Improved soil structure, higher organic matter, suppression of blackgrass, and increased yields. These are some of the benefits to support the introduction of cover crops into the rotation and they make an appealing list to growers.
However, those looking to grow cover crops need to be clear about their own objectives and be realistic about what the crops can really offer, says Strutt & Parker consultant George Badger.
“While there is data there to suggest they have a place in some rotations on some farms, for others they may prove to be a distraction rather than a profitable addition,” he says.
Cover crops tips
- Keep the seed cost as cheap as possible by using “what’s in the shed”
- Have a strategy of what you want to achieve from the crop
- Avoid rotational conflicts with legumes, brassicas and cereals
- Sow straight after harvest for vigorous establishment as gaps in the crop can slump over winter
- Ensure thorough destruction to kill any germinated blackgrass, this could require two sprays
- Focus on establishing a quality spring crop, direct drilling is preferable but cultivation or ploughing may be necessary
Mr Badger adds these crops can be useful in the right conditions, but worries that they are being overhyped.
“There’s a risk that by putting a cover crop in the wrong situation, you can do more damage than good for the following crop and the farm economics as a whole,” he says.
Mr Badger suggests that one of the critical issues is the cost of establishment with some cover crops costing well in excess of £50/ha to grow.
Yet trial results from Niab Tag suggest any yield improvement in winter wheat the following year amounts to just 0.11t/ha on average.
“The data points to yield improvements being minimal, at least in the first few years, so if you look at the cost of the seed then you would say it hasn’t been worth it,” he says.
The data from Niab Tag showing an average 0.11 t/ha yield rise was taken from 2010 and 2012 using a radish cover crop in the preceding spring crop and a standard nitrogen programme.
That equates to a £45/ha seed cost for a £13/ha yield gain in the following wheat, Mr Badger points out.
He admits it is not all about yield, but adds it is very difficult to quantify the results of cover crops because how do you measure their success?
“Is it percentage organic matter increases, nitrogen savings from fixation and catching, quality of following crop establishment or levels of compaction with soil penetrometer?” he asks.
Growers looking for more low-cost cover crops should consider using home-saved cereals and mustards, which can reduce the seed cost to £15/ha.
“Home-saved spring oats are fast to establish and a cheap alternative for growers already with oats in the rotation,” he adds.
A barley and mustard mix is probably the cheapest option for qualifying as an Ecological Focus Area. Where nitrogen fixation is the aim, growers could also consider reducing a costly vetch seed rate and replacing this with home-saved peas or field beans to give the same effect.
Mr Badger explains that growers also need to be careful to avoid any rotational conflicts when choosing a mix.
“It is best to avoid using vetches in rotations containing peas and beans, or at least provide a three-year minimum break to avoid the hosting of fusarium foot rot, sclerotinia and chocolate spot,” he says
Similarly, a brassica containing mix should not be used where oilseed rape is in a tight rotation, he advises.
Claims that cover crops are the answer to dealing with blackgrass problems may also be overstated.
“The data points to yield improvements being minimal, at least in the first few years, so if you look at the cost of the seed then you would say it hasn’t been worth it.”
George Badger, Strutt & Parker
Last year, he experimented by drilling a field with oilseed radish as a cover crop ahead of spring barley. It was a heavy land field with a known blackgrass history.
Despite the deep tap roots of the radish aiding infiltration, it was too wet to direct drill in the spring so the group had to be cultivated.
This meant that all the benefit were lost because seeds from below 5cm were brought up which consequently germinated in the spring barley.
The lesson learned here was that the cover crop cannot replace good field drainage, and they need to be employed on fields that you know will cope with direct drilling in the spring.
There is evidence that some brassica cover crops release isothiocyanates which can suppress blackgrass germination, but for some growers their strategy is to decrease the seed bank and the cover crop merely acts as a trap crop to be sprayed off in the spring.
Therefore, the key cultural control of blackgrass is from spring cropping or delayed drilling, regardless of the mix sown. If blackgrass is the primary concern, ploughing in good conditions and establishing a competitive spring crop may be the safest option.
“There are farms who are making cover crops work for them. But growers just dipping in and trying them for the first year need to be aware they might not see the results for that first year and might even be worse off,” he says.
Mr Badger adds that if cover crops are used for five years you might get a long-term benefit but at the moment there isn’t much independent data to support this.
|Cover crops comparison|
|Cover mix||Seed rate kg/ha||£/kg||£/ha|
|Spring oat (HSS)||30||0.20||41|
|Spring oat (HSS)||30||0.20||29|
|Spring oat (HSS)||20||0.20||16|