Growing need for oilseeds

Supply is down and demand is growing, so there are lots of opportunity with this proven crop. Ciarán Collins, Teagasc tillage specialist and John Pettit, Teagasc tillage advisor, Wexford discuss the Growing need for oilseeds.

Pictured above: Don Somers

The area of winter oilseed rape is expected to increase this autumn, primarily due to the substantial rise in the price of oilseeds. Other attractions are the potential nitrogen savings when good growth and development is achieved in the autumn/winter period, grass and other weed control options and significant yield increases in following crops.

The five year average area of winter oilseed rape (2017-2021) is 8,900ha, but estimates from DAFM indicate that the area increased significantly for the 2022 harvest to 14,500ha. The average yield of winter oilseed rape has remained consistent over the last five years at 4.4t/ha, with some growers regularly achieving 5t/ha.

Improved varietal traits, such as for pod-shatter resistance, phoma and light leaf spot resistance and turnip virus yellows resistance, have contributed to the consistency of today’s winter oilseed rape crops.

Winter oilseed rape and nitrogen

Winter oilseed rape has a high nitrogen requirement (225kg/ha at index 1) but significant savings can be achieved through good canopy development in the autumn/winter period. Target Green Area Index (GAI) at flowering is 3.5, but savings on nitrogen (€750/t) of €277/ha are possible in a crop with a GAI of 2.0 compared to a small crop with a GAI of 0.5. Brassicas are very efficient users of nitrogen and growers are increasingly incorporating organic manures to help crop growth in the autumn.

Sowing oilseed rape at the optimum timing of mid- to late- august can be challenging during a busy harvest, but research carried out at Teagasc Oak Park shows oilseed rape can be successfully established using time saving min-till or strip tillage. Yields from these systems are comparable to plough-based systems.

Pests

Regardless of the establishment system, timely sowing is crucial for canopy development and to realise the benefits of lower nitrogen application and reduce pigeon grazing. Slugs and cabbage stem flea beetles are the most common pests in the autumn.

The area of oilseed rape in the UK has reduced dramatically in recent seasons, due to insecticide resistance and an inability to control cabbage stem flea beetle. While this has not been an issue in Ireland to-date, only using insecticides when thresholds are exceeded is vitally important. Pigeons are a serious pest in the spring, but damage is less likely in large canopies.

Winter oilseed rape can be highly profitable in its own right, but profitability should be viewed across the entire rotation. Yield increases in winter wheat after breaks for disease of up to 19% have been recorded in Teagasc experiments when compared to continuous wheat.

Don Somers, Teagasc Signpost farmer

Don Somers, a Teagasc Signpost farmer based in Co Wexford, has grown oilseed rape for the last 17 years. Recent years have seen Don achieve more desirable yields, making the crop a much more attractive option to grow. A contributing factor to more consistent yields is drilling crops earlier and applying organic manures to produce crops that have a larger GAI in the spring. Having a larger GAI in the spring makes it much easier to achieve the target GAI of 3.5 at flowering, particularly in years when pigeons are active or if there is poor growth in February and March. Crops with a more significant GAI in the spring also offer a number of other benefits. Such crops have the potential to capture more soil residual nitrogen during the autumn/winter period, reducing the threat to surface and ground water. This also makes a contribution to profitability, since less nitrogen needs to be applied to the crop in the spring, thus reducing the cost of production. Don also applies the final split of nitrogen in liquid form – this enables nitrogen to be applied to the crop later.

Oilseed rape offers the farm a range of benefits

It enables the control of problematic grass weeds with alternative chemistry, preventing such weeds from becoming an issue on the farm.

Oilseed rape also helps to broaden both the drilling and harvesting periods, using labour resources on the farm more efficiently.

The crop also helps to make a significant contribution to soil health. Its deep taproot helps to improve soil structure and the incorporation of straw returns a significant quantity of carbon to the soil.

The challenges

Don recognises that oilseed rape can present a number of challenges, however. Drilling it early can be challenging, since it can coincide with harvesting alternative crops.

Previous crops need to be harvested relatively early to enable the oilseed rape to be drilled, hence a bit of forward planning is required. When using cover crops within the rotation, there is a need to be selective with species to avoid building club root levels in soils and avoid particular cover crop species becoming problematic weeds within crops of oilseed rape.

Harvesting oilseed rape can be very challenging with unfavourable weather conditions and there may be a need to compromise on the crops moisture to ensure that the crop is harvested prior to the crop shedding seed. The oilseed rape crop also requires an investment in machinery, in the form of a side knife and preferably an extendable table for the combine head.

This article was first published in Today's Farm - July/August 2022 where you can read more articles like this one. 

Find out more information and advice from the Teagasc Crops team here.   The Teagasc Crops Specialists issue an article on a topic of interest to tillage farmers every Thursday on Teagasc Daily.  Find your local Teagasc office here