Reduce emissions with cover and catch crops

Incorporating cover and catch crops within a rotation to maintain soil cover during fallow periods can offer multiple benefits for soils, water quality, biodiversity and the farm business. These crops can also play a role in reducing greenhouse gas (GHG) emissions.

While the terms are often used interchangeably, they serve slightly different purposes:

• Cover crops ‘cover’ the soil between the harvest and establishment of main crops
• Catch crops ‘catch’ available soil nitrogen and prevent nutrient losses via run-off and leaching

Evidence shows that increasing the length of time ground is covered reduces net GHGs compared to systems where soil has limited ground cover. While outcomes can vary depending on cover crop species, management, and soil type, the broader benefits are consistently positive.

Cover crops contribute to soil carbon sequestration by adding organic matter when incorporated into the soil. Over time this increases soil organic carbon, effectively storing carbon from the atmosphere.

Organic matter is essential for healthy agricultural soils. It enhances biological activity, moisture infiltration and retention, and nutrient-holding capacity. 

Cover crops contribute to building organic matter while also playing a critical role in preventing soil erosion. 

They also reduce the risk of soil nutrient leaching. This not only improved water quality but also helps prevent indirect nitrous oxide (N₂O) emissions from when leached nitrate is converted.

Cover crops may act as ‘green manure’ reducing the need for synthetic nitrogen fertiliser in the following crop. However, the amount of nitrogen released for plant uptake is highly variable and depends on factors such as: species and biomass of the cover crop, destruction method, timing, soil and weather conditions.

Typically, 10–100 kg N/ha may become available in the first year of cash cropping after a cover crop, but this is difficult to predict accurately.

Cover crops are a multi-beneficial tool for improving both soil resilience and system sustainability, especially when integrated thoughtfully into a crop rotation.

Additional benefits include:

• Improved soil structure, enhancing root development and reducing compaction
• Better moisture management, by improving infiltration and reducing runoff
• Weed and volunteer suppression, by limiting light and space for unwanted species
• Increasing biodiversity, by providing habitat and food sources for beneficial insects and soil organisms
• Providing forage for livestock

While growing cover crops involves costs such as seed purchase, establishment, and destruction, the return on investment can come from:

• Stewardship schemes (when available): financial support may be available through agri-environment or sustainable farming incentive schemes, helping to cover cost of implementation
• Livestock feed: Certain cover crops can be used as valuable feed source, reducing reliance on bought-in forage
• Input savings: Long-term use of cover crops can reduce the need for fertilisers, herbicides, and soil remediation, improving soil health and lowering input costs over time

Cover crops are mostly sown:

• After an arable crop is harvested
• Over winter before spring crops
• Between harvest and an autumn-drilled crop
• Spring and summer-sown cover crops are also an option

Cover cropping isn’t straightforward in every farming situation:

• Heavy soils have higher levels of moisture in the topsoil which the crop prevents from evaporating
• Dry areas (where average annual rainfall is less than 500 mm) may see reduced storage of water in the soil and that means the yield of the crop that follows can be compromised
• Light, shallow soils with low levels of winter rainfall retain less water

There are a range of cover crop types that can be grown, either on their own or as a mixture:

• Grasses or cereal
• Brassicas
• Legumes
• Herbs, e.g. phacelia

Choosing the right crop depends on soil type, rotational conflicts, such as the carryover of pests and diseases​, timing and method of sowing and destruction. Seek advice on which might be best suited to your land type. 

Using a diverse mix can spread the risk of failure as some species might flourish in one year and others might not. Removing over-reliance on a single species reduces risk, particularly if a specific residual herbicide has been used on the previously grown crop and the cover crop variety is susceptible to it.

In every situation, ensuring that the crop can be sown as early as possible will maximise its growth potential.

Some growers will choose to cultivate the soil to prepare the seed bed after the previous crop has been harvested. Others will broadcast the seed – spreading stubble turnip seed into a standing cereal crop several weeks before harvest perhaps. This will allow the seedlings to establish earlier.

Cover crops require the same level of planning and attention as any cash crop to ensure successful establishment and long-term benefits. Establishment methods should be guided by cover crop choice, equipment and field conditions.

Cover crops can be sown by:

• Direct drilling into cultivated ground or stubble. Gives better species choice and establishment. In drilling, immediately roll the soil after sowing if it is dry enough as this will improve seed-to-soil contact, lock in moisture, and reduce the risk of damage from slugs
  
  
• Broadcasting into a standing or recently harvested crop can help extend the establishment window. The range of species to choose from is more limited if the seed is to be broadcast; with this method good levels of moisture are needed for seed germination