There are 10,000-50,000 species in just one gram of soil, whose nutrient-cycling services amount to $1.5-20 trillion in benefit annually, making it the world’s most valuable ecosystem, according to Dance and Tillman et al. (Soil organisms alone worth $1.5 trillion.)

These “soil livestock” are more diverse and numerous than tropical rain forest species, according to Eric Triplett, microbiologist at University of Florida, Gainesville.

How else can you improve your soil’s miles per gallon? Keep their roads open.

Root metabolism is handicapped when their underground highways (soil pore space) are blocked and their root networks shattered by tillage. These root networks are created mainly by beneficial mycorrhizal fungi (see photos). The bodies of these fungi are strands of fungal hyphae or thin threads, which increase the surface area contact with soil to gather more nutrients from the soil.

 “Tillage is very costly microbially, because it breaks down these aggregates, clogs soil highways and ruptures fungal networks that deliver nutrients to your crops,” Nichols says. “Tillage also exposes valuable organic matter to the air, releasing more soil carbon (microbes’ fuel) to the atmosphere.

“Compare a vase full of marbles to a vase full of sand,” Nichols says. Air and water move easily through the broad spaces between the marbles, but not through what little space exists between fine grains of sand (see photo). “In the same way, a healthy soil made of aggregates (marbles) has more pore space than a compacted soil (the sand).”

Preserving soil structure, or aggregates, preserves broad soil pathways for efficient two-way exchange of vital nutrients, gases and moisture. Tillage and compaction clog underground avenues by disintegrating soil aggregates that choke traffic.”