effects of organic matter decomposition on the formation and maintenance of soil aggregation. the hypothesis that a decreased soil aggregate turnover (due to the absence of soil disturbance by tillage) led to an increased stabilization of C within microaggregate structures under no-till compared to conventionally tilled systems. This hypothesis is tested by directly measuring the formation and degradation of the soil aggregates themselves as well as their associated organic matter fractions. We use a tracer approach employing ceramic microspheres (as soil microaggregate surrogates) to measure rates of formation and loss of various size classes of soil aggregates, along with our procedures for isolating aggregate-associated organic matter fractions in a set of laboratory and field experiments. The sites to be investigated will range across three sites representing a sequence of soil mineralogies, from a young, moderately weathered temperate soil (dominated by 2:1 silicate clay minerals) to a highly weathered tropical soil (dominated by 1:1 clay minerals and oxides). In the laboratory, we study the role of plant residues (amount and quality), soil texture and soil mineralogy on aggregate formation and the influences of dry-wet and free-thaw cycles on aggregate degradation.

In this research we seek a unified explanation of how the dynamics of soil structure (i.e. aggregate turnover) controls organic matter cycling that is applicable across broad domains of soil properties (temperate as well as tropical). The research contributes to improvements in our ability to simulate SOM behavior with mathematical model which are of critical importance for such applications as predicting soil quality, soil fertility relationships and the potential, through management of the sequestering C in soils to help mitigate greenhouse gas flux. Funded by the National Science Foundation

Macroaggregate structure: fungi (top right), bacteria (bottom right), microaggregates (top left) and particulate organic matter (bottom left)