Or any other crop for that matter, otherwise they wouldn’t be producing such low yields. Disagree? Just look at the wheat yield below.
Source: SSC and DEFRA
OSR is generally drilled at too high plant populations which looks productive but as the plants are rammed in tight together they fail to branch out and don't produce much in the way of pods and seed.
When growers see a low plant population like we are experiencing this year the urge to disc it in and start again with a spring crop such as cereals, sunflowers, maize, soya or heaven forbid spring rape becomes overwhelming.
These low plant population crops could still produced a respectable yield given the right management and fair wind or at the very least not increase the level of expenditure.