Top Crop Manager

Features Agronomy Corn
Air-drills suited for seeding corn

Don't worry about row spacing when planting grazing or silage corn with a solid seeding system.

November 19, 2007
By Top Crop Manager


Seeding corn with an air-drill or air-seeder usually raises questions around
row spacing. With most grain and table corn planted with a row planter on 15
to 30 inch row spacing, many grazing corn growers have wondered if seeding with
an air-drill would work, or if they should block off every other run in their
air-drill to simulate a row planter.

"The majority of grazing corn acres are sown with an air-drill or air-seeder.
It can be a bit intimidating if you are a first time grower, but after the first
year, they see that seeding and growing grazing corn is pretty easy," says
Rob Ripley, Monsanto seed and technology development representative in Saskatoon.
In fact, a recent survey by Monsanto found that 77 percent of its growers used
an air-seeder or air-drill for seeding grazing corn.

Over the last three to four years of grazing corn development, seeding rate
and stand establishment has moved away from an emphasis on row spacing to the
realization that targetted plant population is the critical factor. Ripley says
that any common row spacing will work with an air-seeder or an air-drill, and
that many growers use row spacings from seven to 12 inches quite successfully.
And, hitting the targetted plant population of 30,000 seeds per acre is crucial
in stand establishment.

For first time growers, the wide spacing between corn plants at emergence can
be disconcerting. On an eight inch row spacing with 30,000 seeds per acre, the
distance between kernels is approximately 26 inches, and at a 10 inch row spacing,
the seeds are 21 inches apart (see Table 1). That means there is usually only
one plant per 1.5 square feet.

Table 1. Distance between
corn kernels at different row widths and seeding rates.
Row width (inches) Final population assuming five percent
stand loss.
8 10 12 14 16 18 20 22 24 26 28 30
Kernels/ac Inches between kernels
26,000 30.2 24.1 20.1 17.2 15.1 13.4 12.1 11 10.1 9.3 8.6 8.0 24,700
28,000 28 22.4 18.7 16 14 12.4 11.2 10.2 9.3 8.6 8 7.5 26,600
30,000 26.1 20.9 17.4 14.9 13.1 11.6 10.5 9.5 8.7 8 7.5 7 28,500
32,000 24.5 19.6 16.3 14 12.3 10.9 9.8 8.9 8.2 7.5 7 6.5 30,400
34,000 23.1 18.5 15.4 13.2 11.5 10.3 9.2 8.4 7.7 7.1 6.6 6.2 32,300

"My experience with corn is that emergence is very slow and the stand
looks really thin, so you wonder whether it will work out or not. But once it
decides to go, it really takes off," says farmer Garry Thiel at Shellbrook,

Thiel grew Dekalb brand DKC27-12 grazing corn for the first time in 2004, and
sowed it with a Flexi-Coil 5000 air-drill and 3450 air-tank. He seeds on 12
inch row spacing and his opener has a four inch spread tip. His seed-placed
fertilizer rate was a blend of 30lb N, 30lb P, 5lb K and 10lb S. Another 10lb/ac
of liquid N was applied as the carrier for the first application of Roundup,
and 35 pounds of N was top dressed in mid-July.

A second Roundup application was used to clean up later flushes of weeds. "We
had so much rain and the corn canopy was slow to fill in, so we used a second
application to keep the weed competition down," explains Thiel.

Research showing air-drills work
At St. Brieux, Jason Kirsch with Bourgault Industries says that a research program
is comparing row planters to an air-drill. The 2003 results looked promising
but the 2004 results were inconclusive due to weather-related problems.

In the trials, conducted by PAMI, grazing corn was grown at St. Brieux and
Portage La Prairie. At St. Brieux in 2003, solid seeded (air-drill) grazing
corn DKC27-12 was compared to barley silage. Corn was seeded with a Bourgault
5725 air coulter drill and 5440 air-seeder. Corn was planted at 30,000 seeds
per acre. At Portage in 2003, solid seeded DKC27-12 hybrid corn was sown at
29,000 seeds per acre, while a John Deere 7000 row planter on 30 inch spacing
seeded 28,000 seeds per acre.

"In the 2003 trials, the Bourgault solid seeded corn showed a 17 percent
yield advantage over the row planter plot at the Portage site. It is just one
year of results, but it indicated good potential for solid seeding corn,"
explains Kirsch.

Calibrating the seeding rate
Each bag of Dekalb corn contains 80,000 seeds, and the weight is printed on
the bag since the weight varies slightly from bag to bag. To start the calibration,
choose the desired seeding rate, say 30,000 seeds per acre, and divide by the
number of seeds per bag. In this case, that gives you 0.375 bags per acre that
will be used. Then, multiply the bag weight by the number of bags per acre to
get the seeding rate in pounds per acre. For example, if the bag weighs 42 pounds,
then your seeding rate is 15.75lb/ac (0.375 bags per acre x 42lb per bag = 15.75lb/ac).

Ripley says that since there is some variation in the bag weight, simply take
an average weight when making the calculation. "Make sure you order all
the same seed size, as corn comes in different sizes. As well, there can be
up to 10 pounds difference between bags, so make sure to use an average weight
for each field."

From there, the pounds per acre seeding rate can be used to set up the air-drill.
How that is accomplished depends on the make and model of equipment. For example,
with the Flexi-Coil system, one of two different seed metering rollers can be
used to seed corn. Darryl Priel, CNH crop production specialist at Saskatoon
representing CaseIH, New Holland and Flexi-Coil, says that the fine-segmented
roller is recommended for seeding corn.

"Segmented meter sections are available at a low cost, reducing the change-over
investment for the producer who desires improved in-row spacing than what the
coarse roller provides," says Priel. It can handle most corn grades with
the exception of large, flat kernels. The segmented roller provides improved
in-row spacing (spacing between the seeds in the row) than the larger fluted
rollers in lower application rates. "The coarse meter roller, which is
recommended for crops like peas or beans, works better for large, flat seeds,
however, in-row spacing may be sacrificed," explains Priel.

On New Holland, Case IH and Flexi-Coil air-carts, setting the seeding rate
is then simply done with the monitor system, as is done with other crops. The
smart monitor/controller provides meter drive settings for mechanical meter
drive systems based on desired application rate, calibration volume and width
of implement. There are no rate charts required. The variable rate meter drive
system is easier, enter the desired rate in the monitor/controller, calibrate
and go. Refer to the owner's manual for complete instructions.

Kirsch says the Bourgault air-tank uses a metering auger to measure out the
seed. One tank has a double flight auger for seeding lower rates of seed, from
two pounds up to 150 pounds per acre. The second tank has a single flight auger
that can seed up to 250 pounds of product per acre. "Corn is usually metered
out through the double auger tank and it works just as well as with any other
product. To seed corn with a Bourgault air-seeder, the operator performs the
typical power calibration procedure to achieve the target seed rate," says

Ripley says that getting the targetted plant population goes a long way to
maximizing tonnage and feed value. He says that seeding at 30,000 seeds per
acre helps to ensure that the seeds are spaced evenly to allow each plant to
develop with minimal competition from neighbouring plants. Yes, the seeds will
be somewhat randomly spaced, but on average, the stand is fairly uniform.

"Over the last four years, we've seen good successes with air-drills and
air-seeders. As long as growers can achieve the targetted plant population with
fairly uniform plant spacing, they should be okay with an air system. Those
factors are much more important than row spacing," says Ripley. -30-