[mountaintimefrm]

> Water infiltration is measured by digging a small hole, filling it with water, and seeing how fast it drains.

Informally yes, but the scientific way is to use a ring infiltrometer: https://www.fao.org/3/s8684e/s8684e0a.htm -- Basically instead of digging a hole, you pound a pipe into the ground and then fill the pipe with water.

As for agricultural practices being able to change soil composition multiple feet down, trees and tap-rooted plants are very effective at placing large volumes of organic matter at depth. One example, Lacy Phacelia (Phacelia tanacetifolia) is an annual plant that produces a dense fibrous root system that reaches a depth of 4 feet; in the fall the Phacelia plants die, and their roots decompose at depth, creating pathways for water infiltration while also increasing soil organic matter at depth. The same goes with other trees and shrubs. The farmer from the "It ain't much but it's honest work" meme, Dave Brandt, has some really enjoyable presentations on youtube about improving soil composition at depth.