Average on-farm oilseed rape yields are around 2.5t/ha below crops in trials, but this gap could be cut significantly by better targeting of varieties and inputs to specific field conditions.

That’s one of the main messages from CPB Twyford, which is running a series of open days across the country, looking at how growers can maximise the potential of oilseed rape crops.

In particular, the trials highlight several key factors.

Variety profile and site potential

One of the most important starting points is the development profiles of different varieties and whether they are suited to early, mid-season or late sowing, says the CPB’s Julie Goult.

“For an early sowing variety you need short, stiff straw so that it stands well, develops slower over winter and has good disease resistance, due to the prolonged exposure.

“For mid-season sowing, most types will cope, whereas for late sowing, you need vigorous autumn growth, plus early flowering and maturity.”

In recent years new hybrid varieties, such as the firm’s Trabant, have narrowed the yield gap to conventional types and in future, they could have a yield advantage, she predicts.

Low biomass semi-dwarf varieties may be ideally suited to early sowing situations, adds colleague Lee Bennett.

He urges growers to pick varieties according to the yield potential of the site.

“For example weaker straw varieties, such as Winner are more suited to low potential sites, whereas those with stiffer straw may be better on more productive sites.”

Establishment

Establishment method has a major impact on rooting structure and in some cases autocasting rape can significantly stunt root growth, Mr Bennett says.

Varieties differ in their suitability to different techniques, with most suited to plough-based systems and till seeding (eg with subsoiler) although hybrids are more suited to minimal “scratch and sow” systems, he says.

“Root system is the number one factor for high yield,” stresses Andreas Baer, from German sister company NPZ Lembke.

“Strong root structures are better able to utilise nutrients and the thicker stems contain more lignin, which provides extra protection against diseases such as phoma.”

A deep tap root can also improve soil structure and root penetration of the following crop, he notes.

Sowing date and seed rate

Growers should always sow oilseed rape based on plants per square metre, continues Mr Bennett.

“If you’re still sowing at pounds per acre, it’s wrong – there will be a massive difference in what’s actually going in the ground.

Always sow by plant numbers and thousand grain weight.”

He believes there is real scope to cut seed rates.

“Standard practice for many growers is to sow 50 seeds/sq m, but reducing rates to 25 seeds/sq m would halve seed costs with no detrimental effect on yield due to the increased branching.”

Management regime

Autumn triazoles can play a key role in management programmes, particularly where canopy manipulation is required.

The approach is more widely used in Germany, where products such as Caramba (metconazole) can also reduce the incidence of stem canker by reducing the available stem area for infection, says Mr Baer.

Nitrogen is another key area. The taller the plant is coming out of winter, the more chance there is of being able to reduce the amount of nitrogen applied, he says.

“In some cases it may be possible to reduce applied fertiliser to 30-40kg N/ha, but weaker root systems will need more.”

paul.spackman@rbi.co.uk