Cover crops are grown for different reasons, and this is important when choosing your mix, John Mahon of Teagasc told farmers at a recent Signpost farm walk.

John recommends a brassica such as forage rape and leafy turnip for livestock grazing, as early spring winter hardiness and a bulky crop are most important. He reminded farmers that if grazing cover crops, you must be out 4m from a watercourse.

For improving soil structure and increasing soil organic matter, the Teagasc advice is to choose deep rooting species such as tillage radish or mustard along with shallow rooting species such as phacelia.

If targeting grass weed control, the more open the crop the better in order to flush out as many weeds as possible from the seedbank, so open crops like mustard, phacelia, or vetch work well.

Rotation

The rotation needs to be kept in mind when choosing a cover crop. John advised against rushing into choosing a mix, and instead put thought into it before deciding.

If oilseed rape is grown on the farm, brassicas should be avoided for fields in oilseed rape rotation to avoid a build-up of clubroot infection.

“If you grow a lot of peas and beans, try and avoid the legumes and clovers in mixes.

“Likewise with oats. If you are a regular grower of oats, avoid anything with oats in it because you will build up oat mosaic virus and you could be 10 years trying to get out of that. Put thought into what is going into your mixes, keep your mixes simple. A two or three-way mix is an insurance that if one fails, you have something else.”

Sowing date

Sowing date has the biggest influence on the success of the cover crop sown, and sowing early is crucial in achieving good autumn growth. Cover crop sowing should be prioritised as soon as harvest is complete and straw has been removed.

With a late harvest on the cards for this year, John warned that it will be difficult and that farmers will be under a lot of pressure.

“Cover crops tend to go into spring barley ground and spring barley is going to be extremely late this year.”

He explained that the earlier cover crops are sown, the bigger the biomass. “Bigger biomass means more roots and a better chance of picking up on nutrients and preventing leaching.”

Concluding, he said to “put thought into it, talk to your agronomist or advisor on what mix might suit your farm best."