Standard grain drills are very reliable and do a good job of sowing closely spaced seeds, provided time has been taken to effectively calibrate the drill. Unfortunately, this step is all too often omitted during the rush to complete the sowing process.

Simply setting the grain drill on the same sprocket combination or meter setting used last year, or adjusting to the grain drill’s factory-recommended seed chart, seldom results in desired seed output.

Seed type, size, variety, weight, germination rate, soil type and other factors will all influence the final seeding rate and will cause variation among factory-recommended seed charts.

While there are many ways to effectively calibrate your grain drill meter, here are a couple of methods utilized by growers across North America. Both methods are sometimes preferred because they allow you to calibrate your grain drill in a stationary setting versus an actual field operation.

Method 1

1. Before adjusting your grain drill to factory-recommended seeding rates, be certain that each meter is in good working order and tightened onto the seed drive shaft to prevent unnecessary movement within each individual seed cup.

All of the meter rolls should function the same, and you should verify that they can be completely closed or completely opened in unison within each seed cup.

2. If your meter is equipped with an adjustable seed gate, set the gate on the correct position recommended by the factory. This will vary with seed type and size. The larger the seed, the wider the seed gate should be positioned away from the meter roll.

3. Proceed to set the grain drill utilizing the recommended factory seed chart settings. This will provide you with a good starting point but will probably be slightly heavy or light when compared to your desired seeding rate.

4. Do not fill the seed box completely. Provide just enough seed to cover the cups. Captured seed will be reused.

5. For this example, we will utilize a drill working width of 10 feet for our calculations (number of openers x spacing in inches = width). If we have 16 openers at 7.5-inch spacing between openers, our drill width is 10 feet wide.

6. To calculate the area sown, use the formula:

Length of travel (feet) x width of drill (feet) = square feet covered / 43,560 square feet per acre = fraction of an acre

In this example, it would be 0.046 acres. Generally, 100 or 200 feet of travel is adequate for this calculation.

7. Measure the outside circumference of your grain drill’s drive wheel and calculate the number of tire revolutions required for the drill to travel a distance of 200 feet in length.

A piece of tape or other mark on the drive wheel will provide a good reference point to count the exact number of revolutions required to travel the 200-foot length (distance traveled / wheel circumference in feet = 200 ft. / 2.75 ft.).

8. With the drill raised and out of the ground, rotate the drive wheel of each section until you begin to see seed fall from the opener.

9. Tie a bag or other container onto each of the cups to collect seed.

10. Turn the drive wheel tire the appropriate number of revolutions to equal the predetermined 200 feet of travel.

11. Empty the seed caught in each bag into one container and weigh the total amount of seed obtained from the seed meters.

12. Divide the total meter seed weight by the sown area (weight of collected seed in pounds / 0.046 acres from example).

13. Compare the results of the calculation to your desired rate. To fine-tune your seed rate, open or close the seed meters until the desired rate is obtained.

Method 2

Another stationary method is to use a balance scale. This method is fast and provides a quick reference for seed calibration rates. As pointed out above, you must have a specific distance of known travel to provide an accurate sample. The following travel distances are for a few popular grain drill row spacings.

• 6 inches – 290 feet
• 7.5 inches – 232 feet
• 10 inches – 174 feet
• 15 inches – 116 feet

1. Fasten a bag or container to an individual seed cup.

2. Measure the circumference of the drive tire for the grain drill.

3. Calculate the number of drive tire revolutions required for the drill to travel the respective number of feet, based on the opener spacing of the drill (as shown above).

4. Empty the captured seed from the seed cup into the scale canister.

5. Level the seed in the canister for an accurate weight.

6. Support the scale by the ring, with your finger holding the ring, or tie a cord to the ring and fasten to a stationary point.

7. Slide the weight on the beam of the scale until the level bubble is centered.

8. Read the pounds per acre at the center mark of the weight slide.

The cost for a gravity scale for seed calibration is minimal and can definitely pay for itself in reassurance and peace of mind.

Hopefully, this exercise in drill calibration will be helpful to you and provide confidence that overseeding and underseeding with your grain drill can be reduced so overall crop stands and yields will be improved. Take time to calibrate your grain drill.  FG

Gary Johnson is the product manager for Kuhn Krause.