The Rotation Equation: Where should sunflower fit?
Perhaps of all crops grown in the Plains, sunflower requires the most strategy in choosing its place within a crop rotation.
Sunflower grows well under dry conditions. It joins safflower as one of the most deeply-rooted crops, with a root system that can dig down 5 to 7’. Thus, it is one of the most adept crops at utilizing subsoil moisture. For example, while proso millet will extract about 4” of water from the top 3’ of soil, sunflower extracts about 7.5” from the 6’ profile. As well, sunflower is second only to peas in water use efficiency, and one of the best broadleaf crops at converting water to seed yield, according to research at the USDA-ARS Northern Great Plains Research Lab in Mandan, ND.
There’s a double-edged sword to sunflower’s ability to use water, however. Sunflower’s advantage in extracting more water from the soil than other crops also means it depletes the soil of water available for the subsequent crop. In crop sequence experiments at Mandan, sunflower depleted the largest amount of soil water, and dry pea and lentil the least amount.
Steve Merrill, soil scientist at Mandan, says that crops which use less soil water generally:
A number of crop scientists and studies suggest a minimum four-year rotation cycle that includes sunflower. For example, one Canadian research study reported the success of a spring wheat-dry pea-barley-sunflower rotation. The broadleaf crops helped boost yield of the following small grains, and alternating legumes and oilseed crops helped avoid buildup of plant diseases.
“One rotation I like for North Dakota is sunflower, barley, peas, and wheat, then back to sunflower,” says Duane Berglund, NDSU extension agronomist. “The challenge in very dry conditions is what you should plant following ‘flowers. One idea might be fallow, followed by winter wheat. That’s something to consider, particularly in South Dakota or southwest N.D.”
An annual forage crop for hay might also work following sunflower. “And when it starts getting dry, you cut it so that field has a chance for moisture recharge,” says Berglund. “Any short-season crop after sunflower that isn’t deep-rooted may work.” No-till is a factor in the equation. “The no-till practice can be equally compared with fallow, generally giving a two inch advantage in soil moisture over continuous cropping with conventional tillage,” says Berglund.
The cycle-of-four crop rotation has been shown to be favorable in drier climates, where three crops are combined with fallow. Winter wheat-corn-sunflower-fallow was one of the more productive rotations in a crop rotation study at Akron, Colo.
Some producers are considering shorter rotations, such as winter wheat-sunflower-fallow. However, some crop scientists say a better approach might be to rotate two three-year rotations, such as winter wheat-sunflower-fallow with winter wheat-corn-fallow. This approach has proven successful in western South Dakota; diseases in sunflower are minimized by the crop interval of six years, whereas the synergistic effect of sunflower on yield of following crops is retained.
At Colby, Kansas, research suggests that a winter wheat-corn-sunflower-grain sorghum-fallow rotation is worth considering. With soil moisture likely to be somewhat depleted after corn, sunflower has shown the potential to extract subsoil water that is unavailable to either corn or grain sorghum, which favors sunflower after corn.
According to the research at Colby, grain sorghum required the least amount of available soil moisture to maintain small year-to-year yield variation, and produced high amounts of crop residue. This suggests that grain sorghum follow sunflower as the last crop before seeding wheat, not only to provide another cash crop, but also to provide additional crop residue cover during the extended fallow period. Other suggested sunflower rotations for the High Plains include:
For more information, see the “Irrigation/Water Use” section of the Sunflower Magazine archives. Go to www.sunflowernsa.com, click on “The Sunflower Magazine,” and then “the archives.” – Tracy Sayler
Fast ’Flower Fact: An acre of sunflower will produce about 150 pounds of seed, on average, for every inch of water use after the first seven inches.
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