Managing later drilled OSR crops

Hot dry summers, milder autumns and a deeper understanding of cabbage stem flea beetle behaviour have seen the drilling of winter oilseed rape delayed in recent seasons. As the window has moved, the questions around timing, plant vigour, variety selection and crop management have become more, not less, important.

The window has moved

Craig Padley, who runs NPZ UK's trial sites in Cambridge and Wisbech, says the old drilling calendar no longer holds.

"It used to be that we'd drill by the 10th September, but with climate change that's no longer relevant," he says. "I would be happy to drill during the third week of September. The plants are quite small going into the winter, but they have eight leaves and a reasonable root diameter and length, so they survive the winter without a problem."

This year's dry start to the autumn brought the trial drilling into line with farmers, most of whom were unable to use the earlier slot. The company's early-drilled trial went in on 20th August, just ahead of the rain because the ground was in Craig's words, "like concrete."

A late-sown crop can hold its own

NPZ UK's own trial data for the previous season points to late drilling not being a gamble. Last year, the late-sown plots averaged 4.68t/ha, against 4.37t/ha for the crops drilled on the usual date.

The difference, he says, is largely down to spring cabbage stem flea beetle larval damage.  

“Earlier-drilled crops, with the warmer soils, had on average about 20 larvae per plant; the late-sown plots escaped them,” he recalls.  

The company is feeding this and other information into the industry-wide OSR Reboot programme.

Why timing matters at the plant level

Craig points to NPZ funded research by Professor Ute Kropf of the University of Applied Sciences in Kiel into day-degree requirements to explain why a later-drilled crop develops differently.  

"Plants need around 150 day degrees to germinate and put out their first cotyledons, then roughly 120 to 150 day degrees for each pair of leaves," he says.  

"Once you pass about 1,000 day degrees the plant starts to differentiate, meaning that the flower buds begin developing.

“With an early-drilled crop it races through the differentiation stage, passing 1,200 day degrees quickly and moving into its reproductive phase.  

“That means that stem extension starts before the onset of winter. At this point differentiation stops and the maximum number of potential flowers is set.  

“After that, the reduction phase of these potential flowers begins. With plants focusing nutrients on lengthening the main stem, some potential tillers and buds are dropped before they can flower.  

“With a later-sown crop, 1,200 day degrees is not passed before winter sets in and bud differentiation carries on into the spring."

That, he adds, is where plant growth regulators have their part. "We'll apply them when the crop hits four to six leaves to hold the plant for two to three weeks," he says.

Vigour is the driver

"Varietal choice is really important when it comes to later drilling," Craig says. "You need a variety that will emerge rapidly in the autumn and continue to develop quickly through the season. Often these are hybrids but not all hybrids are suitable – some are bred for their performance in the earlier drilling windows."

On the Wolds in Lincolnshire, James Thompson farms 650 acres on a silty clay loam over chalk and has made late drilling a deliberate feature of his OSR system rather than a compromise.

"We would always avoid drilling until the end of the first week of September, so that the crop is being sown closer to some rain. We've never drilled in August," he says. "It has always worked for us."

Over the years James has tried many approaches to establishment. He has settled on leaving long stubble in the previous wheat crop, applying chicken manure and drilling with the Sprinter drill with 1” Dutch openers at 85 to 100 seeds per m2.  A companion crop with buckwheat and phacelia, distracts pigeons and flea beetles, as well as giving him a secondary source of income.  

“After drilling we roll twice, then it is about monitoring for slug and flea beetle predation,” he says.  

“We tend to go with foliar nutrition in the autumn; as soon as we’ve true leaves we’ll apply NKH Delta. In total our OSR crops get two foliar feeds to get them up and away as fast as possible.”  

The result, he says, is "a small and neat plant to go through the winter" – one that has never needed a PGR.

Vigour is what he looks for first in a variety.  

"I don't chase the latest variety. I find one that works well and stick with it, getting consistent results," he says. "I can't have a crop that wallows about, doing nothing for weeks. Vigour is my ultimate driver."

He has grown a lot of NPZ's Maverick over the last three years, valued for its rapid establishment and spring vigour, and says it is "near perfect" for his drilling dates.  

Trials on the farm, data in hand

James has run NPZ UK trials on his farm for three years and tests multiple varieties.  

"Trials are treated exactly the same as the farm crop," he explains. "We like to see how they perform on farm and the information we get back – the combine yield readings, the oil content. It enables us to make more informed decisions, because we see the plots and the crops on the farm."

Having grown Maverick, Valdez, Karat and Montana in last season's trial, he returns to the variety he rates best for his conditions.  

There is a less quantifiable benefit, too. "Ultimately, we enjoy doing it – we also get to meet a lot of experts and other farmers that we'd never normally get the chance to talk to. It can be a lonely industry at times, so it's good to see people."

Alongside the on-farm hosted by farmers like James, NPZ UK has two trial sites at Cambridge and Wisbech – with roughly 2,000 and 1,500 bordered 28 m² trial plots respectively.  

“This is where we do the majority of our UK replicated trials,” says Craig. “With minimum inputs, these trials are designed to reveal the performance of genetic traits.”  

The company also compares the effects of different dates and flea beetle tolerance through covered and uncovered plots.  

"We also draw on the results from northern France," Craig says. "Across the company we have more than 60,000 winter OSR yield plots, spread across 50 locations in 15 countries. It gives us unique and deeper insights into the varieties that we’re bringing forward to the UK market."