Soybean seed size effects planter or drill seeding rates. The only way to ensure your seed drop is what you are targeting is to calibrate. There are numerous methods to calibrate a grain drill or planter. One method is described below, but at end of this article another method is available as a link.

This method of calibration method is preferred by Ron Hoover, On-Farm Research Coordinator at Penn State Extension. Although these calibrations could be done by jacking the planter or drill and spinning drive wheels/shafts a given number of turns to simulate a fraction of an acre, we feel it would be best if the seed drop was measured while the equipment is being pulled to include the “bounce factor” that alters seed flow and drop during field operation.

Unneeded planter units can be easily disengaged (or not filled) during calibration. Likewise, duct tape and cardboard come in handy to create “seed dams” to prevent seed from filling unneeded holes in a grain drill seed box.

Note # 1: Seed count is the needed information, not seed weights!

Note # 2: If calibration is being done days in advance of when the field will be planted, record all the details for correct set-up at planting time: planter or drill sprocket combinations or gearbox setting, drill seedbox gate settings, etc.

I have found the following method of calibrating soybean seed drop to be desirable for many reasons:

  1. It is quickly and easily completed.
  2. The extra materials needed are kept to a minimum: 35 feet or more of ½ inch or larger soft rope, a measuring tape, a roll of duct tape, a small pail, and a calculator.
  3. Running the drill at field speed should improve accuracy.
  4. With a second person helping to pick-up and count seed, a new run can be made every 5 minutes.

How to do the calibration?

  1. Decide on the planter units or drill openers to be used for both calibration and sequential plant counts in the field. Load those with seed. (Some cardboard and duct tape work well to create a barrier or “dam” for keeping seed over only the center 5 or 6 openers of a drill.)
  2. Find a hard surface on which to “plant or drill” (drop) seed for counting. An older, worn asphalt driveway that has some deeper grooves and holes to better capture seed and minimize seed rolling tends to work well.
  3. With the soft rope, frame out a rectangle that will be used to contain seed when driving and dropping seed. Framed area should be 10 feet long X the number of rows being planted or drilled. Area that is 10 by 6 usually covers all situations. Some duct tape at the 4 corners of this frame add insurance that it won’t move when the tractor and implement are driven over it.
  4. Set the planter or drill per operator’s manual for desired drop.
  5. Count the seed dropped within the roped area. Adjust setting and redo this several times to get drop into the desired range. Once in range, do at least 2 runs to ensure consistency in drop. I expect that variation where the drop from a single run is less than 4 to 5 percent of the average will be acceptable. Convert seed drop per frame into seed drop per acre. Record values from all runs; we will use the average of the drops for a given planter/drill setting.

For another method on grain drill calibration using bags to collect seed from an operating drill go to the following Web page from Purdue University: W.pdf