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Soil Health Resource GuidePlanting


By January 15, 2018December 10th, 2019No Comments

So, you have gotten the perfect mixture to fulfill your needs, getting the seed loaded in the drill then, thought hits you that drill has no cover crop setting. Hopefully this information helps mitigate the scenario of running out of seed with 10% of your acres to go. Nobody wants to make that call to buy more seed that you already had shipped for those acres.

Before we can move forward you must understand bushel weight and how they vary between species. Bushel weight is a historic standard unit of pounds per volumetric space. It signifies the amount of weight it takes a product to fill 32-quart containers or 1.2445 FT3 make up a bushel. This method of selling grain was an easy way to sell commodities without the need for weight measurement devises. Then it was noticed that not all products are equally dense. So, the system was fine tuned to accommodate for test weight. So denser products were rewarded with a better price and lighter products would get penalized.

Here are the official bushel weights for common us grain crops as follows…

U.S. Commercial Grain Bushel Sizes


Weight per bushel



Weight per bushel

Alfalfa 60 lb Grass, Orchard 14 lb
Barley 48 lb Grass, Redtop 14 lb
Clover, Alsike 60 lb Grass, Timothy 45 lb
Clover, Crimson 60 lb Lespedeza 40-50 lb
Clover, Ladino 60 lb Millet 50 lb
Clover, White 60 lb Oats 32 lb
Clover, Red 60 lb Rape 60 lb
Clover Sweet 60 lb Rye 56 lb
Corn, shelled 56 lb Sorghum, forage 50 lb
Corn, ear 70 lb Sorghum, grain 56 lb
Cotton 32 lb Soybeans 60 lb
Cowpeas 60 lb Sudan grass 28 lb
Flax 60 lb   Sunflower (oil type) 24-32 lb
Grass, Brome (smooth) 14 lb   Trefoil, Birdsfoot 60 lb
Grass, Blue 14 lb   Vetch 60 lb

Data from the University of Missouri’s Agricultural Publication G4020, by William J. Murphy, Department of Agronomy.

Some will use this information to determine their drill setting. Simple take the products in your mixture determine their bushel weight. Use this information to then calculate what the overall average bushel weight of the mixture would be. Some trends you will find…

  1. If your cool season mixture is diverse in that it has oats or barley and a balance of other products you will use the barley setting.
  2. If your warm season mixture covers everything from millets to sunflower to corn, you will use the milo setting.
  3. If your using a mixture of seed that is dominated by one product then just use that seed for the setting. A good example is if your planting a winter cereal with clover and radish. The clover and radish are such a minor percentage of they overall weight that they don’t make a difference on the setting.

We will now look at each method in a little more detail and try to provide some additional helpful links.

Method 1- Calibration Tool

The simplicity and relative accuracy of this tool makes it by far my favorite for the job. These can be purchased from Green Cover for $60, just ask your sales rep. If you have any intention of continuing to plant diverse mixtures, it won’t take to many acres of running short on seed to cover this expenditure.

Quick tip: If you have a larger driller that has two separate metering adjustments then you can test both sides on different settings to see which one is closer to the desired output. Or make an averaged assumption between the two results so you only calibrate once.

The steps to utilize this tool are on a sticker attached to the side of the cup. These steps are as follows, with some added tips…

  1. Attach collection bag to one of the seeder outlets.
    • We suggest taking samples from numerous drop cups. As drills can vary greatly between drops based on wear. To collect extra samples, use plastic sandwich bags and rubber bands.
  2. Choose your row spacing and travel distance from the chart.
    • If you don’t already know your row spacing, use a measuring tape to determine distance between disk openers. If your units are staggered, then measure distance between two back units and divide that number by 2.
    • The chart they refer to is on your cup sticker. Look for the distance associated with your row spacing.
  3. Carefully measure and mark the number of feet to travel.
    • We recommend placing some very visible flags or markings for the tractor operator. Spray paint works good.
  4. With drill engaged, drive the travel distance catching sample.
    • At this point the instructions assume that your drill is full of seed, but you have some choices here. You can fill your drill with seed and be planting as you calibrate OR just put a couple handfuls over the drops that you will be collecting. This way if your calibration doesn’t go to plan you can still drill that same test strip without doubling up on the seed used.
    • Note that when you first fill your drill, the cups you’re collecting need to be primed so when the clutch releases your seed immediately starts falling. Prime your drill by planting 100 ft before you start calibrating or simply take your fingers and push the seed down into the meters.
  5. Remove bag and pour sample into seeder meter canister
  6. Seed sample must be level in canister before testing.
    • It’s critical that you have the seed level as possible for an accurate measurement.
  7. Support scale by ring and slide weight on beam until level.
  8. Read pounds per acre above center of weight cube.

Method 2- Weigh Out

This method is a little more primitive as you would be reacting to a known amount of weight being distributed over a known amount of area. If you get your seed in 50# bags, then this step is easy to know the weight of the seed going in. If you’re getting your seed in totes or bulk and want to utilize this method, then just ask your rep to bag up 150-200# of your blend for this purpose. We suggest running the drill over at least 3 acres or more that would end with an even increment of 50# of seed that should have been planted. This would require you to have a known acreage amount of a small field or an acre meter on the drill.

Method 3- Manual Calibration

Doesn’t get any more accurate than this method here but it requires a few more tools and some math skills. No one describes it better than Jim Johnson with the Noble Foundation so I’ll leave that up to him in the video above. Tools that will be needed are:

  • a wheel jack
  • flexible tape measure
  • roll of adhesive tape
  • five light weight cups or plastic bags (ex Styrofoam coffee cup or sandwich bags)
  • gram scale
  • calculator
  • possibly a helping hand (you can do this yourself if you tape the cups or plastic bags to the drops).

Method 4- Air Seeder Calibration

Not much else needs to be said here. You already have a built-in calibration tool that was worth the money.

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