How Soil Fertility Benefits from the Roots of Plants

I have been reading about the various ways in which soil fertility benefits from the sugar and other organic carbon compounds secreted from the roots of living plants. One source (here) states: “The ability to secrete a vast array of compounds into the rhizosphere is one of the most remarkable metabolic features of plant roots, with nearly 5% to 21% of all photosynthetically fixed carbon being transferred to the rhizosphere through root exudates.” These root exudates support microbial communities that help plant roots have continuous and simultaneous access to oxygen, water, and nutrients.

I’ve already written (here) about the way in which microbes help plants obtain nutrients (e.g., nitrogen, phosphorous, and minerals), but microbes also help roots access oxygen and water. Various organic “glues” produced by microbes, especially Glomalin, help bind mineral particles into small, irregularly shaped clumps known as soil aggregates. Like piles of rock or gravel, they don’t fit tightly together. When it rains, water flows easily through the countless gaps between soil aggregates, leaving empty spaces filled with air and films of moisture wrapped around the surfaces of the aggregates. This porous soil structure is optimal for plants since their roots have access to both oxygen and water at the same time.

How does this relate to backyard forest restoration?

Ideally, our restoration work helps native trees, shrubs, and groundcovers achieve their full potential. However, the actual restoration work often results in reduced vegetation (at least temporarily), not only from the physical removal of invasives, but also from the trampling of native plants, disruption of the microbial community, and disturbance of soil structure.

How can we minimize these negative impacts?

One thing we can do to minimize these negative impacts is avoid actual physical disruption of the soil. Examples include hand weeding instead of hoeing and staying off fragile slopes when the ground is saturated. Just as important however, since the fertility of the soil benefits from living plants, is to minimize barren ground. After invasive plant removal, we may have the time and money required for dense installations of natives, but if resources are limited, there are other options. In some places, especially sunny edges, I think a reasonable strategy is simply to keep the weeds mowed until native vegetation can be restored. Mainly, though, I continue to advocate variations of the Bradley method, tempering my zeal to remove all invasive plants as soon as possible, with the logic of proceeding at a gradual pace so that native plants have time to become established in successively cleared areas. To augment natural regeneration, there are a host of methods to restore vegetation, including transplanting, dividing, layering, live-staking, and even planting from seed. From this perspective, restoring backyard forests is less about clearing out weeds, and more about learning the skills and pleasures of gardening with natives.