At present, the weather is not allowing for field work on tillage farms. It is too wet to drive in fields and if it were dry it is too cold to spray. But these combined conditions allow for one job to be carried out – catch crop destruction.
While views will differ as to the timing of this job, the current spell of frosty weather provides an ideal opportunity to roll catch crops where timing is appropriate. Some will say it is too early to destruct a catch crop. Many will leave the crop there for as long as possible and this should be the aim. But where large amounts of biomass have been grown, knocking these crops now can help with breakdown and nutrient release for the following crop. The crop debris will still help protect the soil from erosion.
Crops which provide less cover than desired should be left to protect the soil for as long as possible. These crops should be easily incorporated.
Growers practising direct-drilling may sow straight into catch crops, leaving no bare soil at any stage in the production cycle.
Farmers who planted catch crops early in good growing conditions have good ground cover. Some growers may now want to reduce this level of biomass and to allow it to start to break down before cultivation.
Destruction by rolling
Rolling a catch crop in hard frost is one option available to farmers. Frost may kill off some of the species in a cover crop mix naturally, while others can be killed by rolling to break the stems when the crop is frozen. This needs to be carried out in a hard frost and it can reduce input costs.
This week, temperatures are forecast to go as low as -4°C, providing ideal conditions where appropriate. At these temperatures the ground is hard and easy to travel and plants are frozen and easily broken. However, it is important to get out in the early morning and complete the task before the thaw. Once the crop begins to thaw, the practice is less likely to work and the soil also becomes wet and sticky.
Where there are no problem weeds or large amounts of volunteers in a field, which could carry disease, then one run of a roller can leave ground ready for cultivation.
However, if there are problem weeds growing in the cover crop, these will need to be tackled with a herbicide. In this case a herbicide may be a more suitable method of destruction.
Roll and spray
Speaking to Philip Reck, the current chair of BASE Ireland who has a wealth of experience with catch crops, he noted that where there is a grass problem in a field it can be a good idea to roll the catch crop before spraying a herbicide to control the grass.
This practice means that the catch crop will no longer provide a canopy over the grass weeds, making them easier to hit with the herbicide following catch crop destruction. Less herbicide may also be needed after rolling as the bulky cover crop will be gone.
Philip noted that while rolling early can help to break down bulky catch crops and increase microbial activity, it may result in meadow grass returning, but again a lower rate of glyphosate should suffice to control this than would be needed if the cover crop had to be killed.
He added: “When a catch crop breaks down, it returns the nutrients that it has mopped up following the previous crop to the next crop in a plant-available form. Otherwise these may have leached to watercourses.”
Philip said that aside from catching the obvious elements like N, P, K and sulphur, the deep rooting of cover crop species draws under-appreciated but important nutrients, eg calcium for plant growth, from depth to the surface.
Frost tolerance in catch crops
It is important to remember that some plants in the catch crop mix are likely to die off in very hard frost as they are not suited to cold conditions. Crops such as mustard and buckwheat can be killed naturally by frost and may be well decayed before cultivation or sowing time.
Other species, such as many of the forage crops like forage rape or rye, can withstand frost. This is worth considering when choosing what to plant and what to do now.
Frost tolerance level of catch crops: