Getting microbes on your team: Soil food web basics

When I started at Rincon-Vitova in July, I saw a book in the break room called Teaming with Microbes: A Gardener’s Guide to the Soil Food Web. I’ve been gardening whenever I have the space since I was eight and plants are so interesting to me that I got a biology degree focused on them, but I’d never heard of a soil food web before. I know mostly about the macroscopic parts of a garden ecosystem: dirt, water, plants, and bugs. Of soil microbiology, all that was usually mentioned in my botany classes was the nitrogen-fixing Rhizobium bacteria and mycorrhizae, the fungi that help plant roots reach farther and absorb more. Books and websites I read to further my hobby talked about the negatives of soil biology – nematodes, wilts, damping off. This looked like an interesting change of pace. So I picked up the book and started reading.

The part of the soil food web that you can see – the bugs and earthworms around a plant’s roots – rely on an entire microscopic world of bacteria, fungi, nematodes, and protozoa. You’ve probably heard about the qualities of good soil: dark, moist, full of organic matter and earthworms. Besides being able to hold water well, this soil supports life. Land that’s been used for intensive farming and land that has recently been developed is missing this key living component. This is part of the reason why home gardeners are seen fertilizing their lawns and battling fungal diseases regularly. Dirt with no life in it doesn’t support life very well.

The microbes in soil can help plants in a few different ways. I mentioned mycorrhizae earlier. They are fungi that evolved a handy symbiosis with plant roots. The roots secrete simple sugars at the root hairs. In exchange for this food, the mycorrhizal fungi pass water and nutrients to the plant. Of course, plants can absorb nutrients and water without the fungi, but the fungi increase the amount and range of stuff the roots can absorb. Besides mycorrhizae, there are microbes that help break down decaying material and unlock the nutrients, microbes that bind soil together into water-holding clumps, microbes that release chemicals that stimulate plant growth, and microbes that protect the plants from other microbes. The last category is one that many gardeners probably notice without realizing it. Without the defense of beneficial microbes, plants are vulnerable to root-knot nematodes and a whole slew of fungal diseases. There are a few ways gardeners can help out these microscopic workers. Incorporating compost, manure, or other organic matter into the soil can give the microorganisms already there a moist and comfy home, as well as a food source. If a lot of the microbes have been killed off, they can be replenished with a well brewed compost tea. Commercial inoculants of specific species are also available. There are many facets of a health soil food web. As I learn more about the soil food web, I’ll share it with you.

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