Fresh clues as to why UK oilseed rape yields remain stubbornly static despite breeders’ steady stream of new, potentially more productive, varieties emerged at the HGCA & PGRO Oilseeds & Pulses conference.
Two fungi hitherto undetected in long-term rotation trials at The Arable Group had been picked up during work by Warwick University researchers examining the plants’ rhizosphere Ð the area immediately around the roots, noted TAG’s Ron Stobart.
One, Olpidium brassicae, accounting for about 10% of the total, looked especially interesting, said Mr Stobart.
“It’s known to be a pathogen of other brassicas. It doesn’t produce any foliar symptoms, but it’s known to affect roots, and its resting spores linger around in the soil for 10 years plus.”
The other previously absent fungus was a species of Pyrenochaeta, he noted. The “bolt-on” WU work found that concentrations of a wide range of fungi was markedly different after three wheat crops following oilseed rape compared with those after continuous rape.
After six years of an eight-year series of large plot replicated rotational trials growing Winner under local best practice to avoid varietal confusion of the results, it was clear that intensive rape cropping brought yield penalties, Mr Stobart explained.
The average yield from “virgin” land was 3.9t/ha. Growing the crop one year in three gave 3.55t/ha, and alternate cropping with wheat produced only 3.39t/ha. “It’s quite a steady quantifiable drop-off,” he said. But while overall oil output clearly declined, there was no indication that oil content itself was affected by more frequent cropping.
All sowings received two fungicide treatments, but stem canker was only half as severe in crops on virgin land as the others. And there were signs that plants on clean land tended to have deeper tap roots.
The work also found that a significant proportion of the final populations in the stands away from virgin land consisted of volunteers.