Submitted to: Open Agriculture Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2013
Publication Date: 11/29/2013
Publication URL: http://handle.nal.usda.gov/10113/59048
Citation: Nichols, K.A., Halvorson, J.J., Caesar, T. 2013. Roles of biology, chemistry, and physics in soil macroaggregate formation and stabilization. Open Agriculture Journal. 7:107-117.
Interpretive Summary: In the near future, resources, such as water, synthetic nutrients, and pesticides, will be limited while agriculture production needs to be doubled to support a growing global population. Environmentally and economically sustainable agroecosystems which maximize the efficiencies of the entire system through sustainable intensification need to be developed. Soil aggregation is a key component of these systems, because it creates good soil structure for better water and gas movement into, throughout, and out of soil; reduces run-off and erosion; and improves nutrient cycling and biological activity. Macroaggregates are formed by spatially distributing soil components, such as clay minerals, sand, silt, and organic matter, close together and binding with ‘bags’ or nets created by roots and fungal hyphae, and ‘sticking’ these components together with ‘glues’. Stabilization of these aggregates occurs when cohesive forces binding the aggregate together are stronger than disruptive forces. This review discusses how biological activities, chemical reactions, and physical forces contribute binding forces for macroaggregate formation and bonding forces for stabilization. In addition, aboveground management systems, such as those including diverse crop rotations, reduced tillage, sustainable grazing, and using cover crops, which stimulate soil aggregation are identified.
Technical Abstract: Soil functions or ecosystem services depend on the distribution of macro- (= 0.25 mm) and micro- (< 0.25 mm) aggregates and open space between aggregates. It is the arrangement of the aggregates and pore space which allows air and water movement in and out of soil; reduces compaction; and stimulates microbial growth, soil organic matter (SOM) turnover, and nutrient cycling. Despite the importance of aggregates in soil, little is understood about how macroaggregates form and become stable. We hypothesize that biological activities, chemical reactions, and physical forces in macroaggregate formation 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 microbial biomolecules which increase the cohesiveness of the aggregate. This review focuses on the processes involved in macroaggregate formation and stabilization and how aboveground management impacts these forces.