Cover crop mixtures are being encouraged more today than previous years, but the challenge is figuring what setting on the drill will drop the desired rate.

Calibrating your grain drill is the only way to avoid over- or under-seeding your fields.

We did this at a field day recently with annual ryegrass and crimson clover. The desired mixture was 10 pounds of each per acre, but when we looked at the grass seed chart on the grain drill (after we mixed the seed) the fastest setting for annual ryegrass was around 12 pounds per acre, but what would it be if we mixed it half and half with crimson clover.

Grain drill calibration is not too difficult and should only take you a half hour or so. What you will need is: a measuring wheel or tape, 2–4 containers, a scale that measures in hundredths of pounds, calculator, pen and paper.

• Start by calculating the width of your drill. Count the number of openers and multiply by the disk spacing.
Ex. 24 openers x 7.5” spacing = 180” or 15.0’.

• Divide 43,560 by 20 to get the number of square feet in a 1/20th of an acre.
Ex. 43,560/20=2,178.

• In order to know how far to drive to collect seed from the drill divide 2,178 (1/20th of an acre) by the width of the drill in feet.
Ex. 2,178/15.0´= 145.2 feet.

• Now that you know how far to drive, measure out the distance and flag or mark the starting and stopping point.

Mark with chalk, use valve stem

• Next mark the tire with chalk (or use the valve stem), do this in the field preferably with the drill in the ground to account for slip, count the number of drive tire revolutions in the measured distance.
Ex. We counted 19 revolutions on the drive wheel in 145.2 feet.

• Next, park the drill, either jack up the drive tire or block up the drive wheel so you can turn it by hand.

• Weigh one container and write down its weight or tare the scale.
Ex. Empty container weight = 1 pound.

• Remove ¼ of the seed tubes from the disk openers and place the ends of them in buckets to collect the seed.
Ex. In our case this was 6 of the 24 seed tubes, you can do 2 seed meters side by side into one container and use 3 containers to catch 6 tubes.

• Put seed in the drill, you only need enough to cover the rows that you are collecting from.

• Turn the drive wheel a few times until the seed fills the meter and comes out the tube.

• Empty your containers.

• Turn the drive wheel the number of turns needed to go the distance measured earlier equaling 1/20th of an acre. Ex. 19 turns.

• Combine all the seed together in the one bucket and weigh.
Ex. 1.20 pounds — 1.00 pounds = 0.20 pounds of seed.

• Then multiply the amount of seed collected by 4 since you only collected from 1/4th of the drill.
Ex. 0.20 X 4=0.80 pounds.

• Then multiply that number by 20 since you only did 1/20^th of an acre.
Ex. 0.80 x 20=16.0 pounds per acre (this is less than our desired 20 pounds per acre, but sufficient enough to plant the field). That final number is the pounds of seed that will be planted in an acre.

• Repeat this process 2 more times and see that it is consistent.

What we should have done was to look at the seed chart first then put the annual ryegrass in the main box and the crimson clover in the small seed box and calibrate them separately to achieve the desired rate of each.

You can use this method for small grains, grass seed, soybeans or anything else you plant with your grain drill.

Write down this information in your owner’s manual so next season you will know what setting you used and if you want to calibrate your drill again with another crops you will already have the distance measured out.

For more information on drill calibration go to http://www.ces.purdue.edu/extmedia/ABE/ABE-126-W.pdf.