Cut OSR seed rate to reduce establishment costs

Visitors to NIAB-TAG’s Morley Research Farm open day in Norfolk were urged to sow fewer seeds further apart and use robust agronomy to slash oilseed rape establishment costs, speed operations, boost yields and cut environmental impacts.

Agrovista’s Grow Crop Gold OSR project previously used a precision drill to show how sowing rape in rows 30cm apart, with 6.5cm between seeds in the row, could boost yields by more than 0.5t/ha over conventional min-til or plough-based techniques.

“But we’d be crackers to suggest people invest in a precision drill for oilseed rape, so we’re looking at achieving a similar result using more conventional equipment,” explained trials co-ordinator Niall Atkinson.

This year’s trials are seeking the optimum row widths and seed rates on seven UK sites, using a Simba DTX cultivator with Turbojet Wizard drill or Vaderstad Topdown with Biodrill to establish DK Cabernet, PR46W21 and dwarf type PR45D05 at rates of 15, 45 and 60 seeds/sq m, in rows 25, 50 and 75cm apart.

Seed rate is calculated per length of crop row to achieve target seed counts. At the lowest rates, plants now have stems “like tree trunks”, strong root systems and vigorous branching, so pods extend further down the canopy, so maximising yield potential.

“Oilseed rape sets its yield potential in November, that’s when floral initiation happens, which is why Aramo has a cut-off of nine true leaves or the end of November. So we need to avoid over-crowding then, which causes spindly plants, with pods limited to the top of the canopy, and many plants and branches carrying negligible pods, but still competing for light and nutrients,” he advised.

“I’d say as many as 90% of farmers use excessive seed rates. Aiming for 20-30 plants/sq m in the spring makes sense.”

Wider rows also mean inputs can be targeted at crop plants and withheld from areas between rows. Applying the maximum permitted field rate of nitrogen to the rows only could mean a saving on total nutrient input, so more can be used in spring, without exceeding N Max rules.

Alternatively, doubling the rate in the band could give the crop an extra autumn boost without exceeding the maximum field rate. “Either way you are putting the nutrient where it is required and not feeding weeds between the rows,” said Mr Atkinson.

Stewardship of key oilseed rape herbicides metazachlor and propyzamide could benefit too, suggested Agrovista technical manager Mark Hemmant. “If they could be band-applied to crop rows, with inter-row cultivation or glyphosate between rows, total usage could be cut, improving the chances of keeping such key herbicides available.”

But what about pigeons? Certainly, extra attention is required. “With fewer plants it is more important that every one survives, so the approach isn’t going to be well suited to fields surrounded by woods or where gas bangers are shunned due to a commercial shoot,” said Agrovista agronomist Selwyn Rees, who is based in Norfolk. But big, robust plants with strong root systems are better able to survive pest attack.

Agrovista would never advocate 20 seeds/sq m on farm, Mr Atkinson said. “Too much depends on the site, and 75cm between rows is probably a bit extreme, too. But I do think farmers could do more to reduce plant populations and boost yields as a result. Aiming for 20-30 plants/sq m in the spring makes sense. With OSR at £350-400/t, can you afford not to push for top yield?”

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