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Secrets in the Soil
By Leslie Roberts, with Bill Bruneau and Jamie Chevalier, Bountiful Gardens Staff

Unlock the Secrets in the Soil

It has only recently been discovered how wild plants and flowers reach maturity without someone to fertilize, till, or water them. An important clue lies not in the plants themselves but in the network of fungi that connect them.

One of the secrets of healthy, resilient soil is to rebuild a nourishing rhizosphere—the narrow region of soil that is directly influenced by root secretions and associated soil microorganisms. Frequently as soil energy and nutrition improve, so does the population of healthy fungi and other microorganisms that play an essential part in developing soil. Sometimes the soil can benefit from the addition of fungi.

A vital member of a healthy rhizosphere is mycorrhizal (my-co-RY-zal) fungi. Unknown to most, mycorrhizal fungi colonize the roots of over 90% of plant species. Fungi aren't just mushrooms; mushrooms are actually the fruit of the fungi. The majority of the fungus is a network of threads underground, running through yards or miles of soil. Most trees and agricultural crops depend on or benefit substantially from mycorrhizae.

These fungi form a mutually symbiotic relationship with the roots of a plant, allowing it to take up many times more nutrients than would be possible without the fungi. Mycorrhizae scavenge for hard-to-find nutrients, passing them on to plants. They also move nutrients around from surplus areas to areas where nutrients are in short supply, for example, from areas of soil under nitrogen fixers to areas of heavily cropping fruit trees.

Mycorrhizal fungi can free up insoluble nutrients by secreting powerful organic acids that lower the soil pH, making it more acidic, which helps to make bound nutrients soluble. The fungi then transfer these nutrients to the associated host plants, helping them compensate for low nutrient availability, poor soil structure, and low water-holding capacity. In turn, these fungi receive carbon from the plant host, which is used for fungal growth.

Of course, the number of plants that mature, and how large they get, depends on a reasonable supply of nutrients being in the soil. In addition, many wild plants are specialists and do not need much in the way of certain nutrients. Therefore they thrive in soil where certain nutrients are deficient, where others cannot.

In addition to making bound nutrients soluble, the fungi also make heavy metals soluble. These metals are then trapped and immobilized by being stored in mycelium outside the root, thus preventing the plant from taking them up. In this way, the fungus protects the plant from contaminants and assists the plant's growth in hazardous areas. This process, known as mycorestoration, makes the heavy metal inaccessible to the plants.

Mycorrhizal fungi also help plants resist pests. Most experts in pest management report that plant health is the most important aspect of pest management. Healthy plants have a good deal fewer pest problems. Better nutrition and water uptake through mycorrhizae help plants stay healthy.

Healthy soil is dependent on soil microorganisms. Develop vital soil that supports these microbes by improving soil organic matter and minimizing tillage unless the soil needs added air. Reintroducing mycorrhizal fungi into our soil can be an important step in the process of healing damaged, depleted, and contaminated soil. Even in garden soil that's already productive, adding mycorrhizal fungi dramatically improves the health and productivity of plants.

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