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Minnesotans Examine Legumes Interseeded in Sunflower, Corn

Sunday, March 1, 1998
filed under: Planting Systems

Hairy vetch sounds more like some-thing you’d find when cleaning out a kitchen sink drain than like something that could benefit your farming operation.

A group of northwestern Minnesota producers are discovering, however, that hairy vetch has potential to help protect their soils, reduce fertilizer and herbicide inputs, and improve overall crop produc-tivity. During the past couple years, more than a dozen Red Lake County farmers have interseeded this particular legume into plots (averaging 10 acres in size) within their commercial sunflower and corn fields.

Two years’ results indicate that signifi-cant vetch residue can be produced without an adverse effect on sunflower or corn yields. In 1996, for example, sunflower plots interseeded with hairy vetch averaged 1,572 pounds of seed per acre, while adjacent sunflower without vetch averaged 1,501 pounds. In 1997, the yields averaged 1,447 and 1,472 pounds, respectively.

The Minnesota hairy vetch project — which is part of the Minnesota Department of Agriculture’s Energy and Sustainable Agriculture Program — stemmed from principal investigator Hans Kandel’s prior experience in North Dakota with the interseeding of legumes in row crops. Kandel, who is Red Lake County extension educator for the Minnesota Extension Service, worked with several interseeded legumes while employed by North Dakota State University. As in the Minnesota trials, the major focus of the NDSU interseeding research was to try to control erosion following harvest while increasing soil nitrogen and organic matter — all without negatively impacting yields of the main crop (e.g., sunflower).

The Minnesota project — which will continue in 1998 — has used vetch because it is a fast-growing plant. In previous research, it produced the greatest biomass under low light conditions, as compared to other selected legumes such as sweetclover, alfalfa, black lentil and snail medic. In addition to its interseed benefits in a crop like sunflower, vetch also can be very useful as a green plow-down, as a grazing plant — and as a weed suppressor, if given a head start over germinating weeds.

Hairy vetch, one of several within the vetch family, is a viny, weak-stemmed legume that will grow to a three-foot height before falling over — but then continues to grow while on the ground. With an individual stem easily stretching to a length of four feet or more, a solid-seeded vetch plot takes on the appearance of a green, leafy, tangled mat. If there is something nearby to climb — such as a sunflower or corn stalk, the vetch will quickly begin doing so. Hairy vetch does best in moist, well-drained soils with a pH between 6 and 7, but it will tolerate drier conditions and a pH range of from 5 to 8.

As a legume, vetch has the ability to fix atmospheric nitrogen. “In the case of our test plots, where the farmers were fertiliz-ing a field for sunflower — or especially for corn, an interseeded vetch crop will use free nutrients early in the season,” report Kandel and his assistant, Joseph Schafer. “By the end of the season, however, most of the nitrogen has been used by the main crop, and the vetch is forced to fix nitrogen. In our plots, the vetch was always green and the roots always had nodules formed in late summer and fall, indicating it was producing its own nitrogen.”

Timing of an interseeded crop is critical, as the farmer wants to produce as much growth as possible without imposing a negative effect on the cash crop’s yield. That means letting the cash crop get a head start — but not too wide a gap. In the Red Lake County plots, the vetch was spread at a rate of about 20 pounds per acre when the sunflower and corn were between four to 10 inches tall. The legume was incorporated during the final cultivation pass. Suggested incorpor-ation depth is between one-half to one inch — but in no case deeper than two inches.

“Vetch is a fairly large-seeded legume, and it can germinate in some poor seedbed conditions,” Kandel and Schafer relate. Though the seeds usually germinate well, “the young plant is very tender for the first two weeks and is very susceptible to hot sun and dry winds if the soil is too dry.” Ironically, the plot producing the greatest quantity of hairy vetch in 1997 (more than 2,000 pounds per acre) was not incor-porated. “Not incorporating the seed is risky, though,” Kandel advises, “not only because of moisture and seedling vigor concerns; but because the seed is exposed to other detrimental influences while on the soil surface.”

Good weed control is important when growing this legume by itself, since vetch does not compete well with weed growth when the vetch is small. If a field is not particularly clean, a fall seeding date is preferrable to a late spring planting, Kandel suggests. “When vetch is seeded in the fall, it will overwinter like winter wheat and is growing as soon as the soil surface is warm enough to break dormancy in spring,” he observes. “By the time the first weeds are emerging, the vetch has already formed a loose mat on the soil — and will soon be thick enough to stop weed development.

“When seeding vetch, as an interseeded crop or on its own, it is beneficial to try to anticipate the weed pressure in the selected field. If there will be heavy weeds, some type of control plus earlier vetch seeding is called for.” — Don Lilleboe
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