Drills are often used to place close-spaced crops such as cereal grains and soybeans. However, the charts provided by the drill manufacturer are often simply a starting point for obtaining the target seeding rate. Seed size, shape, coat, and density can all affect the actual seeding rate. Due to these factors, it is helpful for the grower to calibrate the drill yearly based on the seed they have purchased.

Follow these four steps to calibrate your seed drill

1. Establishing the seeded width

Determine the planting width of your drill. Be sure to measure the width of your drill. More than once, I’ve visited a grower, and they know that their drill covers 20 feet only to measure it, and it covers 19.25 feet. Remember to add half the row spacing to each side of the measurement if you pull the tape from the first disk opener to the last.

Alternatively, you can count the number of row units and then multiply that count by the row spacing to find the planted width. If you’re not 100% certain, be sure to measure the row spacing. I have walked up to a drill that the grower thought was on 7.5-inch spacing, only to find out it was on 7-inch spacing after we pulled a tape.

2. Determining a seeded distance

Find a place to pull the empty seed drill between 150 and 250 feet. I typically shoot for 200 feet for this test. Place a flag at the intended starting place and one at the finish mark. Put a piece of tape or other marker on the drive wheel of the seed drill. This next portion may be easier to do with assistance. With the tractor pull the seed drill at your intended operating speed 200 feet from the start flag to the finish flag while using the tape to count the number of revolutions of the tire. Complete this operation two to three times and take the average of the counted revolutions.

3. Stationary calibration setup

Please be sure to perform these steps carefully and safely.

With the tractor and drill attached securely together and on a level and firm surface, use a jack to elevate the drive wheel off of the ground enough to avoid contact when the wheel is rotated.

Two primary methods can be used to collect seed during the calibration. The first uses a tarp or multiple buckets placed under all row units to collect seed from the entire drill. The second method collects seed from only a portion of the drill and assumes an average seeding rate for the full width. The first method will be outlined below.

Load seed in the drill box, covering all seed cups for each drill section that needs to be calibrated. Some seed drills have seed rate adjustments for the left and right sides of the drill depending on the overall width. Be sure to calibrate both sides or all sections of the drill.

Disconnect the seed tubes from the bottom of the seed box.

Using the seed chart provided in the manufacturer operator manual or under the lid of the seed drill, set the meter opening to your targeted seeding rate.

4. Calibration

Turn the drive wheel to prime the seed cups. Hang a bucket or container under each seed cup with the disconnected seed tubes from step 3. If this is not possible, you can catch the seed from below the row-unit. Seed tube geometry can negatively impact seeding rate.

Rotate the drive wheel to the number of revolutions established in step 2.

Weigh the seed collected in each bucket using a balance that reads in grams or ounces. A digital kitchen or food scale will work. Remember to tare out the weight of the bucket. If one bucket has substantially more or less seed in it, then investigate and make adjustments or perform maintenance to that seed cup/metering system.

Sum all of the seed weights for each independent section of the drill.

The effective seeding rate can be determined by dividing the weight of the seed by the simulated planted area.

Seeding rate example:

Drill width: 10 ft

Simulated distance: 200 ft

Simulated area (ft²): 10 ft x 200 ft = 2000 ft²

Simulated area (acres): 2000 ft²/43560 ft² = 0.04591 acres

Total seed collected: 6.48 lbs

Estimated seeding rate by weight: 6.48 lbs / 0.04591 acres = 141.15 lbs/acre

Recommendations for seeding rate are often given in seed per acre. For example, wheat should fall from 1.3 million seeds/acre to 1.8 million seeds/acre when planted on time.

You will need the seed per pound (density) value on the seed tag to convert seeding rates by weight per acre to seeds per acre.

Assuming a seed density of 11,500 seed/lbs the seeding rate is calculated as follows:

141.15 lbs/acre x 11,500 seed/lbs =

1,623,176 seed/acre or 1.62 million seed/acre

If the desired seeding rate was not achieved, adjust the meter opening and repeat step 4.

Be sure to pay attention to germination values when settling on a final seeding rate.

Worksheets

Take a look at the calibration worksheet and record-keeping sheet to help you with your seed drill calibrations.

Seed Drill Calibration Worksheet

Seed Drill Calibration Record Keeping Sheet

If you have questions, please contact us at the N.C. Cooperative Extension, Bertie County Center, at (252)794-5317.