Organic farmers wondering what crops to grow this spring are likely considering soil fertility, balanced rotations and market demands.
But ease of seed cleaning is another consideration.
Farmers commonly have plant mixtures at harvest, whether they intercrop intentionally, have volunteer plants from a previous year, or have weeds that escaped control. Usually farmers can predict what crops and weeds will dominate the coming growing season by looking at what happened last year.
It may be prudent to select a crop based on how easily the seed separates from the likely volunteers and weeds.
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When seeds are cleaned, contaminants are removed in a variety of ways. The first step is at the sieves in the combine.
Further sieving may be carried out after combining. Sieves separate seeds mostly by size, though shape can also be important.
Sieves are especially effective at removing small weed seeds from larger crop seeds, such as pigweeds from lentils. As well, some crop mixtures are easy to separate by size, such as mustard from barley or peas and barley or oats from lentils or peas.
A second cleaning stage can be done on a gravity table, which sorts seeds by weight or density. It’s the common type of on-farm seed cleaning and can be used to separate thistle heads out of peas and frosted kernels out of cereals.
A colour sorter can provide a final cleaning. The equipment is less common, so it might involve extra hauling, as well as additional time and expense.
A colour sorter may pick out pea chips from oats, for example.
Different markets have different levels of concern about contamination from unwanted seeds.
The milling oat market has a low tolerance for foreign material because their customers don’t want lentil or pea chips in their oatmeal. As well, concern over wheat allergies has led to low tolerance for wheat seeds in oats or flax in many markets.
The feed market generally has the most relaxed requirements for crop purity.
Often chips, splits and other crop types are combined in feed mixtures, and legume pieces actually add useful protein to cereal grains.
A pea-barley mixture, for instance, can be an effective intercrop for the feed market, but the two crops may not be separated well enough to sell the barley into the malting or pearling market.
This has a bearing on rotation planning. Seeding barley on pea stubble might result in pea contamination that would be difficult to remove from barley. Seeding peas on barley stubble would be less problematic.
Seed cleaners say that any crop can be cleaned out of any mixture, but it becomes a matter of economics.
Separation is usually based on the majority crop. For example, in a flax crop containing volunteer wheat, the wheat would be removed from the flax, with settings that result in a nearly pure flax sample, and a wheat sample that is much less pure. Growing flax on wheat stubble can result in difficult contamination issues, whereas growing wheat on flax stubble causes less contamination problems.
Several crop combinations present difficulties for seed cleaning. Lentil splits, especially from small lentils, are hard to remove from flax. Barley is hard to separate from either wheat or oats.
Small-seeded lentils are hard to remove from oats or wheat.
Weed removal can also be a consideration. Weeds can be difficult to remove from flax because of its small seeds. It is difficult to clean wild mustard or cow cockle from tame mustard.
Wild oats are tougher to separate from an oat crop than from other cereals.
Seed cleaning options are critical in planning a successful intercrop.
They can also be important in rotation planning, as this year’s crop is likely to be mingled with volunteers from last year’s crop.
Knowing which seeds can be separated easily, and which separations require more time, effort and expense, can make planning more effective.
Tracy Salisbury, B.S.A., is an assistant in Organic Research and Extension at the University of Saskatchewan.
Brenda Frick, Ph.D., P.Ag. is the Coordinator of Organic Research and Extension at the University of Saskatchewan and an OACC Affiliate. She welcomes your comments at 306-966-4975 or via email at organic@usask.ca.
