Matt Morris, Agriculture Agent
University of Maryland Extension, Frederick County
Grain drills are important pieces of equipment on the farm. Many of them were put to work reseeding pastures and hay fields that needed a makeover after our record rainfall last summer and winter, while others will head to the field shortly to plant late season soybeans or summer annual forage crops. With that in mind, I always urge everyone to calibrate their grain drill each time seed type or size is changed. Remember, the seed chart on your drill is a starting point and is based on brand new tires and some baseline seed types and sizes. More often than not it is discovered through calibration that the seeding chart on the drill was several pounds per acre off. There are multiple ways to do this and I personally will use different methods depending on the situation. Below I will outline, step by step, one way to calibrate your 7.5 inch row-spacing grain drill. This process can be done with any seed type, not just forage seed.
There are a few tools you need in order to do this process successfully: a gram scale that measures to at least the tenth of a gram, sandwich bags and rubber bands to collect seed, flags to mark 100 feet (if pulling the drill), and a small cup to weigh the seed in.
Step 1) Use the drill’s seeding rate chart to get an initial drill setting for the process.
Step 2) Place a small amount seed above a few seed cups in the seed box.
Step 3) Lower the drill to engage the drive mechanism and drive a few feet to make sure the seed cups are full of seed.
Step 4) Remove the seed boot and rubber band a sandwich bag to the bottom of the seed cups you put your seed in during step 2.
Step 5) Pull the drill 100’. You can also determine the amount of wheel rotations in 100’ and spin the wheel by hand instead of pulling the drill. The formula to determine the revolutions in 100’ is: 100/ (3.14 X diameter of the drive wheel in feet) = Number of revolutions.
Example: 100 ÷ (3.14 X 3.5’ diameter) = 9.09 revolutions of the drive wheel to equal 100’.
Step 6) After pulling the drill or turning the wheel by hand, remove the seed collection container.
Step 7) Make sure your gram scale is zeroed out with the cup you will weigh the seed in on the scale.
Step 8) Weigh the seed you collected from each row, individually, in grams.
Step 9) Average the weight of seed collected from each row.
Step 10) Pick your desired seeding rate in pounds per acre. For this example we’ll use 20 pounds of orchardgrass per acre.
Step 11) Use this formula to determine the drill’s seeding rate per acre based on what you collected in 100’: weight of seed collected (g) X 69,696 ÷ 454 ÷ 100 = Lbs/acre output from the drill
Example: You collected an average of 13.03 grams of seed from each row. 13.03g X 69,696 ÷ 454 ÷ 100 = 20lbs of orchardgrass/acre.
Step 12) Adjust the seeding rate up or down based on the amount of seed collected until you hit your target seeding rate per acre.
If you have any questions on this process or have a drill with row spacing other than 7.5 inches, do not hesitate to call or email me with questions. I am also happy to come out and help you calibrate your drill whenever you’re ready to plant.
