Cover crops (soil conditioning).
Cover crops are used for three different purposes -- as catch crops, green manures and living mulches.
Catch crops take up excess or residual nutrients remaining in the soil after harvest. These nutrients would be washed away or returned to the air (in the case of nitrogen), so binding them in a crop that decomposes in the spring can reduce fertilization needs. Catch crops can be winter-killed (they don't survive typical winter temperatures) or over-wintering. Buckwheat, oats, spring wheat, and crimson clover are winter-killed crops; fall rye, winter wheat and spelt, grasses and hairy vetch overwinter.
Green manures add nitrogen or organic matter (or both) to the soil. Bacteria known as rhizobia enter the roots of legumes like alfalfa, clovers and beans, and form nodules, converting nitrogen from the air into a form plants use. However, for legumes to add nitrogen to the soil, you'll have to plough them under intact, including the beans. If you've never grown legumes, you'll need to inoculate your soil with rhizobia before planting. Obtain the right type of inoculant for the legume(s) you'll be growing to ensure good nitrogen production.
Eliot Coleman, in his Four Season Harvest, suggests growing a small plot of alfalfa as a green manure to add nitrogen to the garden: simply mow it, rake it up and turn it under in your garden plot for a quick boost. You can cut it more than once during the season, and since it overwinters, it will grow again the next season.
Non-leguminous plants such as oats and annual ryegrass are good for adding organic matter. You can also use them along with legumes as effective smother crops. Jennifer Scott is a cover crop researcher in Nova Scotia and co-author of Under Cover: A Guide to Using Cover Crops in the Maritimes. She found that common vetch/oat and crimson clover/annual ryegrass combinations suppress weeds better than the grasses or the legumes alone. The seeding rate was one-half of normal for the grasses and two-thirds the rate for the legumes.
Living mulches grow around or beside your crop plants. They help prevent soil erosion by reducing rain's striking force on the soil and by taking up water that would move along the surface of bare soil. They also suppress weeds by blocking light, and help with insect control. Use a living mulch that establishes itself quickly, reducing the amount of bare soil for weeds to grow in. A fast grower may compete with your crop for water and soil nutrients; mowing the mulch or hoeing around individual food plants will ensure that they have the upper hand. Scott's research in 1995 revealed that broccoli thrived if transplanted a week before clover was planted; if it was transplanted with clover seeding, it was more stressed and could not form a canopy over the mulch.
The most useful cover crops are ones that provide more than one function. Cereal grains provide a food crop and organic matter; soybeans, field peas and broad beans yield a food crop (but won't provide much nitrogen if the beans are collected). If you are a beekeeper, alsike clover, broad beans, sweet clover, buckwheat and phacelia will give your bees a good supply of nectar.
As with other aspects of growing food organically, cover crops require that you know your soil and climate conditions, and that you watch for pest and competition problems. For example, Scott notes they found that "soil texture, organic matter levels, and initial fertility make a huge difference in the ability to establish effective cover crops." Some cover crops can harbour pest insects; others provide habitat for beneficial insects.
Crops that overwinter in warmer climates may winter-kill in the north. In drier climates, summer crops will compete directly with your main crop for nutrients and water. University of California Sustainable Agriculture Research and Education Program (UC SAREP) researchers found that almond orchards with cover crops used 20 to 25 percent more water than bare floor orchards.
While cover crops won't solve all your organic growing problems, they can play an integral part in your plans for a low-input, low-impact, sustainable lifestyle. If you plant cover crops this fall and next summer, your soil will return your investment with a bounty worthy of your efforts!
Under Cover is available for $10 (Canadian) plus $2 for postage and handling, payable to NSOGA Cover Crops. Mail your request to Janet Wallace, NSOGA Cover Crop Project, RR 1, Margaretsville NS B0S 1N0 or contact Janet by email at email@example.com.
Organic Field Crop Handbook is another useful resource on growing grains sustainably. It is available for $16.95 plus $3 postage and handling (Canadian or US dollars) from Canadian Organic Growers, Box 6408, Station J, Ottawa ON K2A 3Y6.
Here's the UC SAREP's Cover Crop Resource Page web site, which lists over 600 separate sources on cover crops: http://www.sarep.ucdavis.edu/sarep/ccrop/.
Jeff Johnston is the past president of Canadian Organic Growers and a Permaculture design course graduate. He has worked on conventional and organic farms, and gardens organically. He can be reached by email at: firstname.lastname@example.org.