Ultimate Guide to Cover Crops
Why grow cover crops?
There are many important reasons why cover crops should be sown and utilised, despite the greening rules being scrapped from next year. Using a range of species and crops for different lengths of time, can create significant benefits for soil health. This is a non-exhaustive list of reasons why cover crops are beneficial:
· Nitrogen fixation – particularly key with input prices and availability in the current season.
· Reduced leaching of nutrients, valuable for the next crop as well as environmental benefit. Crops that can fix nitrogen or store any excess nutrients, and then release this back into the soil for future crops adds to the following crop.
· Improved soil organic matter content, incorporating the green manure. This adds to the friability of the soil and is great for increasing worm numbers, which only adds to the benefit of the soil.
· Better soil structure, using a range of species with different rooting depths can create drainage channels and break through soil pans. This can also be beneficial in holding lighter soil structures together and reducing soil erosion.
· Weed control, a lot of the species used produce masses of biomass which can supress weeds coming up. Some species also have allelopathic qualities, further helping with reducing weeds.
· Reducing soil compaction, through the root mass produced, as well as the deep rooting species. Using varied rooting depths will be a further benefit to this.
Nitrogen costs- improves yield without artificial input
Nitrogen in the form of N2 is fixed by rhizobium bacterium on the nodules of legume cover crops and this nitrogen will be freely available upon destruction and incorporation of the old cover crops. This freely available nitrogen can improve subsequent yields and reduce the need of purchased-in artificial fertiliser, thereby improving gross margins of any crop grown after a cover crop.
Reduced leaching and run off- environmental impacts/ protecting our countryside good farming practice
One of the greatest pollutants from agriculture is diffuse source pollution, which can arise from both nitrate leaching and soil run-off which deposits phosphates into surface waters in the UK. Both nitrates and phosphates in surface waters cause detrimental effects to local water sources, such as eutrophication which causes excessive algal blooms that reduce oxygen levels in the water and therefore reduces biodiversity in surface waters. Nitrates leach over winter when winter rainfall washes out nitrogen in bare soils not covered by a crop, whereas phosphates, which are bound to soil particles are deposited into surface waters by soil erosion. This is most prevalent in soils which have poor soil structure. You can help reduce these pollutants on your farm by planting a cover crop which will scavenge for leachable nitrates and help bind the soil thereby preventing further phosphate deposition in your local water.
Organic matter/ climate change and carbon sequestration
Asides from preventing soil erosion and phosphate enrichment of local surface waters, the beneficial effects of cover crops on your soil structure includes the building up of soil organic matter. Soil organic matter is the organic fraction of the soil, formed from decaying organic material such as vegetation and animal deposition. The carbon from the decayed vegetation is stored as complex carbon chains which forms organic matter. These carbon chains are often depleted by heavy tillage systems in arable farming and consequently the average arable farmer in the UK may only be achieving 1-2 % organic matter. By growing cover crops and incorporating into your soil, you are helping to reduce your farms carbon footprint as you are capturing the carbon otherwise released to the atmosphere into the soil.
As well as reducing the amount of carbon in the atmosphere, soil carbon sequestration can also improve soil health and its ability to retain warmth, moisture, and fertility; all of which are conducive to crop growth. A study by Defra found that, where soils were as low as 1% organic matter, cereal yields could be as much as 5% lower than soils containing 4% organic matter; implying that the building of soil organic matter is linked to yield.
Better soil structure
Cover crops which have vigorous rooting such as black oats and forage rye help form good aggregates within the soil, opening pores for free movement of air and water which is good for crop growth. Other species, such as tillage radishes have extremely strong tap roots which can break up compaction in soils thereby reducing the need for expensive machinery passes to break up the compaction. Using a mix of species with different rooting types enables soil structure to be improved across different depths.
Weed control
As outcompeting weeds is a well-known cultural control of weeds, growing a cover crop can form an integral part of an Integrated Weed Management programme. Certain species, such as White Mustard, Forage Rye and Berseem Clover are very vigorous at growing and therefore outcompete and suppress weeds. This natural suppression in weeds can lead to reduced herbicide use which is better financially and environmentally to the farmer. Other species, such as Black Oats may have some allelopathy effect on weed growth. Allelopathy is the secretion of natural chemicals by one plant to inhibit the growth of another.
When to sow?
· There are a wide range of sowing dates, dependent on what the cover crop is going to be used for.
· Most species will need to be sown by September to have established well enough before winter.
· Late sown species such as Rye can go in as late as October - this is ideal for following maize harvest
What to sow?
Phacelia
Phacelia is very quick to establish and will mature in 10-12 weeks after sowing. It will produce a large, shallow root mass, making it useful for improving soil structure and organic matter in the soil, as well as preventing leaching. The biomass it produces also acts as a weed suppressant too. Once mature and in flower, it is a great attraction to bees and other pollinators. It can be used if OSR is in the rotation. Not winter hardy.
