Assessing the need for cover crop solutions

Taking time to walk fields to assess soil health and plan suitable cover cropping remedies could pay even more than usual this season, says Helen Wilson of RAGT Seeds.

Many fields were badly affected by compaction last season and may still be suffering. A return to early drilling of cereals in some areas last autumn left little time for remedial work, which may have compounded the effect in some fields.

“Key indicators include areas of poor crop establishment and growth, as well as wet areas in fields, says Helen. “These are easy to spot during the winter, but many affected areas will still be visible from the sprayer cab so it is worth recording them for closer inspection after the crop is cut.

“On a rainy day it’s also worth spending some time in the office to check yield maps, soil maps and previous observations to help pull everything together to decide what to do.”

Vigorous roots

A cover crop of oilseed radish or mustard will put down vigorous deep roots that will drive through deep compaction and break up the soil. This alone may be enough to replace mechanical intervention if used on a regular basis. Cover crops need to be given time to work and can’t be used as a one-off solution.

If necessary, cover crops can also be used in combination with a suitable remedial cultivation, helping to maintain and develop soil porosity while raising organic matter.

“Ideally these crops need to be in the ground as soon as the combine has left the field as they require six to eight weeks growth to be effective,” says Helen.

“If you have brassicas, including oilseed rape, in the rotation, use a clubroot-resistant oilseed radish and avoid mustard.”

Having a mixture of rooting depths in a cover crop can often achieve more than using a single species. “Black oats, for example, provide a shallower, fibrous root system that improves the upper layers of the soil and helps remove excess moisture,” says Helen.

The above cover crop mixes can also be overwintered if the field is intended for spring cropping.

Nitrogen scavenging

If there are no obvious soil structure problems, fertility issues and pest presence may be responsible for poor crop performance.

Phacelia can be useful for scavenging nitrogen and releasing it back for the following cash crop. It should be sown by the end of August or the beginning of September.

Legumes can be used to fix nitrogen. Vetches and clover ideally should be sown by mid August to give them enough time to develop root nodules and fix sufficient quantities.

Pest control

Specialised high-glucosinolate mustard and oilseed radish varieties can suppress potato and beet cyst nematodes as well as lesser-known cereal cyst nematodes.

“If you see patches of cereals that are struggling for no apparent reason, it’s worth getting soils sampled to see whether nematodes might be the cause,” Helen advises.

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