Autumn cover crop options
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:
Why?
· Nitrogen fixation
· Reduced leaching
· Improved soil organic matter content, incorporating the green manure
· Better soil structure, using a range of species with different rooting depths can create drainage channels and break through soil pans.
· Weed control, a lot of the species used produce masses of biomass which can supress weeds coming up. Some species also have allelopathic qualities, and
· Reducing soil compaction, through the root mass produced, as well as the deep rooting species.
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. Over 55% of river water bodies and 73% of lake water assessed for P in England failed the revised phosphates standards for good ecological status according to a survey carried out by the Environment Agency in 2019. These statistics highlight the problems caused by agriculture to our local environment, but you can help reduce these pollutants on your farm by planting a cover crop such as our Grabber mix or our Soil Improver 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.
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?
· Most species / mixes can go in from August to September
· 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. Can be used if OSR is in the rotation. Not winter hardy.
Suggested sowing rate – 10-15kg/ha
Sow April - October
EFA Compliant
Vetch
Very suitable for fixing nitrogen, even in a relatively short space of time. It works well as a companion to Rye. Winter hardiness depends on variety but will break down quickly once incorporated. Can offer some effectiveness at weed control with the biomass produced.
Suggested sowing rate – 50kg/ha
Sow March - October
EFA compliant
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 mount of biomass. This makes it excellent at preventing leaving and controlling weeds. Can improve soil structure and build organic matter but it is not winter hardy. Brown mustard is used in situations where a bio-fumigant is needed and is more winter hardy.
Suggested sowing rate – 10-15kg/ha
Sow April - September
EFA compliant
Radish
Broken down into two main types, there is the oil radish and the tillage radish. Both options have large roots, but the tillage radish will produce a significantly larger and longer root than the oil 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. 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.
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
EFA compliant
Rye
A quick growing option that is fantastic for preventing leaving 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.
Suggested sowing rate – 30-50kg/ha
Sow August - October
EFA compliant
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. Can be sensitive to frost but have the ability to be sown up until October.
Suggested sowing rate – 30-50kg/ha
Sow August - October
EFA compliant
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
Why use a mix?
Mixes are a great way to maximise the individual benefits of the species.
Using species with different rooting depths and growth habits to offer the most advantages, improving the soil for future
Suggest mixes
Grabber – 80% Rye, 20% Vetch
Autumn DM - 80% Rye, 15% Vetch, 5% Phacelia
EcoCover - 80% Rye, 20% White Mustard
Sprinter – 80% Black Oats, 30% Vetch
N Fixer – 80% Red Vetch, 20% Berseem Clover
Green Reward – Rye, Oats, Radish, Mustard, Vetch & Phacelia
Soil Improver – Oats, Mustard, Radish & Phacelia
Commando – Oil Radish, Carbon, Mustard
Red Reviver – IRG & Crimson Clover
Spring Provider – Westerwolds & Vetch
Hydro Max – White & Brown Mustard
Soil Conditioner – Rye, Buckwheat, Linseed, Oil Radish, Mustard & Phacelia
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.
At Bartholomews, we can put together a bespoke mix for your needs, please contact the seed department for more information. Call 01243 755620 or email seed@bartholomews.co.uk