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Combine Harvest Loss from a Kernel Count

Also known as combine loss · harvest loss · shatter loss · kernels per square foot loss · grain loss check

L=n w10001000L = \frac{n \, w_{1000}}{1000}

Enter your known values, leave one input blank, and solves for the missing one. Try different units for next level excitement!

See also
Small Grain Yield Estimate — Uses the same thousand-kernel weight, from the other end of the season.Crop Yield per Unit Area — Loss is only meaningful next to the yield it is being lost from.Bushels to Mass by Test Weight — Loss is argued in bushels per acre, and this is the bridge to it.

Learning zone

The cheapest yield increase available to most farms is not a fertiliser or a variety, it is a hoop and five minutes. Grain left on the ground behind a combine is grain already grown and already paid for, and the check that measures it is a kernel count: throw a frame of known area on the ground behind the machine, count the loose kernels inside it, and multiply by the weight of one kernel.

The arithmetic is one line, and it explains the rules of thumb every operator half-remembers. Two corn kernels per square foot, at a 300 g thousand-kernel weight, is 2×43,560×0.3=26,1362 \times 43{,}560 \times 0.3 = 26{,}136 g per acre — 57.6 lb/ac, which is 1.03 bushels. That is where "two kernels to the bushel" comes from. For wheat the same arithmetic gives about twenty kernels per square foot to the bushel, because a wheat kernel is a tenth the weight of a corn kernel. The rules of thumb are not lore; they are this equation with the crop's kernel weight substituted in.

Where the count is taken decides what it means, and this is the part most often done wrong. Kernels found AHEAD of the machine were shed before it arrived — pre-harvest loss from lodging, shattering or bird and hail damage — and no amount of adjustment recovers them. Kernels found behind the header but ahead of the separator point to header loss, which is usually reel speed, cutter bar height or gathering chain condition. Kernels in the chaff stream are separator or shoe loss, which is fan speed, sieve settings and rotor clearance. Subtracting the pre-harvest count from the behind-the-machine count is the only way to know what the combine is actually responsible for.

Two corrections stop a good count from lying. The straw and chaff leave through a spreader narrower than the header, so a count taken under the discharge must be scaled by the ratio of header width to spread width — commonly a factor of two or more, and forgetting it makes the loss look far worse than it is. And there is an economic floor: chasing the last fraction of a percent by slowing down costs more in harvest capacity and weather risk than the grain is worth. One to two percent is normal, three is worth investigating, and above five something is genuinely wrong with the setup.

Combine Harvest Loss from a Kernel Count
L=n w10001000L = \frac{n \, w_{1000}}{1000}
nw1000L
Where
  • LL= Yield lost per unit area (kg/ha)
  • nn= Kernels per unit area (per m²)
  • w1000w_{1000}= Thousand-kernel weight (g)
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