Prep for Perfect Planting

February 10, 2012 06:39 PM

Picket-fence corn requires planter parts to work in sync

The basic design of every planter is the same, whether it’s a shiny new GPS-guided, vacuum-metered 36-row megaplanter or an acre-worn eight-row planter with finger-pickup units and bent marker arms. Planters are designed to meter and place seed.

Equipment manufacturers and farmers have the metering side down to an exact science. Well-maintained seed units, whether vacuum or finger- pickup style, can drop seeds with
robotic accuracy and set the stage for picket-fence stands.

But many farmers still don’t achieve those fabled stands. Skips and doubles mar their final population and reduce yield. Even more insidious are yield reductions from stands of corn that initially appear perfect. Even though there’s a stalk every 6.5" during the growing season, random stalks at harvest can be barren.

One is not like the other. "A seed meter can singulate a picket-fence stand to the top of the seed tube, but poor seed placement in the furrow can lead to erratic germination and emergence," explains Dustin Blunier, marketing communications manager for Precision Planting. "We like to see all plants in a field germinate and emerge within 36 hours of each other. Plants that emerge a day or two behind become weeds that absorb nutrients and moisture. They often end up barren or producing nubbin ears."

Blunier cites research by Robert Nielsen at Purdue University that indicates erratic germination and emergence can reduce final yields in corn by as much as 10%.

"It may take $400 per row to go through an older 12-row planter and replace worn disk openers, gauge wheel arms and components other than the seed meter," Blunier says. "That’s $4,800 in parts. If you plant 500 acres of corn that maintenance costs $9.60 per acre. At today’s prices, that’s less than 2 bu. of corn spent to maintain the planter to potentially gain 20 bu. at harvest, if the corn yields 200 bu. per acre."

Doug Toepper, a product specialist with John Deere Seeding Group, says the interactions between disk openers, gauge wheels, seed tubes and closing wheel assemblies are critical to accurate seed placement.

"A planter is a system," he says. "All the pieces have to be matched and working properly to get optimum planting results."

Disk openers start the placement process by creating a precisely engineered seed furrow. If the contact area where the leading edges of disk openers touch is too small because the disks are worn or out of adjustment, or if there’s a gap between the disk openers, loose soil falls into the bottom of the seed furrow and positions some seeds shallower than others. Uneven depth of seed placement is a major factor in erratic seedling emergence.

"Even ‘good’ disk openers that aren’t worn smaller than 14½" can be out of adjustment and affect seed placement," Toepper says. "If the farmer shimmed them to get the proper 2" to 2½" of contact at the front of the disks but put more shims on one side of the row unit than the other, it can off-center the disks and one of them can rub on the side of the seed tube. That will eventually wear a hole in the seed tube, and anything that causes a seed to tumble or bounce as it leaves the tube can affect spacing in the furrow."

A special relationship. Tom Evans, vice president of sales for Great Plains Manufacturing, says the relationship between disk openers and gauge wheel tires deserves attention.

"If the soil is damp and there’s a gap between disk openers and gauge wheel tires, wet soil will stick to the disk opener, peel off inside the gauge wheel rim and eventually plug the gauge wheel so it can’t turn," Evans says. "If the soil is dry, it’s even worse because it affects seed placement and potential yield. Any gap between the gauge wheel tire and the disk opener allows the gauge wheel tire to kick dry soil into the bottom of the furrow."

In that situation, some seeds germinate quickly in damp soil, while other seeds sit higher and dryer on soil allowed into the furrow by the gap between the gauge wheel tire and disk opener. Even if a rain germinates them all at the same time, shallower seeds will emerge first and potentially dominate the plants on either side.

Proper adjustment of gauge wheel tires against disk openers can be difficult if tires are worn. Most gauge wheel tires have a flared lip designed to press lightly against disk openers to "squeegee" soil away. Over time, the rubber edges of gauge wheel tires wear and become less effective.

Gauge wheel arms also affect tire-to-disk opener contact. After pounding over thousands of acres, arms often develop wear at the pivot point where they mount to the row unit or get bent by contact with rocks and other field obstructions.

Planter manufacturers offer replacement kits to rebuild worn gauge wheel arm mounting pivots. Arms bent by rocks should be replaced to make sure gauge wheel rims were not also damaged or bent by impact.

Precise planting isn’t finished once seeds are evenly placed in the seed furrow. Toepper, who farms with his family, recently rebuilt all of the closing wheel frames on his John Deere 7000 planter to ensure optimum germination and emergence.

"We were having trouble closing the seed furrow," he notes. "Over time, the closing wheel frames wear, making it difficult to keep them centered over the seed furrow. The angle of the closing wheels is designed to collapse the sidewall of the seed furrow and gently squeeze soil around the seeds without packing soil over the top of them.

"If the closing wheel assembly is worn or bent so that one of the closing wheels runs right over the furrow, it makes it tougher for those seeds to emerge through that packed soil," Toepper says. "If your closing wheels are working correctly, the soil right over the seeds is loose, but if you dig down, the soil around the seeds is firmed against them for good seed-to-soil contact, quick germination and even emergence."

Toepper says nearly any planter has the potential to create picket-fence stands of corn. "New planters can plant poorly, and old planters can plant great," he says. "It all depends on how they’re maintained and adjusted."

p14 Prep for Perfect Planting
The purpose of a row cleaner is to clear residue from the seed furrow, which helps reduce autotoxicity.

Defending Corn Against Itself

Allelopathy is a biological phenomenon where chemicals produced or derived from one plant affect the growth of another plant. Autotoxicity occurs when the offending chemicals come from plants of the same species. Autotoxicity is a form of allelopathy that kills or stunts corn seedlings exposed to corn residues from the preceding year. Planter-mounted row cleaners are a potential "cure" for autotoxicity.

"If your final stand of continuous corn has a lot of skips, do some digging to figure out if it’s because the planter didn’t meter or place the seeds accurately, or if the seeds got placed in or under a pocket of residue from last year’s crop," says Tom Evans, vice president of sales for Great Plains Manufacturing. "Even if they emerged, seedlings associated with residue may be weak and yellow and never produce an ear."

Evans says properly adjusted tined row cleaners reduce autotoxicity by clearing most residue from the seed furrow area.

Farm Journal Field Agronomist Ken Ferrie says his rule of thumb for adjusting row cleaners is that only one-third of the row cleaners on a planter should be turning at any time.

Properly adjusted row cleaners won’t leave a perfectly black, residue-free path for planting, but they’ll reduce dense pockets and patches of residue that could make young seedlings gag.


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