“If you’re home-saving it’s vital to understand what you are drilling. Putting 100 seeds on blotting paper in the airing cupboard is hardly ideal.”
Seed rates remain contentious for many growers, says Mr Munnery. Low rates intended to optimise populations and canopies and so boost yield can be “somewhat academic” if half the field fails because of slugs, flea beetle, pigeons or disease.
In that respect, hybrids’ generally lower seed rates make them more vulnerable than more “foolproof” conventional types, he maintains.
Much depends on thousand-grain weight, which can vary dramatically by year and seed lot.
Volunteers may also confuse the picture, especially for growers with tight rotations. “If you’ve grown rapeseed on a one-in-three rotation for 20 years, it’s likely some of your crop is volunteers. What that percentage may be is difficult to assess.
“Perhaps there’s a case for farmers to benchmark their crops by measuring how many seeds they drill and how many they establish.
“After all, if you have a large reservoir of tall volunteers there’s little point sowing a semi-dwarf variety.”