Top Crop Manager

Features Agronomy Seeding/Planting
Managing unseeded acres with annual cover crops


November 30, 1999
By Top Crop Manager

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With the potential for flooded acres carrying over into 2011, planning to manage those unseeded acres can help save nutrients, control weeds and even provide some cash flow. That is, as long as the land dries out enough to get some sort of cover crop on the field. “Flooding is not something that we like to talk about on the Prairies, but when it is an issue, there are options to go in with annual crops for green manuring or forage production,” says Glenn Friesen, forage specialist with Manitoba Agriculture and Rural Initiatives.

If farmers have land that is too wet to seed in the spring, Friesen says there are several options for farmers. He developed a MAFRI fact sheet in 2010 to help farmers deal with wet, unseeded acres. He provides the following information, based on that fact sheet.

Green manure improves soil fertility
For land that was flooded for a significant period of time, leaching or denitrification may have compromised nitrogen fertility. Friesen says farmers can take advantage of green manure crops to rebuild nitrogen fertility while also drying out the land. At the same time, green manure crops add organic matter to soil, and improve soil structure and drainage.

Friesen says the legume species used for green manure need to be picked carefully. Red clover is the best fit for quickly establishing on low-lying or saturated soils, and yellow sweet clover is a good option for coarse-textured and drier soils. Red clover and sweet clover are short-lived perennials used in many zero-till and organic production systems for improving soil conditions and adding nitrogen to the system.

Red clover establishes easily and tolerates wet and acidic soils, much more than alfalfa, explains Friesen. Although a perennial plant, it has the poorest winter hardiness level among the forage legumes; volunteers should be minimal after a few years of annual production. Single-cut red clover is also a better option than double-cut, as it tends to grow late in the season and not overwinter as well. Growing glyphosate-tolerant crops after forages also provides the ability to control volunteers.

Sweet clover is a biennial plant (lasting two years) that produces only forage in the year of seeding and forage and seed in the second year of growth; therefore, volunteers should also not be a concern if green manured in the fall of the seeding year. If planning on grazing the summer growth, it is important to choose low coumarin varieties of sweet clover, and to be cautious of the boat potential in red clover.

Friesen says some livestock producers have also had great success in seeding the two clovers together at a blend of 80 percent sweet clover and 20 percent red clover. For hay producers, the sweet clover can double hay yields produced by alfalfa and quicken dry-down. For annual croppers, the extra tonnage of sweet clover adds tremendous amounts of soil organic matter, improving soil tilth, drainage and fertility.

Looking at economics, Friesen says seed cost ranges from $1.30 to $3.50 per pound for common and Certified seed, resulting in an average seed cost of $20 per acre. The amount of nitrogen contributed by red clover can range from 30 to 50 lbs per acre and by sweet clover from 50 to 100 lbs per acre by full bloom, depending on the density of the stand, moisture availability, soil type, and the length of the growing season.

Green feed forage options
Friesen says another option once the land dries out enough for seeding is to plant annual crops such as barley or oats for green feed or swath grazing. They can provide high-energy feed for livestock in a short period of time. Barley and oats also can be used as summer pasture within four to six weeks of seeding.

“If moisture removal is the main objective, harvesting the crop as green feed, silage or swath grazing is recommended. Post-harvest regrowth can also provide late-season grazing,” explains Friesen. “Fertile soils can provide excellent late-season grazing well into October.”

Cleaning out the grain bins provides a good option for green feed forages. Friesen calls it polycropping, and describes it as seeding a mixture of wheat, barley, oats, millet, peas, hairy vetch and clovers for either green feed or swath grazing. A brassica crop such as turnip, radish or canola is usually included as these crops add a bit of natural “tillage” with their large roots. “Swath grazing is a good option because it is a low cost forage system, and cattle recycle the nutrients back on to the land,” says Friesen. “Some producers forget to include the value of urine in the nutrient equation for swath grazing. The urine is lost in the feedlot if that is where the cattle are fed.”

Economics with green feed forages is more complicated, as grain farmers will need a market for their forage or a swath-grazing neighbour. For both green manure and green feed forage options, economics also has to look at the costs of not having a crop on the land, such as weed control and lost nutrients. “On unseeded acres, the goal should be to cycle the nutrients and keep them there for next year,” explains Friesen. “Hopefully, using annual crops on unseeded acres can also generate some additional cash flow while drying out the soil and improving soil structure.”

For more information, go to MAFRI’s website at www.gov.mb.ca/agriculture/ and search for “Annual Crops to Manage Unseeded Acres.” The fact sheet includes detailed production information, variety selection guidelines, links to additional fact sheets and information on using warm season annual crops.


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