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Cover crops are planted to prevent soil erosion, improve soil health, reduce weed populations, provide habitat for insects and wildlife, increase diversity of plant life, and to help manage water availability on your farm. Economically, preventing top soil erosion and improving soil health will provide long term yield benefits for your crops. Here are some things to think about when picking a cover crop:
It is important to be clear on your cover crop objectives when choosing a cover crop. Some of the common objectives are listed below:
1) I want to improve the soil by adding nitrogen or organic matter or I want to reduce the N or other nutrients in the soil:
If you are looking to add nitrogen to the soil, you may want to add a legume (clovers, vetch, peas, beans) to your cover crop blend. They also provide habitat for insects and pollinators, provide some organic matter benefit and have some soil erosion benefit.
If you think you have excess nitrogen in the soil that could be lost through leaching and run off potentially contaminating water and causing algae bloom, you can try to tie that up by planting a cover crop that will scavenge those nutrients and keep them in the field to be released back for the next crop when the plants decompose, then you would want to plant a non-legume like cereals, forage grasses or brassicas, buckwheat or sunflower.
2) I want to reduce soil erosion
In windy southern Alberta it is very important to control soil erosion. Non legume cover crops are best for this purpose
3) I want to conserve soil moisture: Dryland farmers often fear that cover cropping will take too much moisture out of the soil. However, tests have shown that mixes of cover crops are more frugal with water and by preventing weeds they reduce water consumption. In addition, the plants can capture snow during the season and if left as a mulch in a no-till scenario, the mulch can conserve moisture into the summer.
4) I want to protect my fragile plants: Putting a cover crop with seed canola or mustard can prevent these plants from being damaged by wind shear when they are little and help them get established.
When seeding a cover crop with another crop, seed your cover crop at 1/3 to 1/2 of your normal seeding rate.
An interesting tool is available from the University of Minnesota Extension - University of Minnesota Extension - Cover Crop Decision Tool: Take caution with the seeding dates there but it is quite helpful to see which plants best meet your cover crop objectives.
4) I want to prevent weeds: Putting in a cover crop generally suppresses weeds by providing competition for nutrients and moisture in the soil. However, there are some cover crops that produce allelopathic chemicals that suppresses other plant growth and therefore can be more effective at reducing weeds. Plants to consider that do this include rye and mustard. Care must be taken though to ensure the cover crop is terminated a week or so before seeding again in the spring so that there is no negative effect on the next crop.
When seeding a cover crop with another crop, seed your cover crop at 1/3 to 1/2 of your normal seeding rate.
1) Seeding Date: A fall cover crop has to grow enough before freezing to provide some protection for the soil, so normally it is recommended to seed your cover crop prior to Sept 15th. If you graze a cover crop, you need to allow the crop enough time to recover so that it can get to at least 6 inches of cover crop growth for winter coverage benefits (and to meet RDAR cover cropping requirements).
2) Seeding rate: Can depend on your method of seeding. For potato fields for example: - before harvest: One method used for seeding cover crops is to broadcast the seed on the potato field prior to harvest. Recommended seeding rate of 2 bushels per acre. When the potato is harvested, some of the cover crop seed is incorporated into the ground. After harvest: Alternatively, if you seed after harvesting potatoes with a drill, it can be very difficult to seed with potato vines, however, the seeding rate can be reduced to 3/4 to 1 bushel per acre.
3) Will you be harvesting your cover crop or just terminating it? Will your cover crop be harvested for forage purposes or for a spring crop e.g. Winter Wheat or Fall Rye. If so, you will want to seed those cover crops at their normal rates, but for annual crops that you are planting solely for soil erosion purposes, generally we would recommend seeding at 1/2 to 3/4 normal rate. We find Oats and Barley are an economical choice and they work well for quick germination and rapid growth for a cover crop that will be terminated without harvesting.
Cover crops are one of those areas where there are many options and many considerations. However, cover crop blends can get very expensive depending on their components. If you are looking for an economical multi-species blend, we would recommend simply an oats/forage pea blend or barley/forage pea cover crop blend.
