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Raise yields with variable approach to growth regulators

Taking a variable rate approach to plant growth regulators applications can raise wheat yields. However, its uptake is being limited by current sprayer designs.

Crop protection is the next area that precision farming can have a real impact, believes Simon Griffin, head of science at precision mapping company Soyl. And as a means of getting more farmers interested, Soyl decided to look at plant growth regulators.

Lodging in wheat is caused by number of factors, including roots not being adequately anchored and stem disease. Importantly for farmers, it can prove very costly, reducing yields by up to 75%, as well as hitting quality.

Costs are also higher with the additional drying, which is estimated at up to $10/t. Plant growth regulators, therefore, have a key role in reducing risk by shortening the straw. However, most farmers apply plant growth regulators at a blanket rate.

Photo credit: Shutterstock

Photo credit: Shutterstock

That means plants with suboptimal canopies could be further stressed by being further restricted by a growth regulator, while plants with large canopies would benefit from a higher rate, he says. Therefore, matching rates to canopy size could reduce lodging risk. To test this, a trial was carried out in four fields in the UK, which have variable soils ranging from heavy sand clay to sandy loam.

Plant growth regulators

Satellite images were used to assess variation in crop biomass and growth regulators were applied either at a flat rate or variably with thinner areas getting less and thicker areas getting more. Rates of chlomequat and trinexapac-ethyl varied from 80% to 120% of standard rate. “One field saw a huge benefit with a much more uniform crop and less lodging.” Across the trial, the average yield increase was 0.4t/ha with the precision approach.

So why are farmers not doing variable rate growth regulators? Mr Griffin believes there are 3 reasons.

  • One limitation is the current kit, which restricted the amount the dose could be varied. “If we could use different equipment, we could have gone lower in some areas and higher in other and may have seen an even greater benefit.”
  • Another is tank mixing, as farmers are also applying other products.
  • The third is a culture of being risk adverse. Farmers are always going to be cautious and this is something that needs to be overcome.

One solution is to use a direct-injection system, allowing the mix to be varied across the field. A system is being developed at the German Institute for Application Techniques in Plant Protection.

A prototype sprayer has been developed that has shown to be accurate and the researchers believe this approach is now possible in field.

Oilseed rape

Oilseed rape is another crop that may benefit from a targeted approach with growth regulators, but more work is needed to refine sensor resolution. Even an oilseed rape crop with a small canopy with a green area index (GAI) of less than 0.8 will give a yield response (0.1t/ha) to a metconazole application in the spring.

A bigger crop with a GAI of 0.8-2 will see yield benefits of 0.2-0.25t/ha. Adas oilseed rape specialist Pete Berry says this shows why it is essential to manage the size of the canopy to maximise yields. In an Adas trial assessing nitrogen variability in a field, the researchers used an Isari crop sensor to map variations in crop biomass.

Dr Berry says the sensor could successfully predict when or not to apply a growth regulator. However, he adds it may be challenging for the system to detect smaller differences, which would allow small changes in plant growth regulator rates.

Both experts were speaking at the recent European Conference on Precision Agriculture, held in Edinburgh in July.