Soil
Soil compaction
Soil compaction is soil pressed so tightly that its pore spaces shrink, which slows the movement of air, water and roots through the ground.
Soil compaction happens when soil particles are pressed together. University of Minnesota Extension says this reduces the pore space between them. Penn State Extension says compaction smashes a soil's pore spaces, stopping air, water, and root movement.
Heavy machines, foot traffic and wet ground all cause it. Compacted soil drains poorly and is hard for roots to enter, so grass and young trees grow badly there.
On a stump job, compaction matters when heavy equipment crosses a wet lawn, or when backfill is packed too hard. Lighter machines on tracks or tires spread weight, and dry ground helps. Loosen the top few inches before seeding. See after stump grinding.