12.3.1: Introduction
- Page ID
- 37982
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Where no kind of manure is to be had, I think the cultivation of lupines will be found the readiest and best substitute. If they are sown about the middle of September in a poor soil, and then plowed in, they will answer as well as the best manure.
—Columella, 1st century, Rome
What is the single best thing you can do to help your soil rebuff the effects of gardening and farming? Yes, it is cover cropping. You were introduced to cover crops earlier in this chapter and here we go into more detail.
Cover crops have been used to improve and protect soil and the yield of subsequent crops since antiquity. A cover crop does just what its name implies. It covers the soil in a blanket of green. When it is not 'growing season' the mat of dead or dormant plant material on the surface is also very protective against wind and water that tries to sweep soil off the field. The best cover remains in place, a living blanket, and living, soil-holding roots all year around. That kind of blanket can be found on a managed grazing farm. But, most of our annual crops need some sort of entry point, a way to get seed in the ground and for that reason, cover crops are often turned under to allow for seedbed preparation. When a green, growing cover crop is plowed down into the soil it becomes 'green' manure.
Chinese manuscripts indicate that the use of green manures is probably more than 3,000 years old. Green manures were also commonly used in ancient Greece and Rome. Green manures add the plant material plowed down back into the soil adding nutrients and organic matter. However, at that point, the cover crop ceased being protective against erosion.
Today, there is a renewed interest in cover crops, and they are becoming important parts of many farmers’ cropping systems. A cover crop is usually grown with multiple objectives beyond protecting the soil with living vegetation during a time of the year when it would otherwise be bare. Cover crops' other benefits include:
- using the sun’s energy and CO2 from the atmosphere to sequester carbon
- increasing soil organic matter with their roots and surface residue
- protecting nitrates from leaching
- increasing the amount of soil nitrogen (especially using legumes)
- breaking up soil compaction
- providing habitat for beneficial organisms
- promote mycorrhizal fungi presence for the following crop.
Cover crops are usually killed on the surface or incorporated into the soil before they mature. (This is the origin of the term green manure.) Since annual cover crop residues are usually low in lignin content and high in nitrogen, they typically decompose rapidly in the soil.
Cover crops are usually not perennial but they can be in a garden setting. Many commercial-scale gardens use white clover as a cover crop on pathways between beds and fields. White clover is low growing, needs mowing infrequently, keeps weeds from invading, and saves the gardener a lot of work trying to keep paths, alleys, and headlands free of weeds. It also attracts pollinators to the garden--a special benefit.