Cover Cropping – Helping Your Soil Biology

Ben Dolbear, Bright Seeds technical advisor and beef and arable farmer from the New Forest, looks at what cover cropping is, what its benefits are and the best crops to use.

The term ‘cover cropping’ envelops an array of crops, typically established in late summer and early autumn within a cereal rotation or between seasonal vegetable production.

The aim is to enhance the biology and fertility of your soil. Whether that is soaking up leftover nutrients from a previous crop or adding organic matter to the soil, making it more friable and easier to work with.

What Are The Benefits?

Cover cropping holds a number of benefits, with many closely linked to the five principles of regenerative farming –

  • Don’t disturb the soil – both physically and chemically
  • Keep the soil surface covered
  • Keep living roots in the soil
  • Grow a diverse range of crops
  • Integrate grazing livestock into your system

A winter cover crop will normally go in the ground between August and October. Generally, it follows a cereal crop that has been harvested in late summer such as winter wheat, winter barley or spring barley. The cover crop is then either terminated with glyphosate, or a crimper roller if in a hard frost. Alternatively, livestock can be used to graze off the cover crop or the crop can be incorporated into the soil the following spring. All three of these options are suitable depending on the farms infrastructure.

Another benefit of cover cropping is keeping live roots in the ground all year round. The soil structure and fertility improve considerably and, due to not moving the soil as regularly, there is less of the soil-caught carbon being released back into the atmosphere. Additionally, some cover crops have the ability to capture up to 85kg/ha of N, along with other important nutrients, and yield upwards of 35t/ha fresh weight biomass.

Furthermore, in the wetter months the fields aren’t bare, resulting in less leaching of both nitrogen and phosphate – this is advantageous to both the farmer and local environment agencies.

Although cover and catch crops used for green manuring can fit for everybody, it is vital to know what is wanted from the process and how they will fit into the farming cycle of each individual farm.

Things to watch out for

One of the most important things to consider when choosing a cover crop is what currently grows in your rotation. For example, if you have a cereal heavy rotation, planting cereal within a cover crop mix could result in further disease pressure or weed issues.

Likewise, if brassicas feature in a vegetable rotation, or oil seed rape in an arable rotation, then it would be wise to avoid them in a cover cropping mix due to the increased risk of club root.

A high degree of thought and planning should go into the machinery that is going to be used, and the practicalities of when you can establish your crop. Both of these factors can have an instrumental effect on the seed that is chosen to go in the ground.

What crops to use and where to use them

This is where a clear assessment of what you wish to achieve from the cover crop needs to be considered.

Legumes have their place within a cover crop mixture, with species like berseem clover, alsike clover and vetch used regularly. They develop their roots with bacteria nodules that have the ability to take nitrogen (N) from the air and convert it into a form that the crop can use. This can then be utilised by crops grown after the legumes – which will have been incorporated into the soil. Again, consideration should be taken if there are already legumes within the rotation.

There are also a number of popular non-legume species used for cover cropping. Although these do not fix N in the soil, they hold other benefits. Fodder radish/tillage radish is used for its deep-rooting, compaction busting ability. Whilst Mustard is very good for bulk growth and is a cheaper option. As with all brassicas, be careful not to sow it soon after, or within, a brassica crop due to the issue of club root. There are also specific fodder radish varieties that aren’t susceptible and don’t harbour club root, which can also be considered.  

Another option is to use shallow rooting species that produce fibrous roots, such as linseed, phacelia and buckwheat. These options help aid rooting in the ‘top’ soil zone. Remember, within cover crop mixes it is as much about the biomass under the ground as it is above.

Generally, the farms rotation and the desired result will map out where different types of cover crops should be used, though if a farm is on several different types of soil, this may help make the decision. For example, a farm that goes from chalk to heavy clay may want to consider different mixtures on the different soil types. It could mean the same mixture is used, but at an adjusted seed rate.

Seed rate is also adjusted depending on the time of establishment – with the later a crop is sown, the more seed is needed, and the earlier it is sown, the less seed is needed.

Is cover cropping becoming more popular?

The practise of cover cropping is nothing new, having been carried out for hundreds of years. The difference is that previously people didn’t realise it was happening. Traditional farming methods – with smaller mixed farms that always had crops in the ground, livestock spread around and less effective combining – were conducive to a regenerative farming type model.

In recent times, changing farming policy has brought more interest to these practises. Figures being published about carbon neutrality means many farmers are more aware of what they are doing and how they can give back to the environment – which does suggest a shift to cover cropping becoming more popular.

Lots of farmers and land managers have got an eye on getting themselves ready for ELMs (Environmental land management schemes). There are cover cropping options under current schemes such as SW6 – winter cover crops that are worth considering and can be very worthwhile.

There is also various funding from water boards who are increasingly paying farmers to cover the cost of seed, in an attempt to prevent nitrates and phosphates leaching into watercourses.