Suggested sowing rate – 10-15kg/ha
Sow April – October
Vetch
From the legume family, vetch is very suitable for fixing nitrogen, even in a relatively short space of time or even at low temperatures. It works well as a companion to Rye. Winter hardiness depends on variety but will break down quickly once incorporated. It can offer some effectiveness at weed control with the biomass produced. Will add protein to ruminant’s diet if used for grazing after
Suggested sowing rate – 50kg/ha
Sow March - October
Red Vetch
A slightly more frost susceptible option to either Spring or Winter Vetch, that will produce plenty of biomass in a short space of time.
Suggested sowing rate – 50kg/ha
Sow March - October
Mustard
White mustard is typically used in most situations as it is quick to establish and will produce a good amount of biomass. This makes it excellent at preventing leaving and controlling weeds. It can improve soil structure and build organic matter, but it is not winter hardy. Sown after cereals, mustard can be grazed from October/November. Brown mustard is used in situations where a biofumigant is needed and is more winter hardy.
Suggested sowing rate – 10-15kg/ha
Sow April – September
Radish
Broken down into two main types, there is the oil radish and the tillage radish. They are great for improving soil structure and reducing compaction. The have large amounts of biomass, which acts as a great weed suppressor and improves the soil organic matter. With its quick growth habit, it quickly produces a large leafy canopy, which can be incorporated back into the soil, enhancing soil structure and enriching soil humus
Oil radishes grow quickly, with a widely branched root system, penetrating deeply into the soil profile. This attribute aids the radish’s ability to scavenge for nitrogen, preventing leaching, allowing nitrogen to be recycled into the following crop.
Oil Radishes can be further broken down in to three types, Classic, Type 1 and Type 2. Types 1 and 2 have some degree of nematode control, with Type 2 being the most effective.
Tillage radish produces a long tap root, penetrating through many different soil’s types and profiles, improving drainage and air movement through the soil. This deep tap rooted radish captures and stores nutrients from deep within the soil which is released during the spring for the next crop. Very effective at relieving soil compaction.
Suggested sowing rate – 10-25kg/ha for Oil Radish & 10-15kg for Tillage Radish
Sow April – August for Tillage Radish, April – September for Oil Radish
Rye
A quick growing option that is fantastic for preventing leaching and scavenging nutrients, particularly Nitrogen. Even at low rates, rye is great at supressing weeds and will help improve soil structure. Forage rye can be sown as late as October and is winter hardy. It will provide early grazing in the spring for cows or can provide over wintering for sheep.
Suggested sowing rate – 30-50kg/ha
Sow August - October
Black Oats
Deep fibrous roots on black oats make the suitable to improve soil structure and relieve compaction. Black oats also contain allelopathic qualities, which help with the suppression of blackgrass germination. It can be sensitive to frost but able to be sown up until October.
Suggested sowing rate – 30-50kg/ha
Sow August - October
Berseem Clover
An annual legume that is quick to establish. It is great for nitrogen fixation but is not very frost tolerant. There are significant varietal differences, Tabor, which is a single cut type with no regrowth after.
Suggested sowing rate – 15kg/ha
Sow March – August
Crimson Clover
A great weed suppressant, producing plenty of biomass (more than that of red clover) that will grow at lower temperatures to other legumes. It has a very upright growth habit and degrades into the soil quickly after destruction, releasing nutrients for the following crops. It is also very attractive to pollinators.
Suggested sowing rate – 15kg/ha
Sow August - September
Buckwheat
A very fast growing species that is good at mopping up excess nutrients in the soil, particularly phosphates. Not frost tolerant and will break down quickly once incorporated. Shallow roots are produced but plenty of about ground biomass.
There are no wrong answers when it comes to putting a cover crop in, each situation might vary, which is why a mix is often the best way to go. Each species has its own benefits that can improve the soil.
Cover crops can be a post-harvest catch crop, an over winter cover or just around field edges for attracting beneficial insects or wildlife in areas that are not being cropped.
New Bartholomews Mixes
From our successful trial in autumn of 2020, we have put together some new mixes to add to the existing selection we offer.
Soil Erosion Mix
50% Black Oats
3% Phacelia
10% Buckwheat
25% Oil Radish
12% Crimson Clover
This mix was designed with the idea to focus on holding the soil together with species that have good and variable rooting depths.
Brassica Free Mix 1
15% Vetch
5% Crimson Clover
80% Rye
Brassica Free Mix 2
3% Phacelia
25% Buckwheat
25% Berseem Clover
47% Vetch
Seeing more brassicas in rotation there is increased demand for cover crop mixes that don’t include them in. these two have been designed to still hold the key benefits of growing a cover crop, but without the brassica element.
