Use cover crops or green manure
Find out how land managers can use cover crops and green manure to improve soil health and reduce erosion and runoff.
If you’re completing this action as part of the Sustainable Farming Incentive pilot, how you do it is up to you.
The advice on this page can help you get better environmental and business benefits, but you do not have to follow it to get paid.
About cover crops and green manure
Cover crops are grown over a single winter. They cover bare soil and stubble left by cash crops like maize and cereals.
Plants suitable for a cover crop are:
- cereals and grasses
Cover crops are not harvested like cash crops. Instead, you destroy them with herbicide, rolling, ploughing or frost ahead of the new crop.
Green manure is a type of cover crop. You can keep it for longer periods, like a whole cropping year. This allows it to fix (take from the air) additional nitrogen in the soil. Green manure is ploughed into the field while still green.
Benefits of cover crops and green manure
Cover crops and green manure will add organic matter to soil. This improves soil structure and helps it absorb and keep in water. This means:
- ground conditions will improve, so farm operations are possible for longer
- you can reduce tillage and irrigation costs
- soil will retain more nutrients
- you’ll reduce the risk of soil erosion, as the flow of water into water bodies and watercourses is slowed
- you’ll increase beneficial microbes that will provide nutrients to the next crop
- the number of earthworms can increase in the soil, which helps prepare seedbeds and reduce disease organisms
You can reduce soil erosion and runoff using cover crops and green manure over bare ground in winter. This means:
- fields do not lose fertile topsoil and nutrients, like nitrogen and phosphorus
- water is cleaner, as less soil, pesticides and nutrients reach water bodies and watercourses
- you can reduce use of artificial fertiliser, as you’ll increase soil fertility
- you’ll stop nitrogen leaching, keeping nutrients in the soil for the following cash crop
- more water is available for crops, as it infiltrates the soil more easily
- there’ll be a lower risk of flooding, as the flow of water into water bodies and watercourses is slowed
Cover crops and green manure can reduce the use of pesticides and herbicides. They:
- create habitats that support natural predators of pests
- can grow fast and smother arable weeds, like black-grass
- improve soil structure, which prevents wet and compact soils favourable to weeds
You can increase the benefits to soil of cover crops and green manure by combining them with:
How to use cover crops or green manure
Use a soil risk assessment to identify issues that cover crops or green manure can resolve. Issues include:
- poor soil structure, like compaction
- soil erosion and runoff
- low levels of nitrogen in the soil
When you identify the purpose of your cover crop or green manure, you can maximise the benefits when you use them throughout your rotation. Where possible, aim to use a cover crop on the same field within the rotation 2 out of every 5 winters.
Cover crops may continue to benefit the soil 2 years after they are destroyed. This can vary and depend on how you manage soil across the farm. The ideal is to use them in a rotation on a long-term basis.
You’ll have most success where you can grow an even ground cover, as this will produce the highest amounts of biomass.
Consider how you’ll destroy the cover crop. Avoid tillage where there are historic features and disturb the ground as little as possible.
What seeds to sow
You must use organic seed if you farm organically or are converting to organic farming. You’ll need approval from your organic certification body to use non-organic seed.
When choosing a seed mix, make sure you can sow all varieties at the same time and to the same depth. This will give you even germination and widespread cover.
Get advice from your seed supplier on the best seed mix to suit your land and local conditions. The choice of seeds will depend on the issues you are trying to resolve.
To reduce soil erosion and runoff, find out how to cultivate and drill across slopes.
Cereals and grasses
Suitable cereals for cover crops and green manure include:
- black oats
- forage rye
- winter triticale
Suitable grasses for cover crops and green manure include:
- Italian ryegrass
Cereals and grasses:
- grow quickly and provide good ground cover
- are easy to establish and manage
- will germinate in cooler weather
- are good for increasing soil organic matter
- can be grazed
Black oats release toxins when destroyed, which can help control some pests.
You can use legumes in either cover crops or as a green manure. They’re better in green manure as you keep them in the ground over the growing season. This allows them to fix nitrogen in the soil.
To reduce black-grass you can grow a 2 year sown legume fallow.
Suitable legumes for cover crops and green manure include:
- vetches, like common vetch and hairy vetch
- clovers, like red clover, white clover, alsike clover, sweet clover and crimson clover
- black medick
- peas and beans
- grow slowly and need warm conditions to germinate and establish
- fix nitrogen over the growing season and increase soil fertility, reducing the need for fertiliser
- will improve soil structure
- boost beneficial fungi, which improves soil health
- provide a source of pollen and nectar for invertebrates
- can be undersown into a cash crop so they can establish early in warmer conditions
Suitable brassicas for cover crops and green manure include:
- mustards, like yellow mustard and brown mustard
- oil radish
- tillage radish
- stubble turnip
- usually need warmer conditions to germinate, but can establish and grow quickly in the autumn
- are deep-rooting and good at breaking up compacted soil
- are normally cheaper to buy
- rapidly release nutrients to the following crop
Varieties of mustard will:
- grow quickly and give good ground cover
- release toxins when they’re destroyed, which can help control crop pests like beet and cyst nematodes
Oil radish, tillage radish and stubble turnip are not suitable to prevent soil erosion and runoff. On land with high risk of runoff and soil erosion choose cover crops with more ground cover.
You can graze some brassicas, like stubble turnip and tillage radish. This is best suited to flat, free draining land with low risk of runoff and soil erosion.
