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Trials cut through the cover crop hype

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Avoid single species cover crops and tailor mixes to farm conditions and objectives to get the best results out of this much-hyped addition to arable rotations, say organisers of a new field-scale demonstration.

Farmacy’s 60-acre Calcethorpe cover crop demonstration site at Glebe Farm near Louth on the Lincolnshire Wolds is evaluating a range of seed mixes and management techniques to give growers a practical insight into the reality of growing cover crops.

The trials have already shown how selecting the right cover crop mix brings a host of benefits above and below ground and organisers expect to see clear yield benefits from improved soil structure and nutrition in the subsequent spring barley crop.

Alice Cannon

“You don’t have to spend a fortune on exotic mixes, but you do have to select species that will work for your situation,” says Market Rasen-based Farmacy agronomist Alice Cannon.

“It is possible to establish an effective cover crop for £20-40/ha, which is half the cost of some mixes, and maybe lower if you’re able to home-save some seed, however there is a clear purpose to these crops and investing in the correct species is vital.”

There are a number of reasons for sowing a cover crop (see below), but no single species or mix can achieve all of these benefits so growers must prioritise the main aims for specific field conditions, she says.

“Once you’re clear what you want from the cover crop, select a mix that can achieve these results.”
Cover crop benefits:

• Improving soil health by providing food for soil fauna and flora
• Better soil structure and natural aggregation from root and biomass growth
• Adds fertility (nitrogen) and organic matter
• Reduces leaching
• Moisture retention (light soil)
• Prevents erosion (wind and water)
• Suppresses weeds
• Dries soil from depth (heavy land)
• Forage for livestock.

Mixes show more resilience

Miss Cannon urges growers to avoid single species cover crops and choose mixes based on at least three different options.

“The resilience of cover crops to pests and diseases really improves when they’re used in a mix. The presence of other species ‘confuses’ pests, reduces the transfer of diseases and also spreads the risk of crop failure should a problem occur with one species.”

This was clearly highlighted in the Calcethorpe trials this autumn where all single species plots of peas and vetch following vining peas were decimated by pea and bean weevil, whereas only minimal damage was seen in legumes sown as part of a mix. Similarly, oats suffered significantly more BYDV and crown rust where sown alone rather than in a mix.

Mixing species also brings different attributes in terms of root growth and above-ground biomass production, Hutchinsons technical manager Dick Neale adds. Crops such as linseed and sunflower produce large fibrous root systems, while others like radish and mustard put down a larger tap root able to break compaction layers.

“We’ve seen roots go down to at least 1m and in general I’d expect to see 50% more root growth than top growth in most crops, however this depends on the drilling date and establishment conditions.

“Extremely dry conditions have seen some August drillings perform very poorly in 2016 while later sowings into moisture have flown out of the ground. The aim is to get a mix of roots in the ground, but the type of crop sown depends on what you want to achieve.

“The cultivation benefits of cover crops can be significant, but you must be prepared to give them time to work, at least three years ideally.”
Even within crops there is quite a variation in their characteristics and potential benefits, so it is worth seeking advice on the best option for your situation, Miss Cannon says.

White mustard for example is fast to establish and produces more above-ground biomass than brown mustard, but stems have a tendency to turn “woody” post-flowering and nitrogen is less readily available to the following crop.

White mustard may therefore be a better catch crop option where growers want a lot of biomass quickly but are prepared to wait a season for the nutritional release, whereas brown mustard may be preferred for a quick fertility boost in the following crop, she notes.

Heavy versus light land options

The most appropriate cover crop options vary considerably depending on soil type.

On light, drought-prone land, such as Glebe Farm, spring moisture retention within the soil is a major draw of cover crops, Mr Neale says. Mixes should therefore include crops with dense fibrous root systems that bind soil together well and also have “flatter” top growth to cover the soil surface and retain moisture.

Establishing cover crops 2

The favoured mix in these trials is based on 57kg/ha spring oats, with 1kg/ha white mustard, 7kg/ha spring linseed, 38kg/ha spring beans and 33kg/ha spring peas.

“On this land I’d expect an extra 0.5t/ha yield in the following spring barley crop from the extra moisture retention this cover crop delivers,” he notes.

Conversely, on heavy land, especially where black-grass management is an issue, Mr Neale recommends species with deeper roots able to penetrate dense layers and dry soil from depth.

Top growth should be more erect to allow light and air to reach the soil surface to stimulate black-grass germination and let land dry out in spring. Spring oats and linseed are particularly suited to this, he adds.

Destruction timing is key

Desiccation timing is critical to get the best results from cover crops and the optimum will vary for every site, Mr Neale says.
Generally, cover crops on light land can be sprayed off with glyphosate closer to drilling than those on heavy land.

The moisture held in the top growth and roots within the seeding zone is an asset to the new crop on drought-prone land, whereas on heavier soils earlier termination of the cover crop – typically at least six weeks before drilling - allows more time for surface layers to dry out, he explains.

Again species mix is key in relation to the “exit” strategy. Oats or rye must be sprayed or grazed off at least five weeks ahead of a following spring cereal, regardless of soil type, because they produce negative allelopathy and will cause a delay in growth.

If top growth is to be retained, ask whether your drill can handle it? These issues should be planned for as you do not want to delay spring sowing of cereals or yield will be lost due to a lack of tillering time.

Growers are reminded that EFA legislation requires eligible catch crop mixes to be established by 31 August and retained until at least 1 October, while cover crops must be established by 1 October and retained until 15 January.

Find out more

Two more free demonstration days are due to be held at the Calcethorpe cover crop site next year.

In February there will be an event showcasing different termination methods for cover crops, while a separate drill demonstration day in March will examine how different drills cope with drilling into cover crops.

Contact Alice Cannon ([email protected] – 07583 692576) for more information and to register your interest in attending.

Tips for getting the most from cover crops:

• Be clear of the reasons for using a cover crop
• Avoid single species mixes – minimum of three different species
• Tailor mixes to end goal and farm characteristics
• Exotic and expensive mixes are not always best
• Reduce costs by home-saving seed
• Establish cover correctly – treat it like a crop
• Time desiccation correctly according to soil type and following crop.