Farm manure and leaf mould belong to an art that was old when history was young. It is the task of the modern writer to set out the meaning of the gardener's words, with the explanations science provides. However, science never knows everything and we shall be in some danger if we forget the old gardener's talk. Our explanations are not a generation old and that is too short a time to test them. I find nothing wrong with his explanation.
Fertility is represented in the soil by fibre and goodness.
Cultivation hastens the transfer of this to the crop. Fibre and goodness must be returned to the land if fertility is to continue. And his explanation has worked out right since the days of Tudor gardening.