Soil Structure Across Scales: The Energy of Soil Aggregation.

Soil covers more than 13,000 million hectares of the earth’s land surface, of which 1500 million hectares are used as cropland. Significantly, about 10,000 million hectares of surface soil is aggregated giving increased water infiltration, water holding, decreasing runoff and erosion and improving the soil’s resilience. Theoretically 4 x 10¹⁵ MJ of energy is stored in these soils, global changes including climate change and energy insecurity can provide negative feedbacks to soil aggregation. The degradation of soil structure releases the internal energy of the soil, i.e. the energy that holds together the aggregates, further contributing to climate forcing. Energy is nature’s global system currency, and knowing this fundamental intrinsic energy of soil aggregates allows us to place soil as part of the ecosystem, understanding how much energy is required to maintain aggregation, and in-turn to function. The knowledge of energy allows us to provide the link of energy flow of major ecosystem functions in soil. This paper will demonstrate an energy approach for the quantification of soil’s intrinsic energy of aggregation. At a laboratory scale, the energy responsible for dispersing soil aggregates is quantified through the use of ultrasonic agitation. This intrinsic property of soil aggregates corresponds to the strength of their inter-particle bonds. This laboratory approach is limited in application as it is tedious, we then discuss how we can get a picture of the spatial variability of soil structure in the field using proximal soil sensors.  We then discuss the possibilities of the relationships between aggregate bond energy with soil parameters that are more easily-measured. And finally, the potentials of relating all these measurements across scales.