Self-seeding rapeseed as a catch crop: a risky choice
Considerations on the use of self-sown rapeseed as a catch crop should, unfortunately, start with the disadvantages, as these may predominate. The main argument against this solution is severe soil drying. Dynamically growing plants consume large amounts of water, and their high density prevents the root systems from developing deeply. Then, mainly the top layer of the field dries out, which poses a threat to subsequent plants.
Leaving self-sown rapeseed as a catch crop is not a good solution in fields where rapeseed often returns. Saturating the crop rotation with Brassicaceae species, both in the main crop and in the intercrop, is a direct path to increasing problems with pests such as brassica dry rot, clubroot, cabbage moth, ground flea beetles and snails.
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Catch crop for green fodder, silage or grazing
Destroy or leave?
As noted earlier, the use of self-sown rapeseed as a catch crop is allowed only in those locations where this species appears rarely, not more often than every 4-5 years. In such cases, rapeseed growing from spilled seeds can become a cost-free catch crop that will effectively protect the soil and can serve as a fairly good green fertilizer.
However, when leaving self-sown rapeseed as a catch crop, it is recommended to thin out the emergence of plants from scattered seeds by shallow cultivation of the soil surface. It is worth adding a legume, e.g. vetch or peas, to the rapeseed to increase the value of the mixture.
However, in crop rotations with a large share of brassicaceae, self-seeding rapeseed should be destroyed. This can be done by shallow cultivation, most often shallow discing, which mechanically destroys plants grown from spilled seeds. This procedure is usually performed two or three times. It is also possible to chemically destroy self-seeding plants using a non-selective herbicide. Before actual destruction, it is worth stimulating germination, e.g. with a mulch harrow.
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Sowing buckwheat after barley in July, i.e. two crops in one year 
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Advantages and disadvantages of catch crops
