While varietal traits such as vigour, yield and disease resistance are rightly high on the agenda when assessing varieties, oil content is often overlooked. But even a small percentage difference can make a noticeable difference to the crop’s gross margin once bonuses are included, says the firm’s seeds manager Colin Button.

“Oil content is predominantly determined by the crop’s genetics, so even in a season when seed yield is down it is still possible to get a high oil content, which can give a useful boost to the overall value of the crop.”

Average oil contents of recommended varieties have increased by some 2.5% from 43.3% to 45.8% over the past decade, which at an ex-farm osr value of £270/t [as seen last harvest] roughly equates to an extra £50/ha on a crop yielding 5t/ha, Mr Button explains.

“If your crop produces closer to 4t/ha rather than 5t/ha for whatever reason, you’re still better off going for maximum oil yield.”

That trend of rising oil contents in Recommended List trials has been reflected in results from commercial crops delivered to store over recent years, says Gleadell’s seed manager Chris Guest.

“Oil content does still fluctuate from season to season, but it is generally more stable than some of the yield figures which can vary quite widely year to year.”

Mr Guest agrees that more attention should be given to oil content when making variety decisions, especially as there is still quite a range of oil content across varieties on the current 2014/15 HGCA Recommended List. The best, Compass and PR46W21, are up at 46%, while the lowest comes in at 43.9%.

“When you look at where we’ve come from 10 years ago when Winner had the highest oil content at 43.3%, we’ve come a long way. We’re now seeing content in the high 46s and above 47%,” he says.

Indeed, Mr Button says there have been situations in the past where oil content of above 48% have been reported in the trade and in those cases growers will be getting quite a bonus back. “It’s by no means widespread, but shows it is possible from the varieties currently available.”

Rising trend continues

New candidate varieties look set to continue the trend of rising oil content for now at least. The best in terms of oil content is the conventional variety Advance at 46.7%, but many are close to, or beyond 46%.

At a rape price for harvest 2014 of £270/t ex-farm, producing a crop with an oil content of 46.7% would be worth £27.14/t in total oil premium. On a 4.5t/ha crop, that would add approximately £50/ha to the crop’s gross margin over a lower oil content (44%) variety, Mr Guest says.

“New varieties such as Advance really do look to have the potential to push oil content even higher.”

But Mr Button notes that the theoretical maximum oil content is around 50%, as beyond that you start to see a reduction in seed coat strength that causes problems for crushers and storage due to leakage from the seed coat. “The best performing varieties aren’t far off that maximum level now, but there is still scope for average farm performance to improve.”

There is no correlation between hybrid or conventional varieties and high oil content, he notes. The two highest that are currently recommended are both hybrids, but the candidate variety with the highest oil content is conventional. “It’s not surprising given that hybrids are created from the best traits in conventional varieties anyway. Oil content is one of those traits.”

Weather still key

Mr Button acknowledges that while genetic capacity is the baseline factor influencing oil content, the weather during the key period for building oil content (seed set to crop senescence) can still have a big impact.

“Crops need good sunlight capture during that period and it is vital nothing within the grower’s control is allowed to impinge on that. This means plant health must be maintained by keeping crops free from late-season pests and disease as long as possible. Don’t underestimate the contribution that the pod itself delivers to seed yield and oil content.”