Size matters for OSR establishment

Farm-saving seed is a valuable way of minimising seed costs, but it doesn’t necessarily mean scrimping on quality. Tom Allen-Stevens reports

Many factors contribute to the quality of farm-saved seed, but size is one of the most important when it comes to getting an oilseed rape crop off to a good start.

Work carried out by the National Association of Agricultural Contractors (NAAC) suggests bigger seed grows with far more vigour than smaller seed.

“It’s always been our belief that it’s more about seed size,” says Nigel Day from mobile seed treatment specialist Anglia Grain Services.

NAAC set about proving this by growing seeds of different sizes on paper and sand and measuring the seedlings after seven days. The seeds came from the same sample, but were sorted by diameter. At seven days the seedlings from the larger seeds had produced two-and-a-half times more dry matter, had visibly thicker stems and wider cotyledons (see table).

The results should encourage farmers to farm-save oilseed rape and ensure the mobile seed processor sieves out the boldest seed from the sample, says Mr Day.

When farm-saving, growers can boost seed size in cereals through the use of an ear spray. With oilseed rape, drilling on the thin side (less than 40 seeds/sq m) will encourage production of larger seed, says Mr Day.


Weeds and disease control is also critical for seed quality and Mr Day recommends growers earmark a fertile, well-drained and clean area. “Use the rotation to achieve a volunteer and disease-free crop.”

The most important weeds to avoid with oilseed rape are charlock, wild radish, and cleavers. For cereals, the key ones are wild oats and sterile brome. To ensure the crop is weed-free growers should rogue if necessary, he adds.

At harvest, growers should allow crops to ripen naturally or desiccate using diquat if needed, Mr Day says. “Avoid using glyphosate as this can affect germination.”


Oilseed rape should ideally have a moisture content of 9% and be kept in half or one-tonne bags. With cereals, the ideal moisture is 15% and a trailer or bin is the best storage vessel. If grain needs to be dried following at harvest, a high volume, low temperature (less than 30C) system avoids the risk of seed damage.

Cleaning and treatment

If you keep seed over until the following year a germination test should be carried out before planting. Normally, it would be 95-99%, says Mr Day.

“Make sure the cleaning and treatment contractor is on the Verified Seed Scheme and get seed passed over a gravity separator and sieved well to get the best sample settings.”

This year, variable crops mean growers might have to remove as much as half the seed crop in screenings. This should be considered when assessing how much of a crop should be set aside for seed.

Finally, Mr Day recommends using an effective seed treatment. “At the very least protect against bunt, smut and damping off.”

Certified vs Farm-saved




Guaranteed purity


Grown on land with no rape crop for 10 years

More control over how seed is grown


More screenings can be removed

Tested by independent lab

Rapid turnaround possible

You can grow a new variety

You can closely evaluate the performance of a variety

Only way to grow a hybrid

Flexibility of seed treatment


Seed diameter



Thousand grain weight



Dry matter at 7 days*



*Initial weight of seed discounted


New rules on glucosinolate levels

Oilseed rape growers should be wary of restrictions on glucosinolate levels that may affect autumn 2011 plantings.

The Federation of European Oil and Protein Processors (FEDIOL) has placed limits on the amount of glucosinolate in oilseed rape cake. After harvest 2013, crushers will only accept varieties containing less than 18 µmol (micromoles) of glucosinolate.

That means growers establishing crops destined for farm-saved seed this autumn must use certified seed of a variety tested below 18 µmol at the time of registration. Farmers should retain the certification label of this seed as well as the invoice, which gives the time of delivery and volume received.

The new rules will affect very few varieties and should not be misinterpreted as a restriction on all farm-saved seed, says NAAC.

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