Digging breaks up the network of channels and spaces in the soil. These are made by roots, soil organisms, wetting and drying, freezing and thawing. Those who rotavate, shred the worms!
Connecting spaces are an important component of soil macrostructure. They aid movement of water and air and facilitate root penetration.
Roots penetrate parallel to natural cracking.
Note the worm caste. Is there a centipede too?
Earthworm tunnels are particularly significant in providing continuities through the soil profile. Those that penetrate deep into the subsoil greatly improve drainage. Earthworm secretions harden the walls of their tunnels and give them a degree of permanence. Worms moving through tunnels have been eloquently described as pistons pushing pulses of air through the soil.
Probing roots also improve soil structure. The organic-rich rhizosphere maintained by organic root secretions and microrganisms is particularly significant.
In undisturbed soil, especially clay, natural cracks develop. It is significant that cracks reopen in a cycle of wetting and drying in the same positions each time. Perennial plant roots grow parallel to and within these gaps, a rich source of air and water.
Gardeners despise untidy cracks at the surface of clay soils, but these cracks provide an invaluable route for summer rainfall into the soil.
Significant message for those with clay soils
Clay soils benefit most by not digging. On sandy soils, the cracks and channels are much less stable. Fortunately, it matters less because as large sand particles lie together they create their own void spaces.
Undisturbed for decades, see how readily Worsbrough soil crumbles. The only weed control has been by spraying with glyphosate.