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Planting, Seeding & Spraying EquipmentGrain Drill Calibration
Chart settings get you close, but only a calibration test tells you how much seed your drill actually puts out. This guide covers how to do it safely and repeat it for each seed lot.
Key points
- Calibrate with the seed you will actually plant.
- Spin the drive wheel a measured amount, weigh the catch and compare to your target.
- Adjust in small steps and write down every change.
- Recheck in the field by comparing seed used with acres covered.
Why does a grain drill need to be calibrated?
Seed size, shape, coating, moisture and even how full the box is can change how a drill meters. A chart in the manual assumes typical seed. Your seed lot may not be typical.
Calibration saves money and protects your stand. Too heavy and you waste seed and crowd plants. Too light and you get thin spots where weeds move in. The test takes a short time compared to what an error costs across a whole field.
Seed sources vary too. Treated, coated, cleaned and bagged seed can all meter differently, and a lot that looks like last year's can behave in a new way. Fluffy native grass seed and small round clover seed are two good examples of seed that act nothing alike in the same box.
What do you need to calibrate a drill?
Gather your tools before you start. You will need a clean tarp or catch trays, a scale that suits the weight of the seed you catch, a calculator, a tape measure, a notepad and the manual with its rate chart. Have the seed you will actually plant, not a substitute.
Check that the drill is clean, the metering parts turn freely and every seed cup or flute is set the same. Jack or block the drill so the drive wheel can spin, using the lifting and blocking points the manual specifies.
- Catch containers or tarp
- Scale
- Tape measure
- Calculator and notepad
- Manual with rate chart and the real seed lot
How do you catch and measure seed?
Most drills calibrate by turning the drive wheel a set number of revolutions or by driving a measured distance. Follow your manual for the preferred method for your model. Measure the wheel circumference or use the stated figure to work out the ground distance covered.
Fill the box enough to prime the meters, spin until seed flows from every tube, then empty the catch and start the measured test. Weigh the seed caught and compare it to the target for the area that distance covers.
Keep your catch trays level and shielded from wind, since light seed can blow out of the tray. Write down the revolutions, the weight caught and the setting for each test. A simple table of those three numbers will save you from repeating work next season.
- Prime the meters until all tubes are flowing
- Empty the catch and run the measured test
- Weigh the seed and record the result
- Repeat at least once to confirm
How do you adjust the rate after the test?
If you caught too much, reduce the setting and test again. If too little, increase it and test again. Move in small steps and write every change down. Never make several changes at once, or you will not know what worked.
Compare weight per tube too. If one tube delivers noticeably more or less than the others, look for a worn cup, partly blocked tube or a loose setting on that run.
Remember that field conditions such as slope, soft ground and wheel slip can change how far the drive wheel really travels. If you plant on a steep hillside or in loose soil, expect the field result to differ a little from the stand test, and plan a field check to see.
How do you check the rate in the field?
Even a good calibration can drift. Check the number of acres covered against the seed used from the box. Mark the starting seed level, plant a known area, and then see how much seed you used.
Dig behind the drill at a few spots and count seeds in a measured length of row. Compare it with your target plant population from extension guidance for your crop and region.
On a 30-acre hay field, an error in seed rate of even a modest amount adds up quickly across the whole field, so a field check partway through the first load is time well spent.
What common calibration mistakes should you avoid?
Using the wrong seed, skipping the second test, forgetting to prime the meters and not accounting for field speed changes are the biggest errors. Another is trusting an old setting from last year without testing the new seed lot.
Plan to recalibrate for each seed type and lot, after any repairs to metering parts, and when you notice stand differences between fields.
- Not priming meters before the catch test
- Using last year's setting on this year's seed
- Ignoring one low or high tube
- Testing only once
What should you do when the box is nearly empty?
Metering can change when the seed level gets low, especially on light seed that bridges or packs. Stir or agitate if your drill allows, and keep an eye on the last few tubes to see that all are still flowing.
At the end of the job, empty the box, clear the meters and brush out remaining seed. Leftover seed attracts rodents and holds moisture, and old treated seed should be handled and stored as the label directs.
Sources and further reading
- Kansas State University Research and Extension
- University of Nebraska-Lincoln Extension
- Purdue Extension
- American Society of Agricultural and Biological Engineers (ASABE)
Organization homepages are linked so you can search them for current guidance on this topic.