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Photo courtesy of MAUREEN GILMER via Scripps Howard News Service Legumes such as beans grow better when a specific microbe is present in the soil.
Sunday, April 8, 2012

Microbes boost plant production

Organic food gardening always will be about the soil.

Natural soil isn’t just mineral grains and organic matter. It contains living microbes such as bacteria, algae, fungi and other organisms. Each serves a purpose.

The most important to plant growth is a group of fungi known as mycorrhizae. The microscopic fungi actually grow into the plant, entering through tiny root hairs. Once inside, they remain for the life of the plant.

The fungi aren’t parasites, but are symbiotic, which means they aren’t harmful to the plant. In fact, mycorhizzae established within plants make them stronger, more productive and disease-resistant.

Long ago, it was discovered that peas and other legumes gather nitrogen from the air and concentrate it into the soil. This process is called nitrogen fixation. This is achieved only with the help of certain mycorrhizae, which are present in most soils.

Once the seed germinates, its roots seek out these microbes, which are sometimes few and far between. The sooner the root finds mycorrhizae, the sooner it carries on nitrogen fixation.

Ordinarily, it takes a long time for naturally occurring mycorrhizae to thoroughly integrate with the plants. This takes longest in bagged soils where it had been absent altogether, or in first-year gardens where populations are low.

Savvy gardeners know they can speed up this process to help their peas and beans connect with this microbe. Early microbe establishment ensures a more abundant nitrogen supply in the earliest part of the plants’ life cycle.

There’s a way you can fast-forward the process when planting peas. Most seed catalogs offer a product called inoculant, which is a canned powdered form of the specific strain of mycorhizzae living within legumes. You roll your pea and bean seed in this stuff just before you plant it. This puts high numbers of microbes in direct contact with the germinating root from the moment it hits the soil.

There is another benefit to inoculating peas with mycorhizzae. Once the fixation process begins, the plant stores nitrogen in the root, stem and leaf. By the time the crop is in and plants have run their course, an inoculated pea plant will contain far more nitrogen than other peas left to fend for themselves.

That means more nitrogen was fixed into the soil around the roots of the pea. When the spent plant is tilled in or put into a compost pile at the end of the season, its tissues hold concentrated nitrogen. In fact, the place where that pea grew will produce outstanding leaf crops the next year because of this nitrogen concentration in the soil.

Consider every spent inoculated pea plant a high-potency source of organic nitrogen.

Understanding how mycorhizzae integrate with plants is essential to getting the most from your garden. Choosing potting soil that contains mycorhizzae will make your plants grow better.

Inoculate your pea and bean seeds to make sure they get off to a screaming start. Do this and you aren’t just growing food, you’re cultivating an entire world of microbes.

In the end, it is these tiny organisms you can’t see that may make the biggest difference in what you can.

Maureen Gilmer is an author, horticulturist and landscape designer. Learn more at www.MoPlants.com. Contact her at mogilmer@yahoo.com or P.O. Box 891, Morongo Valley, CA 92256.