How to Control the “Spill” of Your Drill

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Calibrating your grain drill doesn’t have to be complicated. NC State Extension Area Agent Tim Hambrick explains in 3 simple steps how to make sure your drill is putting out seed at the right rate in this video:

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Step 1: Population
How many seeds per acre is your target? For this example, we will use the round number of 1 million seeds per acre. When doing field calculations we need to put everything into the same type of measurement and that is typically square feet. To get seeds per acre into real working terms we have to find out how many seeds 1,000,000 is per square foot. There are 43,560 ft² in an acre. So we divide 1 million seeds by 43,560 which equals 22.9 seed per square foot.

Step 2: Drill Spacing
We need to know how many square feet each one of our seed outputs covers as we plant. If our drill spacing is 7.5 inches we need to get that into square feet. (Because 7.5″ is the width now we need to know the length of row to get it into square feet.) Since there are 144″ in a square foot, we divide 144 square inches by 7.5 inches and that tells us that every 19.2″ is a square foot of planted area. To get 19.2” into feet we divide that by 12” which equals 1.6’. That means that the drill has to travel 1.6’ of row on a 7.5” spacing in order for each seed output to cover 1 square foot of area.

Step 3:
Output How many seeds should the drill emit per seed output? The best way to determine this is to measure a specific distance and calculate how many seeds should be coming out of each output over that distance. The easiest way to do this is to get the drill wheel circumference into square footage. In this example, the drill’s drive wheel happens to be 7.9′ all the way around. (Be sure to mark a spot on the wheel so you can run exactly 1 revolution when it’s up on a jack.) 7.9′ divided by 1.6 square ft from step 2, means we are planting 4.9 square ft every revolution of the drive wheel.

To get the output: 4.9 square ft times the 22.9 seeds per square foot tells me that we’re going to be putting out 113 seeds per revolution of the drive wheel.

Remember that the number of seeds per pound in small grains can vary greatly, not just between varieties but from lot to lot and year to year. So calibrating this way can take the guess out of seeding rates and get you closer to optimizing production.

To perform your own calibration using the above method all you have to do is plug your own population, drill spacing and drive wheel information into this formula:

# Seeds      =   Population   x   Drill spacing in inches   x   Circumference of Drive Wheel in feet

————–          —————–        ———————————-         ——————————————————–

1 Output         43,560 sq ft           12 inches                                         1 Output

Ex. 113 seeds  =  1,000,000 seeds    x    7.5 inches     x     7.9 feet

—————-       ————————           —————–           ————–

1 Output            43,560 sq ft             12 inches             1 Output

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–Jenny Carleo, NC State Extension