This season’s oilseed rape faces tough challenges

A slow start to the cereal harvest and one of the wettest summers on record could make establishing oilseed rape this season particularly challenging for many growers.

“If soils stay as waterlogged as many currently are, we could see the same sort of harvesting difficulties and delays we had in 2007,” says David Langton, technical manager for Agrii.

Compaction, sodden soils and a late harvest will all put pressure on next year’s oilseed rape crop, and getting the establishment right, especially when pushed for time, will be essential this year.

“The first 30 days’ growth can have a massive effect on yield potential,” says Mr Langton. “Depending on conditions, the difference between well-established and badly established crops can be as much as 0.5t/ha.”

Establishment

Single-pass sowing using a sub-soiler or cultivator seeder could prove to be the best establishment option in this season’s extraordinary conditions with seed-bed conditions far from ideal.

“The key benefit of the single-pass system is that it makes the most of the short window after the combine,” says Mr Langton. “With limited time, fewer passes will be advantageous, depending on conditions.”

Deciding how deep to drill and how wide the spacings are is dependant on the soil conditions and variety choice.

For more on this: See all of the articles on High 5 OSR yields

“It may pay off to work the tines a little deeper this year as they will be able to tackle the inevitable soil compaction that could be caused at harvest,” says Mr Langton.

As well as getting depth right, spacing is also important. Row spacings of 45-55cm will take maximum advantage of the tine’s cultivation ability,” says Mr Langton.

Nutrition

Rapeseed contains little of its own nutritional support, so in the early growth stages the new roots require immediate access to the right nutrients in the soil.

“This will be particularly critical for rape crops drilled later in the season, as they can struggle to scavenge the right nutrients in the short window before temperatures drop this autumn,” says Mr Langton.

Added to this, cold, wet soils in September could see poor nitrogen mineralisation, making seed-bed nitrogen important. One option for growers using a single-pass system is band applying nitrogen directly on to the area being drilled with mounted nozzles.

“The maximum rate that can be used in Nitrogen Vulnerable Zones is 30kg/ha for seed-bed nitrogen. The advantage of applying it directly to the seed-bed is that you know it’s going to be easily available and, therefore, be taken up by the new roots,” says Mr Langton.

“In this year’s trials near Swindon we were able to achieve a green area index increase of 0.5 with this approach,” he says. Achieving an increase in cover will mean you have a more robust and stronger-rooting crop going into the winter.

Ensuring phosphate levels are adequate will also be essential this autumn, particularly with the plant’s limited rooting ability. “Growers could look at the potential to apply phosphate with nitrogen when drilling, says Mr Langton.”

The specialist seed treatment Take Off could be another option this autumn. Equally, phosphite in any early winter spray will be invaluable in further promoting rooting, which could easily be compromised by the cold, wet conditions.

Rates

“In our trials we have been looking at seed rates, drilling plots from just two seeds/m of row right up to 42/m length. The difference, as you would expect, is marked.”

Lower plant population than generally recommended gives the best canopies. Most growers tend to get crops too dense for optimum light interception and yield because they sow them too thick. And it adds extra seed costs and can increase the chance of lodging.

Avoiding too dense a canopy could be an important message for growers considering upping seed rates to offset the predicted high slug pressure or poor establishment conditions this year.

Based on the trials, he advises aiming for a plant population for hybrid varieties of 20-25 plants/sq m and a higher population of 25-30 plants/sq m for conventional types.

“Plant establishment can be as low as 50% in challenging ground conditions and in the later window,” adds Mr Langton.

Therefore, he believes drilling at 40-50 seeds/sq m should be adequate for hybrids, maybe 50-60 seeds/sq m with conventional varieties, and this will allow for the potential 50% failure rate and yet still achieve optimum plant populations.

“Although it depends a lot on the field conditions,” says Mr Langton.

“Slug pressure this year is going to be very high, and oilseed rape can be very susceptible to slug damage,” adds Mr Langton. “Growers should be applying slug pellets at the time of drilling, and monitoring conditions closely.”

Wiltshire: David Sanderson 

David Sanderson grows 1,000ha of combinable crops – including 265ha of mainly DK Cabernet oilseed rape – in the South West near Swindon on a range of chalks and some deep clay.

“Harvest this year is looking challenging, especially on our heavy clays, which are completely waterlogged,” he says. “The chalks aren’t so bad, as they drain well but we are desperate for a long spell of sunshine.”

He expects his investment in a one-pass establishment system for oilseed rape three years ago will pay off particularly well this year.

“We made the decision to adapt our Spaldings Flatlift subsoiler by adding a seed box and since then we have seen yields increase by up to 20% to average 4.95 t/ha due to the better establishment.”

Mr Sanderson continues to drill conventionally on the lighter land, making the most of his Flatlift’s flexibility on the heavier land. He emphasises the need to roll as soon as possible after drilling in what could be a bad slug year.

In response to current conditions, he and his Agrii agronomist, Tim Horton, plan to increase their reliance on hybrids such as Excalibur which stand out for their fast leaf development challenge, and establish more of the crop with the one-pass subsoil seed box unit, even on the chalk soils.

Unless the weather markedly improves, they expect their risk assessments will necessitate applying slug pellets to the heavier fields at drilling this autumn.

“Early weed control will depend upon how well seed depth can be controlled at drilling,” adds Mr Horton. “We shall be treating pre-emergence, if possible, but may have to fall back to post-emergence Katamaran Turbo (dimethenamid + metazachlor + quinmerac) at full cotyledon in some cases.”

High 5 Challenge

Farmers Weekly has teamed up with Dekalb to help growers increase average rapeseed yields to 5t/ha or more. Watch our series of four videos in which Agrii agronomist David Langton looks at establishment and how to get a 5t/ha crop off to a flying start.