Do not use grazing to destroy a cover crop. You can use grazing to prepare a cover crop for other destruction methods.
Suitable herbs for cover crops and green manure include:
- usually need warmer conditions to germinate
- are often cheaper to destroy, as they are killed by frost
- provide a source of pollen and nectar for invertebrates
- control weeds
- capture high amounts of nutrients in the soil, for the next cash crop to use
Prevent a green bridge
Pests and diseases can survive over winter on a cover crop (a ‘green bridge’). Choose a cover crop that does not support pests and disease that will affect the following cash crop.
To avoid a green bridge, do not sow:
- legumes in a cash crop after legumes in a cover crop or green manure
- potatoes or wheat after a cereal cover crop
- a cereal cash crop after a cereal cover crop
- a brassica cash crop after a brassica cover crop
Herbs do not create a green bridge, as you would not typically grow them as a cash crop.
How to establish cover crops or green manure
When to sow
Establish cover crops and green manure as soon as possible after the previous cash crop. This is usually in late summer or early autumn. If you’re in an area with a shorter growing season, you may need to choose plants that germinate and grow in cooler weather.
You can establish cover crops and green manure after a late-harvested cash crop on light soils. In these situations, it’s best to oversow the cover crop into the cash crop. You’ll need a higher seed rate when you oversow, for a better chance of establishment.
On heavy soils it’s not possible to establish a cover crop or green manure after a late-harvested cash crop.
For the introductory level of the arable and horticultural soils standard, establish green cover by mid-October. For the intermediate and advanced level of the standard, establish green cover by the end of September.
Sow your cover crop or green manure
You can drill or broadcast (scatter) the seed mix. Drilling seeds is more reliable than broadcasting. The germination success is higher, but broadcasting is cheaper.
If available, you can use:
- equipment with multiple hoppers to sow different sized seeds
- equipment that can drop seeds at different depths
This makes sure seeds are sown evenly. If you do not have this equipment, mix seeds in the hopper between drilling periods. This will help to reduce competition.
Roll after drilling or broadcasting to:
- keep in moisture
- ensure good seed-to-soil contact
- reduce slug damage
You can add up to 30kg per hectare of nitrogen if:
- cover crops and green manure need help to establish
- the main aim of the cover crop is to add organic matter
This can help to produce the highest amounts of biomass in the cover crop or green manure.
You do not need to add nitrogen if you:
- want to stop nutrients leaching
- regularly use cover crops or green manure in your rotation
- have established a cover crop or green manure on the field early in the year
- are fixing nitrogen with legumes
More ground cover and organic matter can cause slug populations to increase. Regular use of cover crops and green manure will also increase the populations of natural predators of slugs. Try to avoid controlling slugs to allow the natural predator populations to build up.
You must follow the farming rules for water. These require you to take steps to stop manure, fertiliser or soil getting into water bodies and watercourses.
How to destroy cover crops or green manure
Destroy cover crops and green manure at least 3 weeks before establishing a cash crop. You can destroy winter cover crops more than 3 weeks before a cash crop if you want to:
- warm the soil for the next cash crop, which can speed up germination
- reduce the risk of pest or disease transfer between the cover crop and cash crop
- reduce any toxic effect of the cover crop on the cash crop
You can destroy cover crops using:
- rolling or crimping
The method you use will depend on soil type, crop type, weather and the risk of soil erosion and runoff. Avoid using machinery on wet soils as this can cause soil compaction.
A frost is likely to kill:
- all herbs
- brassicas like mustards (white and yellow), oil radish and stubble turnip
It’s less likely to kill legumes and cereals.
This is a low-cost method, but it:
- reduces the range of plants you can use
- can leave soil bare over winter if there are early frosts
- can leave the crop alive if the winter is mild
Rolling or crimping
You can use rollers or crimpers on cereals. They damage and flatten plants without disturbing the soil. Rolling or crimping will only kill cereals when they are producing ears.
You can use rollers or crimpers with reduced herbicide application. This will produce the same results as a full rate of herbicide application.
Check if you can get funding for new cover crop management equipment.
Herbicides are one of the easiest and most cost-effective ways to destroy a cover crop. Herbicides based on glyphosate are most common.
Avoid excessive contact with the soil, as glyphosate may negatively affect beneficial fungi in the soil.
Ploughing is a reliable method to kill a growing cover crop.
Ploughing can undo some of the benefits that the cover crop has provided, as it disturbs the soil. It can damage worms, fungi and other life in the soil. It can also weaken soil structure, increasing the risk of:
- soil erosion
After a cover crop, ploughed soil has a better structure than ploughed soil that has not had a cover crop.
Do not plough on land with historic features like earthworks. You must only use direct drilling (no-till) cultivation.
Use grazing to prepare for other destruction methods
You can graze your cover crop, but do not use grazing to kill a cover crop. The high levels of grazing needed to kill the plants will cause soil compaction, leaching of nutrients and runoff. Grazing also reduces the amount of organic matter that the cover crop adds to the soil.
Grazing can prepare the cover crop for other destruction methods and help to control weeds, like black-grass.
Before you graze livestock, make sure the cover crops you use are not poisonous to livestock
What cover crops or green manure should look like
You’ll see a well-established crop that produces large amounts of biomass above and below ground.
- better cash crop growth and improving yields as soil health improves
- more organic matter in the soil
- easier cultivation as soil structure improves