NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665
March 30, 2000
Fast emergence and uniform stands are keys to peak grain yields. And starting off with seeds planted at a uniform depth in moist soil is an essential first step toward a uniform stand of grain that is vigorous and highly competitive, says a North Dakota State University agricultural engineer.
"If spring moisture continues to be limited, tillage should be avoided," says Vern Hofman of the NDSU Extension Service. "Tillage dries the soil, and the resulting variable germination will reduce the chance to get a good stand. Direct seeding into an undisturbed seedbed may be the best method to get a vigorous stand if dry conditions persist."
In general, the best planting depth for small grains is between 1 and 2 inches. Planting that close to the soil surface is desirable for quick emergence and to establish a stand to compete against weeds. Direct seeding allows seed placement in moist soil so if dry weather continues, roots will be established in moist soil even though soil near the surface may dry out. Planting deeper than 2 inches places seed in cooler soil, increases the time for plants to emerge and gives weeds a head start. "A thick and uniform stand may be one of the best and most economical methods of controlling weeds," Hofman says.
A uniform seeding depth is difficult to maintain with older double-disc press drills, Hofman notes. Disc openers are free to move to almost any depth. These drills almost always require a pre-seeding tillage operation so they can penetrate the soil -- an operation that further dries the soil.
With double-disc press drills, spring down-pressure pushes the opener into the soil. The only thing controlling the depth is the firmness of the soil. Hofman says the press wheels are designed to carry the weight of the drill and firm the soil over the seed, not control the depth of the disc openers. Depth bands are available and will help maintain uniform depth, but they are seldom used because they reduce residue clearance. "Speed also affects planting depth," Hofman says. "As speeds increase, it's even more difficult to control seed depth with older press drills."
Hofman notes that a warm seedbed also enhances seedling emergence. That may be a challenge in no-till systems where soil-conserving residue keeps the soil cooler. "However, the seed opener on a drill disturbs the soil which helps warm up the area where seed is planted," he says. "Also, shallow planting permitted by new planters helps reduce the effect of cool soils. Direct seeding in dry years may be the best for establishing a good stand."
"Newer equipment has solved many of the problems associated with seed placement as depth control equipment has been incorporated into machine designs," Hofman says. "That equipment allows producers to place seed more precisely at shallower depths."
The best units for depth control have a gauge wheel directly alongside the opener. Their main drawback is reduced trash clearance, Hofman says. The next best unit has gauge wheels mounted behind the opener and connected to the opener framework. Some gauge wheels mounted in this configuration are small in diameter, narrow and have difficulty maintaining proper depth because they sink into soft soil. A wider and larger diameter press wheel will usually provide better depth control for an even stand, he says.
Air seeders usually contain load-carrying wheels in front of the seeder and press wheels behind. Some are stretched out more than others for trash clearance which causes them to lose some depth control. "Greater distances between seed openers and gauge wheels may reduce depth control accuracy," Hofman says. "Newer air seeders have improved considerably in depth control compared to units that were introduced 10 or 15 years ago."
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Source: Vern Hofman (701) 231-7240
Editor: Tom Jirik (701) 231-9629