 |
|
|
|
| |
The Garden Plot for February 22, 2008
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: "Winter Fallow"
The recent warm temperatures and resulting thaw reminded me just how bad winter fallow is for the soil. Winter fallow is the practice of leaving garden or farm soil bare over the winter. Usually winter fallow follows an annual crop the previous summer. During our early February thaw, I visited a nearby vegetable farm and was horrified to see dark rivulets of water trickling over the bare soil into a ditch flowing with muddy brown water. Even though most of the soil was frozen, the very surface was eroding away with melting snow. Nobody wants to see even small amounts of soil erosion. But another concern is that this surface layer is often the layer that contains the highest amount of soil organic matter and the soil food web.
The soil food web is an interconnected complex of living organisms including bacteria, actinomycetes, fungi, protozoa, as well as earthworms, nematodes, yeasts, algae, and insects. In a healthy soil, 1/4 teaspoon of topsoil can contain up to one billion soil microorganisms, including:
100 million to 1 billion bacteria.
10 million to 100 million actinomycetes, and
100,000 to 1 million fungi.
Winter fallow is not the best management choice for our Soil Food Web. Many players in the soil food web are killed by the repeated freeze – thaw events that occur in soil left un-covered over the winter. Studies in Oregon found lower numbers of soil microbes in soils that had been left bare over the winter compared to soils with a winter cover crop. Compaction may also increase on soils left without cover all winter. In compacted soil, structure (or good tilth) is broken down. A healthy soil consists of stable particles surrounded by air space. Picture a jar filled with marbles. As soil structure breaks down, during compaction, soil particles come to resemble grains of salt in a jar instead of marbles. There is little air space between the soil particles. Then, the soil cannot supply sufficient oxygen for the soil food web, or for plant roots. Soil organic matter levels also decrease when soil is exposed to the weather all winter. Soil organic matter is the main energy and food source for our soil food web. It is also the framework for organic soil fertility management and natural disease suppression. For all these reasons, gardeners and farmers should avoid winter fallow when possible.
The best way to avoid winter fallow is to over-sow perennial rye grass or clover into gardens at the end of the growing season in September. You can also mow leftover residues in your garden and leave them on the surface (as long as you did not have insect or disease problems). Wait until spring to actually till the garden. If insects and diseases were a serious problem in your garden, you can remove affected plant material, add a well-decomposed compost, and mulch the area instead of mowing and leaving crop residues on the surface.
Mulched and cover crop soils warm up more slowly in the spring if you don’t get in and remove mulches or till in cover crops early. However, though it may be a bit more work to prepare your garden or farm soil in the spring, the benefit to soil health when you keep your soil covered over the winter is worth it.
Helen Atthowe's new short program of gardening tips
|
|
|
