Soils do not support weeds and crops equally well. We understand that different crops will have different nutritional requirements, different microbial associations, and grow differently in varying types of soil. Blueberries do not have the same nutritional requirements as alfalfa, which, in turn, has very different requirements from tomatoes. The same principle holds true for the plants we usually refer to as weeds. Weed plants are pioneering species. They are Nature’s primary method of remediating degraded soils, and can give clues to the mineral balance of the soil because they often will accumulate the minerals in which a particular soil is most deficient. Weeds accumulate the needed minerals in their tissue and return them to the soil as they are broken down by soil biology, gradually returning the soil to balance. They will also attempt to adjust soil characteristics like low organic matter, compaction, and nutrient excesses.
As soil conditions shift, weed populations can be expected to change as well. Once soil has reached a state of equilibrium, with balanced mineral ratios, thriving biological populations, and good aggregate structure, these pioneering species are no longer needed. At this point, the weeds will begin to lose vigor, and be attacked by the same diseases and insects that formerly infested the domesticated crops growing on these soils.