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Updated: August 8, 2017
The seeding chart on your grain drill is a good start to determine seeding rate but may be significantly off target due to variations in seed size within species as well as wear and tear of the drill. So it makes sense to check seeding rate. You can unhook some seedtubes and tie a small bag or cup to them and run a certain distance with the drill. The chart below helps you to calibrate the drill. The measures make sure that you collect seed for 100th of an acre so that you can just multiply the weight of the collected seed by 100 to get the seeding rate in lbs/A. By using 100th of an acre you avoid large errors to due starting and stopping the drill.
Another way is to weigh out seed for, say, two to five acres (depending on desired seeding rate) and put it in the drill. Then you drill an acre or four (less than what you put in the drill to avoid running low on seed in part of the drill). You use the acre meter on your drill to know how many acres you planted. You can then vacuum out the seed that is left with a shop vac and weigh how much seed was left in the drill. The seed you drilled is the difference between the weight of the seed you put in the drill and the seed that is left over. Divide this by the area drilled to get the seeding rate.
A more detailed guide to seed drill calibration can be found in the fact sheet: "Calibration of Grain/Seed Drills", which is available from your local Extension office.
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