Beneficial Insect Mix
15% White Mustard
50% Rye
5% Crimson Clover
5% Berseem Clover
25% Buckwheat
A quick growing mix, that will be beneficial to insects and improves the soils.
All mixes above are sown at 25kg/ha .
Why use a cover crop mix?
Mixes are a great way to maximise the individual benefits of the species.
Using species with different rooting depths and growth habits offers the most advantages, improving the soil for future.
Choosing a mix or even an individual species should be decided by what you want to achieve – for example relieving compaction or reducing nutrient run off. Other crops in the rotation should also be considered, as volunteers or species in the same family could cause problems.
Suggested Mixes:
Rye/ Vetch
Typically, at 80/20 ratio.
Ø Rapid establishment, offering the ability to cover ground and supress weeds.
Ø Deep rooting for relieving compacted soils
Ø Suitable for grazing
Ø 35-70 kg / ha depending on conditions and soil type
Soil Improver
Ø Fast to establish
Ø Root structure covers different levels of the soil profile
Ø Retains moisture for the following crop
Ø Contains: Winter Oats, Mustard, Oilseed Radish & Phacelia
Ø Sow at 40-50kg per ha in August/September
Oat /Vetch
This mix comes in 70/30 ratio.
Ø Very good weed suppressant
Ø Quick to establish
Ø Best sown in the early autumn
Ø 25-35kg / ha
Green Reward
Ø Multi species mixture with different root and growth habits
Ø High biomass yield and root penetration
Ø Good weed suppressant
Ø Contains: Winter Rye, Black Oat, Oilseed Radish, Tillage Radish, Mustard, Vetch & Phacelia
Ø Sow at 45-50kg per ha in August/ September
Commando
Ø Specifically designed for Bio Fumigation
Ø Fast to establish and easy to chop & incorporate
Ø Contains: Oilseed Radish, Kale/Mustard hybrid & Mustard
Ø Sow at 40-50kg per ha in August/September
Red Reviver
Ø Designed to under sow cereal crops
Ø Fast to establish, and will help prevent water run off
Ø Contains: IRG & Crimson Clover
Ø Sow at 20kg / ha
EcoCover
Ø The mustard element will be quick to establish and grow, while the rye fills in the bottom growth, aiming to supress weeds efficiently.
Ø Contains Rye and White Mustard
Ø Sow at 25-50kg / ha
N Fixer
Ø The species in this mix have been chosen to maximise nitrogen fixation in their growing period.
Ø Contains Red Vetch and Berseem Clover
Ø Sow at 15kg / ha
Spring Provider – Westerwolds & Vetch
Hydro Max – White & Brown Mustard
Soil Conditioner – Rye, Buckwheat, Linseed, Oil Radish, Mustard & Phacelia
Autumn DM - 80% Rye, 15% Vetch, 5% Phacelia
Custom mixes are available; please call the seed department to discuss your individual requirements. These custom orders cannot be cancelled or returned due to the specialised nature of the order.
Nutrient uptake
Looking at the data over a three month period, we can see how the nutrient uptake has varied between species and treatment. Broken down into Major or Minor nutrients and Carbon uptake.
Major nutrient uptake
Generally, the Nitrogen in the plant has increased, over the first two months and then dropped back down by the third month.
The Winter Vetch (nacre) has also seen a decrease in Nitrogen, which could be accounted for by the lack of active growth from the cold soils, not utilizing the root nodulation.
Whilst staying the most consistent in Nitrogen uptake, the Soil Improver mix saw a drastic drop in overall major nutrient uptake by January. This is also seen in the Sprinter mix.
Kora Buckwheat has seen the best increase as a single species from the first two months, followed by a drop in uptake which is most likely due to the plant beginning to senesce from the frosts.
The radish Discovery is the species that has seen, even though it is marginal, an increase in nutrient uptake in January. The Romesa radish, similarly, has not seen as much as a decrease as other species or mixes in this month.
Minor nutrient uptake
Uptake on the minor nutrients is commonly increased with the single species in the first two months and decreased in the mixes. The majority of species and mixes have seen a decrease in January uptake. The Soil Improver mix is the only one to stay consistent in the uptake of the minor nutrients.
As the Buckwheat begins senescing the uptake has decreased, show here with the decrease in uptake over the three months.
The Sprinter mix has seen a significant decrease in the uptake of Molybdenum, compared to the other nutrients.
Untreated Carbon
The majority of plots have seen an overall increase in the uptake of carbon, over the three months samples.
The mixtures have a better uptake than the single species, with the N Fixer and Green reward showing the biggest difference between November and December, and an increase in January uptake.
Both types of radishes have seen an increase in the January uptake.
Only the N Fixer and Sprinter mixes have seen an overall increase in carbon uptake.
If you have any queries on cover crops, contact our team today on 01243 755620 or seed@bartholomews.co.uk