Roles of Biology, Chemistry, and Physics in Soil Macroaggregate Formation and Stabilization

Many soil functions depend on the distribution of macro- (≥ 0.25 mm) and micro- (< 0.25 mm) aggregates and open space between aggregates (i.e. soil structure). Despite the importance of macroaggregates in soil, little is understood about how they form and become stable. We hypothesize that biological activities, chemical reactions, and physical forces which help to form macroaggregates differ from those involved in stabilization. Formation is a binding process where aggregate components are brought spatially closer together, ‘bagged’ or enmeshed by roots and fungal hyphae and ‘glued’ by labile SOM. Stabilization involves bonding processes between organic matter, clay minerals, cations, or plant or microbial biomolecules which increase internal cohesiveness. By separating aggregate formation from stabilization, the biological, chemical, and physical processes involved in maintaining long-term soil quality through stabilized soil structure will be more easily identified.