Delayed nitrogen could raise yield

Oilseed rape yields could be increased by about 0.5t/ha by applying late foliar nitrogen and other micronutrients, according to Strutt & Parker.

Many crops typically receive 200kg N/ha in two splits, but delaying 20kg of this until late petal fall could keep pods green for longer and ultimately boost yields, says the firm’s agronomist, Jock Willmott. “Rape can be very fickle in how it responds to nitrogen and it can be difficult to achieve the maximum efficiency from everything we’re putting on.”

For the past three years, Mr Willmott has been involved with late foliar nitrogen field trials on a 930ha farm near Luton, Bedfordshire. “We’re not looking to reduce the total amount of nitrogen applied, at this stage it’s more about getting the most yield out of the same rate of nitrogen.”

Last season, 180kg N/ha was applied in two splits during February and March, and the remaining 20kg went on as a late foliar application of Omex’s Oilseed Extra at various timings and dilutions The highest yield (5.16t/ha) came from applying Oilseed Extra at the recommended 100 litres in 200 litres of water at late petal fall. This gave an extra 1.09t/ha over the untreated area, which only received a total of 180kg N/ha.

Attention to detail

“Generally we’d hope to get a 0.4-0.5t/ha yield increase, which more than outweighs the cost,” says the farm’s manager, Andrew Robinson. “But you can’t just bang it on and expect to get that. Everything else has got to be right, from the establishment and canopy management to what fungicides you use. Attention to detail from start to finish is crucial.” Land is tested for soil mineral nitrogen and oilseed rape tissue analysis for nitrogen and sulphur is also carried out each season.

Mr Willmott says the product used in these trials also contains a mix of micronutrients, including magnesium, copper and zinc, but he thinks delaying the nitrogen has the most significant effect on yields. “Last year we did see a benefit in oil quality, which may be due to the extra micronutrients.”

Potential problems
Scorch can be a problem when applying late liquid nitrogen, but Mr Robinson says keeping to the recommended water rate of 200 litres/ ha and avoiding spraying in strong sunlight reduces risk considerably. “You’ve got to use some common sense. Most of ours is sprayed in late evening or early morning.”

But while keeping water rates up reduces scorch risk and enables the product to reach lower pods and leaves, it does present a logistical problem due to the large total volume (300 litres/ha) you are applying, he notes.

He does not think crop damage is a major issue, despite the advanced state of many crops at flowering, as all of his spraying is done using a self-propelled sprayer.

“But if you’re using a trailed sprayer behind a tractor, you could do more damage going through the crop at this late stage.”

Mr Robinson also acknowledges that keeping the pods green presents problems with later ripening and says pre-harvest desiccation with Roundup (glyphosate) is essential. “Last year we started cutting rape about two weeks later than the earliest land around here. But we don’t mind if yields make up for it.”