Spring weeding in organic cereal crops using a comb harrow is finished, except for one or two fields where stubborn patches of cleavers require later passes when the plants can be rolled up like spaghetti on a fork.
Comb harrowing is probably more of an art than a science. I always reckon that most of the benefit comes in releasing soil nitrogen through mineralisation and causing the crop to spurt in growth and be more competitive against weeds rather than the relatively small numbers of weeds that are actually tugged out of the ground by the tines.
I think you need a good reason to go through a crop more than twice. It also helps if the soil is as dry as possible – ideally powdery – to allow the tines to have greater effect. I make the last point even though it has been the least of my concerns for several springs, as once again, dominating high pressure systems over northern Europe means a dry spring.
The cereals don’t worry me too much at this stage, but for the clover leys, it’s a different matter. I’ve made two changes this year to prevent big seedling failures experienced previously during prolonged dry spells. I’m sowing a red clover/black medic trefoil/perennial ryegrass mixture, which trials on the farm show to be the most robust combination. I’ve also gone back to drilling the seed rather than broadcast-and-roll to try to get as much moisture as possible around the seed.
Clover seed is tiny and the seedlings easily give up and die if too little or too much water is present as they establish. In many regions, clover leys are best established in August, but being surrounded by a large vining pea operation rules this out as pea and bean weevil is rampant at that time.
FarmerFocusArable: Andrew Charlton