Mixed Crops in Harvested Grain: When Size Screening Is Worth Trying

A size difference can give you a way to separate the crops

When another crop is mixed with your harvested grain, a substantial difference in seed size makes screening worth trying. A screen can let smaller seed pass through while holding larger seed back, helping recover separate crops. Judge the result by checking both outputs against the original mixture—not just by how clean the retained grain looks.

Look for a useful gap in seed size

The useful difference is physical: screen openings must let one crop pass while keeping the other back. If the crop you want to retain is larger, screening can remove smaller seed from it. If your desired crop is smaller, the useful grain may be the material that passes through.

NDSU’s Northern Great Plains intercropping guide identifies a substantial seed-size difference as an aid to post-harvest separation.

Overlapping sizes limit that separation. Some seed from the other crop can travel with the grain you want to keep because it fits the same openings. Penn State’s oilseed-cleaning guidance explains this screening limit: correctly sized screens remove larger and smaller seed, but seed close to the desired seed’s size can remain.

For example, field pea and canola have substantially different seed sizes, making them candidates for size-based separation after intercropping. The larger peas and smaller canola seeds may be collected as separate crop outputs when the screen setup works as intended. Chickpea and flax offer another example of crops with a useful size difference. These examples illustrate the principle; actual separation quality still needs to be checked with the harvested mixture.

Compare the original mixture and both outputs

During a trial, keep a representative sample of the original mixture and collect separate samples from both outputs after the cleaner reaches steady operation. Spread each sample out and compare the crops present. For a more useful comparison, take equal-weight samples from each output and sort the desired crop from the other crop by hand. Weigh the portions to estimate the percentage of each crop in that output. Also record the total weight collected from each output so you can see how much of each crop is being recovered, not just how clean a small sample looks.

Give each comparison a clear purpose:
– Original mixture: identify the crop you want to keep and the other crop you want to separate.
– Retained grain: look for seed from the other crop that remains mixed in.
– Removed material: look for desired grain leaving with the separated seed.

A cleaner-looking retained sample does not tell you how much useful grain went out the other way. Desired grain in the removed material shows a recovery problem; the other crop still in the retained grain shows incomplete separation. Check samples during the run rather than relying on one early look. Regular sampling during cleaning is also part of NDSU’s foundation-seed guidance.

Do not automatically call the smaller-seed output waste. It may contain a second crop worth recovering separately. NDSU’s intercropping guide illustrates this distinction with separate crop outputs and a separate collection for screenings—the material removed during cleaning. Keep those purposes distinct when judging your own trial.

Where VDSC and Metra setup help fit

Metra’s VDSC grain cleaner screens by size and can separate different crops when their seed sizes differ. A standalone VDSC may be sufficient when size screening does the job; mixed grain does not automatically require a larger cleaning setup.

Metra helps choose equipment and settings for your material. The useful goal is to separate the unwanted crop while keeping the grain you intend to recover, with both outputs considered in the setup decision. If the two crops have substantially overlapping seed sizes, screen adjustments alone may not produce a satisfactory split. A sample test helps determine whether size screening is sufficient or whether another separation method should be considered.

Contact Metra at +1 701 515-0488 or [info@graincleaner.com](mailto:info@graincleaner.com) to arrange a free grain sample test. The manager will help agree the sample quantity and shipping or demonstration arrangements.