It may be all too tempting to use the seed chart that was provided with your grain drill as a basis for setting a seeding rate. Like looking at a nozzle catalog for applying fertilizers or chemicals, this will get you “close” to where you need to be.
The only way to ensure you know your seeding rate is to calibrate your planter or drill. There can be many different variables that affect seeding rate including: differences in seed size, seed coatings, and seed treatments.
The process to calibrate your drill can be done as follows:
1. Determine your distance for calibration. In our example, we will travel 200 feet. Make sure this distance is practical and captures field variability. Multiply that distance by the working width of the drill. If you have a 15 foot drill, that would be 3,000 square feet. Next, divide that 3,000 by 43,560 and you will get 0.069 acres covered in the 200 foot pass.
2. Next, mark off your 200 foot course using a tape or measuring wheel. Also, examine which wheel actually drives the seed metering device. This could be one of the ground-driven wheels, or another wheel that only runs the metering. You will need to determine the number of revolutions this wheel turns in 200 feet. Marking or wrapping the wheel with duct tape will help you count more easily. Travel this distance and count revolutions at least twice, and use the average.
3. Park the drill, and use a hydraulic jack to lift the drive wheel so it spins freely. You may have to lower the hydraulics on the drill to engage the drive. Disconnect the bottom of three (3) seed tubes and place each seed tube into a small measuring container.
Fill each of the metering cups with seed, ensuring there is enough seed for the calibration process. Using duct tape across unused cups can save you time when cleaning out the drill. Rotate the drive wheel several times until seed falls from each tube. Be sure to empty your containers before going to the next step.
4. Rotate the drive wheel the number of times recorded in step #2 above. Take the three containers and weigh the contents individually (a scale that weighs in ounces is most commonly used). Be sure to obtain only the weight of the seeds, subtracting the weight of the empty container (using tare weight only).
Calculate the average weight. Then multiply by the number of openers on the drill. For example, if our weights were 3.1 oz, 3.0 oz, and 3.1 oz, our average was 3.06 oz. If we had 23 openers on our drill, the total amount collected would be 70.38 oz, or 4.4 lbs.
5. Finally, take your weight of seed collected and divide by the acreage calculated in step #1. Then multiply by seeds per pound (listed on the seed tag). In our example, 4.4 lbs / 0.069 acres = 63.77 lbs. of seed used in 1 acre. If our seeds per pound is 2,500, that would equate to a seeding rate of 159,420 seeds per acre.
Maybe that’s what you were shooting for…or maybe not! Hopefully, you’re in the ballpark, and with a minor adjustment, you can achieve the seeding rate you desired.
For more information on calibrating your drill, you can refer to our Penn State Agronomy Fact Sheet.