In winter the soil is ploughed every year and then selective herbicides are used to destroy any wild plant species that manage to germinate. but around the edges of the crop, where the herbicide spray doesn't quite reach, and where there is more light and less competition with the wheat, a select assemblage of annual arable weeds often persists. There presence in arable fields is as old as agriculture itself.
Corn poppy Papaver rhoeas depends on the plough to bring its tiny buried seeds to the surface, exposing them to the light that they need for triggering germination. Most scatter their seeds from their pepper pot seed capsules long before the combine harvester arrives.
Field pansy Viola arvensis is a frequent annual arable seed of crop edges. Its dome-shaped seed capsules split into three boat-shaped segments. They immediately begin to shrink as they dry in the sun, squeezing the seeds - which as smooth and slippery as wet soap - until their are fired out into the surrounding crop.
Most of these arable weeds have small flowers, nonetheless beautiful when you take a close look. This is cut-leaved cranesbill Geranium dissectum. Its tiny flowers are attractive but .....
.... its fruits are exquisite too. Here they are, ripe and ready to go - five seeds each in their own capsule, attracted to a strip of tissue that runs right to the tip of that beak-shaped structure. It becomes as tense as a clock spring as it dries, until the capsules break free and are flicked upwards, hurling out their seeds like a medieval siege catapult.
After the seeds have been discharged the fruits remain attached to the plant, like miniature chandeliers.
Most of these small arable weeds have no impact on crop yield, but sometimes more serious agricultural weeds survive and can become a problem - this is wild oat Avena fatua, whose seeds have a remarkable ability to drill themselves into the soil, which you can see by visiting this post.
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