Roots
I cut down my autumn raspberry stems yesterday, even though there were enough berries for a good bowl each after dinner. I also dug up all my remaining potatoes and left them to dry under a row of glass cloches.
In the poly tunnel, the old hands were discussing the gardening habits of the younger generation. The newer and younger allotters subscribe to the no-digging and raised bed view of life. I'm a digger, not from a love of hard work, but from conviction based on rigorous consideration.
The depth to which plant roots extend is often more than we suppose, since unless great care is taken fine roots are broken when a plant is lifted. The roots of Liatris pycnocephala penetrate to a depth of sixteen feet in its North American home, and I have seen Jacob pursuing Bindweed roots to a depth of seven feet.
All roots need to breathe, for which air is essential. In the process oxygen is absorbed and carbon-dioxide evolved. The latter, being heavier, tends to diffuse down between the soil particles, and the same gas is being costantly formed by the breathing of the billions of organisms which inhabit the soil. The soil thus has an atmosphere which is richer in carbon-dioxide and poorer in oxygen than the open air we breathe. The looser the texture of the soil, the more readily the soil atmosphere mixes with the open air above; and the converse is also true.
By digging, the gardener increases the ease with which the roots can penetrate to deeper levels, stabilising the plant and allowing access to usefull minerals. Further when the land is turned the soil atmosphere is mixed with the surrounding air, so that in every way the conditions for deep and healthy roots are improved.
When the no-digger spreads manure on the surface it is acted upon by multitudes of bacteria, which in their turn form the food of numberless protozoa, both of which add to the carbon-dioxide production, tending to replace the air. This is one of the reasons why some plants are intolerant of fresh manure, because it interferes with good aeration of the soil.
Most of the year I use a small cultivator in the top few inches of the soil, but once a year the plot is dug and the lower level broken up with a fork. This is the traditional method and I think it was evolved through many generations of acute observation by better gardeners than I.