WITH seed rates playing a critical role in fulfilling wheat yield potential, growers should be thinking carefully about them when drilling wheat crops this autumn, is the advice from breeders, Limagrain UK.

But a blanket approach is not always best. Ron Granger, Limagrain's arable technical manager, acknowledged that getting seed rates right is complicated as it brings together a range of factors such as variety, drilling date, weather conditions, agronomic characteristics and importantly, experience of individual field performance.

“Get it right and there is the opportunity to fulfil that variety’s yield potential, but get it wrong and yield can be compromised from the very start. It’s all about attention to detail and really understanding the variety and the conditions in which that variety will be grown,” he argued.

This autumn we are looking at favourable establishment conditions and where sowing conditions are optimal seed rates could be adjusted considerably as germination and plant establishment will not be compromised.

“This does not necessarily mean increasing the seed rate. Using high seed rates with very high tillering varieties can have a negative impact on standing power, disease resistance and specific weight. If plant canopies are too thick, this will have implications on crop management,” he said.

How a variety behaves agronomically means it is important to build this into the seed rate equation. “Varieties differ in their tillering ability in the winter as well as how they hold onto those tillers in the spring – and this will, of course, affect final yield.”

Limagrain's seed rate trials carried out in 2018 in Essex showed these differences in a trial of five different varieties, drilled on October 11, 2017, at three different seed rates of 200, 300 and 400 seeds/m2 (see Graph 1). (Apart from the seed rates, all other agronomic inputs where kept the same.)

“In what was a challenging year weather-wise, the results were surprising. It could be assumed that higher seed rates would produce higher yields, but this was not necessarily the case”

“We found that a higher tillering variety, like LG Sundance, was highest yielding at the lowest seed rate of 200 seeds/m2, producing a yield of more than 10.60 t/ha. The yield potential dropped at higher seed rates, reflecting results we have seen with LG Sundance in previous seasons," he pointed out.

“What this translates to on-farm, is that growers should consider lower seed rates if planting LG Sundance before mid-October, to maintain optimum yields from the start. Looking at LG Skyscraper, which has similar tillering and spring development to Evolution, it yielded best at 300 seeds/m2, with a yield of more than 11.50 t/ha.”

LG Jigsaw and LG Spotlight are high tillering varieties and again the data suggests that these varieties perform well at lower seed rates – although the differences are subtle.

A similar seed rate trial in Glenrothes provided important regional data sets for LG varieties. “Historically, in the north, seed rates are higher to compensate for more erratic weather conditions. We wanted to investigate if this is still necessary and if there are sufficient yield benefits as ultimately, growers want crops that will not only yield, but are still standing at harvest,” he added (see Graph 2).

LG Skyscraper yielded a massive 13.4 t/ha when drilled at 300 seeds/m2, but when drilled at 400 seeds/m2, this dropped to 12.3 t/ha – confirming that high seed rates don’t necessarily bring higher yields.

This was also the case with LG Spotlight and LG Jigsaw which produced the highest yields at the lower seed rate of 300 seeds/m2, and showed yield penalties at the higher seed rate of 400 seeds/m2.

“These are significant penalties in yield and support the theory that high seed rates are not always the best way of achieving high yield potential, but again growers have to weigh up the risk associated at the time of drilling to ensure good crop establishment,” said Mr Granger.

“There is always some room for movement. Wheat is a pretty robust crop and will produce more tillers if required, or drop tillers if the spring weather dictates, such as in a drought situation. But getting the seed rate as close to the optimum as possible gives your crop the best chance of achieving maximum yield potential, as well as making it easier to manage throughout the season,” he said.