By Natalie Rector
Some say cover crops are a relic of the horse-and-buggy days of agriculture. But a well-established cover crop can turn nutrients into cash by tying up precious nitrogen until spring, when a new crop is ready to use it.
This is especially true in fields that receive manure applications in the fall. Roots and top growth from cover crops soak up manure nutrients until they can be recycled. Early planning and wise choices will help you get the most out of your cover crops.
Plan ahead
You have better things to do in the fall than to start worrying about cover crops. Plan ahead. Know how many acres are needed to utilize all manure nutrients in the coming months. Order seed and be ready to go when the time is right.
Surface-applied manure is vulnerable to runoff, especially during frequent winter and spring snow melts. Avoid applying manure on heavy snow packs. Right-to-farm guidelines dictate that liquid manure should not be winter applied on slopes greater than 3 percent, and solid manures should not be applied on slopes greater than 6 percent. Select fields for spreading that do not slope to surface waters. If cover crops are not used or are not well-established, injecting or incorporating manure is your best bet.
Choose the right crop
Oats are sometimes used as a cover crop in the fall and need to be planted soon after silage harvest. Drilling oats improves germination and growth before frost. Oats that have eight to 10 weeks of growth under their belt before a killing frost can retain up to 75 pounds of nitrogen per acre. Because oats winter-kill, they are not a problem in the spring for no-till or minimum-tillage systems.
Another cover crop that is excellent at recycling nitrogen is oilseed radish. When planted before September 1, this crop can recycle 60 to 75 pounds of nitrogen per acre and reduce winter annual weeds. Oilseed radish winter-kills in Michigan and is easy to manage in the spring.
Cereal rye is an excellent cool-season grass for capturing excess nitrogen. Because rye overwinters, it can hold 25 to 50 pounds of nitrogen in the spring. It germinates at temperatures as low as 34 degrees, so it can be seeded later than oats, but the later the rye is planted, the less nitrogen will be recycled. Rye will grow later in the fall and begin growth earlier in the spring than wheat. It will also provide excellent winter pasture or a green-chop in the spring. However, its vigorous spring growth must be controlled with herbicides or tillage before it dries out the soil. Rye that is 9 to 12 inches tall can be controlled with 1 quart of glyphosate with ammonium sulfate per acre in the spring.
To seed harvested silage fields, spread rye or wheat with a bulk spreader either just before or just after the manure is applied, and then use a shallow tillage tool to incorporate both the manure and the cover crop seed. Rye and wheat are fairly forgiving of seeding depth, especially when cover, not yield, is the goal. Wheat, oats and rye should all be seeded at about 2 bushels per acre.
Slurry seeding—adding cover crop seed directly into the manure tank and then applying with a low-disturbance tillage tool—has shown excellent success in establishing cover crops at MSU.
Remember, cover crop seedings do not have to be perfect. Nutrient recovery and environmental protection—not high yields—are the goals. For more information on cover crops and slurry seeding, visit AnimalAgTeam.msu.edu or CoverCrops.msu.edu.
This article was published in the September 2008 issue of the Scoop. Click here to read the whole issue.