New studies confirm superior OSR nitrogen stress tolerance

The superior nitrogen stress tolerance of two of the latest high reliability Dekalb hybrids has been confirmed in the company’s most recent restricted-fertilisation trials.

The replicated 2020/21 trials undertaken with four top-performing TuYV-resistant EX and competitor hybrids showed mean gross outputs falling from 4.84t/ha to 4.61t/ha when nitrogen applications were cut from 180kg/ha to 140kg/ha – an average gross output reduction of 0.23t/ha. This resulted from an average reduction in yield of 0.25t/ta coupled with a 0.7% increase in oil content. Both widely-grown DK Excited and RL candidate DK Exposé, however, lost less than half this gross output at 0.09t/ha and 0.11t/ha respectively, and a quarter that of the 0.44kg/ha lost by the variety least tolerant to nitrogen reductions (Figure).

Figure:  Average gross output reductions from cutting nitrogen applications to four                TuYV-resistant varieties from 180kg/ha to 140 kg/ha

Source: Dekalb two-site trials in 2020/21

In showing this superior tolerance to nutrient stress, they follow in the footsteps of a number of Dekalb hybrids introduced since DK Exception – the first variety to emerge from the breeder’s restricted-nitrogen development programme in 2016.

“Almost a decade ago when our breeders set out to develop OSR varieties combining the highest possible output under optimal nitrogen levels with the least output penalties when N supply is constrained, their main aim was to improve the crop’s resilience to seasons in which conditions limited nutrient availability,” explains Dekalb trials specialist, Richard Williams.

“The impressive powers of hybrids, in particular, to cope with stress has long been appreciated. But only by restricting nitrogen supply on a number of Dekalb breeding sites from 2013 did the extent to which hybrids differ in their ability to tolerate nutritional stress really become apparent. “As well as promising greater resilience to increasing seasonal weather extremes, of course, varieties losing the least output at lower levels of nitrogen supply will be especially valuable for growers in a future in which N prices are as high as they are set to be for the coming year,” he observes. “After all, even at an ammonium nitrate price of £650/t, the £26/ha saved by a 40kg/ha cut in nitrogen application is more than twice the loss in income of the 0.1kg/ha average reduction in gross output of our two most tolerant varieties at 2023 harvest futures values.”

Much of the superior environmental stress tolerance the Dekalb programme has built into its hybrids over the years is considered to be related to their greater branching ability, in general, and branching from low down the stem, in particular.

“The fact this ability can only be fully exploited where plant populations are not too high underlines the need for especially carefully control over seed rates to make the most of this extra resilience.” Mr Williams stresses.

“All the more so with earlier sowing, which offers greater opportunities for spring N savings through better establishment and GAI development anyway, and for which both DK Excited and DK Expose are some of the best-suited varieties.”