This month I spoke at the Organic Land Use Conference at the Atlanta Botanical Garden. I learned quite a lot! The focus of the meeting was soil health. Did you know soil is alive? It is absolutely teeming with all kinds of microbiology! It is a dynamic living ecosystem. There are more microbes in a teaspoon of soil than there are people on earth. Soil organisms are varied, versatile, and adaptable to changing conditions. They play a central role in making nutrients available to plants.
Types of soil microorganisms include:
Bacteria – Bacteria are simple, single-celled microorganisms. Bacteria inhabit a wide variety of habitats, including soil. A teaspoon of productive soil can contain from 100 million to 1 billion bacteria. Bacteria that improve soil quality feed on soil organisms, decompose organic matter, help keep nutrients in the root zone, enhance soil structure, compete with disease-causing organisms, and filter and degrade pollutants in soil.
Fungi – Fungi are a diverse group of multi-cellular organisms. The best known fungi are mushrooms, molds, and yeast, but there are many others that go unnoticed, particularly those living in soil. Fungi grow as long strands called hyphae (up to several yards long), pushing their way between soil particles, rocks and roots. Fungi that improve soil quality decompose complex carbon compounds, improve accumulation of organic matter, retain nutrients in soil, bind soil particles into aggregates, compete with plant pathogens, and decompose certain types of pollution.
Protozoa – Protozoa are microscopic, single-celled microbes that primarily eat bacteria. The bacteria contain more nitrogen than the protozoa can utilize and some ammonium (fertility!) is released to plants. Protozoa also prevent some pathogens from establishing on plants, and function as a food source for nematodes in the soil food web.
Nematodes – Nematodes are small, unsegmented round worms. Nematodes live in water films in the large pore spaces in soil. Most species are beneficial, feeding on bacteria, fungi, and other nematodes, but some cause harm by feeding on plant roots. Nematodes distribute bacteria and fungi through the soil as they move about. Predatory nematodes can consume root-feeding nematodes or prevent their access to roots.
Many soil microorganisms are known to be directly beneficial organisms, such as rhizobia and mycorrhizae. There are also a large number of soil organisms whose activities indirectly help plants decompose organic matter, which can transform nutrients into mineral forms that plants can use. As soil organisms break down organic matter, their activities help improve soil structure, providing a better environment for roots, with less soil compaction and better water and air movement.
Wow! That’s a lot going on beneath the ground that we can’t even see. Can you see why soil fertility is much more complicated than just doing a leaf or soil test, getting the results and adding the right amount of some nutritional component to the soil? It is alive and we want to do everything we can do to keep it living well. All of these microbes can be negatively affected by chemical pesticides and fertilizers. Large scale disruption of the soil can also be a problem for many soil inhabitants. Imagine all the worms getting chopped up by the tiller, all the fungal hyphae being torn to pieces and the sensitive aggregation of the soil being broken up and washed away.
We work very hard to maintain a good soil diversity and life. We use compost as our fertility, which is teeming with microbes. Instead of destroying life, it adds more life to the soil. Not only that, we continually try to add organic matter for the microbes to feed on and turn to plant nutrition. We lay a thick layer of straw between our cropping rows which provides shade, habitat and food for the soil good guys. Lastly, we don’t even like to till our land or run a tractor over it, although sometimes we must. For the most part, we lay out our planting lines and only till a strip where we want to plant, just enough to get a good seed line. We try not to ever totally till up a field.
Soil health is an ongoing process and isn’t easy. The soil is the key to the health of the crop and ultimately what provides the complex mix of nutrients that are in the fruit and vegetables! Our bodies need this mixture of complex plant nutrients. This is another great reason to be a member of a CSA or to find a great local grower at the market.
Eat your veggies!
Thanks to Dr. Holly Little, Acadian Seaplants Limited, for her assistance with parts of this article.