GHGMP Project Reports by Region

Proper crop rotations sprout range of benefits

Rotating crops isn't a new concept, but it takes planning to manage the right sequence for today's farms

Diverse crop rotations that include pulse crops (pea and lentil), oilseeds, winter cereals and warm-season forages can provide a range of dryland and irrigation farming benefits, says a southern Alberta soil conservation specialists.

Good economics, improved soil conservation, effective, lower-cost weed control and reduced greenhouse gas emissions are among the potential advantages of managing a proper rotation, says Don Wentz, an agronomist with Alberta's Reduced Tillage LINKAGES (RTL) based in Lethbridge. RTL crop rotation demonstrations are partially funded by the federal Greenhouse Gas Mitigation Program for Canadian Agriculture (GHGMP).

"With increased interest in zero tillage and continuous cropping we're finding a proper crop sequence is important to making the systems work," says Wentz. "Some people can get by with wheat on wheat or canola on canola for awhile, but monoculture systems aren't sustainable."

Monoculture increases the risk for crop diseases, insect pests and even tougher weed control issues. "The question is why put yourself in a situation where you could develop problems like sclerotinia in canola or root rot in cereals," says Wentz.

While pulse crops and winter cereals, for example, have been around for years, their potential benefit in a zero-till rotation may not be widely understood. And a fairly new Prairie crop category, warm-season forages, which includes crops such as proso millet and sorghum-sudan grass, can provide short-term pasture and hay as well as important ground cover on land at risk to wind erosion.

Environmental benefits

A diversified crop rotation not only provides a good return, but also helps conserve soil and reduce greenhouse gas emissions. Zero and reduced-tillage systems, for example, help minimize the amount of carbon dioxide released from the soil. At the same time, using either chemfallow or alternate crops for ground cover instead of conventional summerfallow reduces the use of fossil fuels and retains a protective layer of crop residue. The crops also capture carbon dioxide from the atmosphere, which is stored as carbon in plant tissue and the soil.

More producers find that including a pulse crop in rotation provides several benefits, says Wentz. "Dryland peas, for example, grow well, the commodity is quite marketable and they benefit subsequent crops in rotation." The nitrogen-fixing legumes help reduce fertilizer cost not only in the pea year, but also in subsequent crop years.

Producers need to think about where peas fit in rotation, says Wentz. Points to consider include the fact that peas and some oilseeds are host to similar diseases such as sclerotina, and neither peas nor oilseeds produce large amounts of crop residue. "You may not want to follow a rotation that includes back-to-back mustard and peas with a fallow or chemfallow year because of the low crop residue," he says. A four-year rotation sequence such as oilseed/cereal/pulse/cereal may have a good fit in the Brown Soil Zone.

A strip farming rotation also helps conserve soil in areas prone to erosion. This technique involves creating 40 to 80 acre crop strips running north and south. A typical rotation starting on the west side of a field might include 40 acres of wheat, 40 acres of peas, 40 acres of chemfallow and 40 acres of canola. "The next year you move the sequence over one so the wheat is on pea stubble, and the peas go on the chemfallow and so on," says Wentz. "It's an effective way to protect the soil and optimize yields."

Different forages

Warm-season forages are being tried on an experimental basis as an alternative to fallow. Crops being demonstrated include proso millet, German millet, Siberian millet and sorghum-sudan grass. These crops are classed as C4 crops, referring to their method of photosynthesis, which allows them to sequester more carbon dioxide and grow quickly under warm, dry conditions. They need a soil temperature of at least 10 C to germinate.

Wentz sees warm-season forages as short-season crops providing good ground cover. Seeded in mid-June, the forage or hay crop could be harvested by early to mid-August. "In the fallow year, a producer could seed a warm-season forage to provide good ground cover," he says. "The forages would work particularly well if they followed low-residue crops such as sunflower and some oilseeds."

In one project, 15 and 20 acre fields of Siberan millet and sorghum-sudan grass, respectively, were seeded into well-fertilized durum stubble. The fields were silaged in late August with a yield of nearly 2 tonnes per acre dry matter of sorghum-sudan grass and about 1.5 tonnes per acre dry matter of millet. The sorghum-sudan grass had a crude protein of 17 percent, compared to typical green feed oats at about 15 percent.

The crops could also be swath grazed, and under irrigation, could be seeded as a second crop after winter triticale is silaged in late June.

Weed strategy

A well-planned rotation can also help control weeds and reduce herbicide costs, says Wentz. "When you get a field clean, the crop rotation can help keep it clean," he says. "The three-stage strategy is known as sanitation, rotation, and competition. With weeds under control use rotation and competition to keep it clean."

Winter wheat, for example, is an excellent crop for helping control wild oats. As a strong competitor, the winter cereal has enabled some producers to eliminate a $15 per acre wild oat herbicide.

Along with the competition factor, timing is also important, says Wentz. Growing different crops with different seeding dates changes the herbicide schedule and "keeps weeds off balance." The changing schedule means more effective weed control, and the crop mix also allows for herbicide rotation.

"A rotation such as canola/winter wheat/peas/spring wheat/canola provides several benefits and can also be profitable," says Wentz. "While it sounds easy, trying to schedule four or five crops in proper sequence over several thousand acres takes a lot of management. It's a complex task.

"Still, more producers are realizing the benefit of a proper rotation. It has to make economic sense, but as stewards of the land, producers also want to protect and enhance soil as a resource and the environment."


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