Article taken from Farmers Guide magazine
Written by Dominic Kilburn
Cover crops are proving to be a useful component in the heavy land battle against resistant black-grass, particularly when grown ahead of direct drilled spring wheat and spring barley. Dominic Kilburn explains.
Trials work carried out by Agrovista over the past three years has demonstrated notable improvements in the control of black-grass where cover crops are introduced into the rotation to ""encourage"" the growth of black-grass. Agrovista technical manager, Mark Hemmant is probably being a little kind when he says that growers are in a ""bit of a muddle"" when it comes to black-grass. Speaking at the company's Project Lamport heavy land black-grass trial site near Maidwell in Northamptonshire, he said that despite the fact that growers were struggling to obtain sufficient control of black-grass, they did at least realise that strategies towards its control were going to have to change. ""This site was in continuous wheat and rape for 10 years and if growers in a similar situation carried on like this, they'd just be growing grass, said Mr Hemmant. ""We have to find ways to help them keep farming," he stressed.
Poor control
When the trials began three years ago, black-grass counts on the site numbered 2,000 heads/m2 and a full, robust herbicide programme resulted in only 50 per cent control. ""The reality is that you need 98 per cent control of black-grass just to stand still," he emphasised. ""In this type of area with heavy clay soils, growers have to finish sowing their wheat by mid-October otherwise all the crops don't get drilled, and so delaying drilling isn't really an option. Ploughing can help black-grass control, but not every year otherwise it brings the buried seeds back up again. ""Direct drilling, which offers minimal soil disturbance, should be considered by growers to help reduce black-grass establishing in the crop," he added.
""It's vital that growers pay attention to detail in everything they do establishing their crops in the battle against black-grass, whether that be the use of cover crops, seedrates, direct drilling, tyre pressures to reduce compaction, or herbicide timings and choice. Realistically though, with a big black-grass germination peak in the autumn and the spring, you have to use spring crops if you want to make a difference," he added. While the understanding of cover crops and the benefits they can bring to the rotation is still in its infancy, Mr Hemmant said that the aim at Project Lamport was to investigate those that would have the potential to dry out the soil sufficiently to allow establishment of a spring crop on heavy land by direct drilling, as well as those that' encourage' black-grass to grow at the same time.
""Classic cover crops are put in the ground and cover the soil quickly as they establish, but we wanted a cover crop that would be open enough to allow black-grass to come through and grow with the cover crop before both being sprayed off in the spring. Black oats was an obvious choice as it is renowned for growing in colder conditions and is sufficiently open early on, while still having lots of biomass above and below ground," he explained. ""We tried it here, sowing the cover crop in the autumn following wheat and spraying it off in the spring with glyphosate. It died off nicely and exposed the black-grass below which, in turn, was sprayed off prior to drilling spring barley. ""It gave us some good black-grass control," he added. In plot comparisons this season, similar positive control results are being seen with September drilled cover crops of black oats and vetch ahead of direct drilled spring wheat.
""We have seen in excess of 99 per cent contol of black-grass using these cultural controls only - producing a similar performance to plots where herbicides were also included in the autumn," said Mr Hemmant. ""Farmers on heavier soils don't like the thought of spring crops and drilling spring wheat by direct drill but, although the crops can look scruffy in the spring, they look good by the summer.
""It's a mindset change - about trying to get black-grass growing outside of the cash crop when we can. Many farmers don't want the additional cost of cover crop seed at £30-f40/ha but the alternative is a f 180/ha herbicide cost and still no guarantee of black-grass control;' he said. Mr Hemmant advised that in the first few years of direct drilling spring wheat it's important to create some tilth to help with establishment and use seed rates of 500 seeds/m2 or more. Using less seed, spring wheat doesn't tiller so well allowing more space for black-grass to fill, he said. ""The important lesson is that you must drill the crop parallel to the wheelings of the cover crop for minimal soil disturbance. That said, a crop that establishes well and fills the ground quickly has less black-grass in it even when a field has had more soil disturbance
Spring barley
Results this season also point to good control of black-grass where autumn sown cover crops are grown ahead of spring barley (following winter wheat). KWS Irina was driled at 450 seeds/m2 in early April following the destruction of the cover crop. ""Some growers think that you can't grow spring barley on heavy soils but we think you can," continued Mr Hemmant. ""The seed rate was a little higher than normal, because of the black-grass, and while spring barley doesn't give you quite the same price, it does give you a more flexible sowing date and comes to harvest earlier than spring wheat. ""A first wheat followed by a cover crop and then spring barley makes for a nice entry for oilseed rape," he added.
The late autumn/early winter ahead of drilling spring wheat, rather than waiting until the spring, with the potential benefit of returning nutrients to the soil in readiness for the spring sown crop. ""Cover crops are good at capturing nutrients and we suspect that where they are burnt off early, this has mineralised some of the nutrients and returned them to the soil ready for the spring wheat.
""Cover crops don't grow much more beyond December or January, and they've done what they needed to do by then, so why not spray them off early?"" questioned Mr Hemmant. With all spring sown plots at the trial site receiving 90kg/ha N applied in the row' with the direct drill, Mr Hemmant said that it's important for a spring crop to have readily available nitrogen. ""I think that growers miss a trick when they don't do this, however, we're still learning about the affects of nitrogen in terms of where we put it and when we apply it in relation to black-grass.""
Hybrid rye
While growing hybrid rye for use in an AD plant isn't an option for all growers, trials at Maidwell have shown that when drilled at relatively low seed rates (250 seeds/m2) in the winter, hybrid rye can out-compete black-grass in the spring, resulting in lower counts of black-grass underneath the following OSR crop. ""Rye can be useful for controlling black-grass and gives a reasonable yield. Then, after harvest, which is usually early July when supplying an AD plant, it leaves several weeks of stale seedbed opportunities before the next crop. Beware of low seed rates on heavy soils, however, and the threat of slugs. As a small seeded crop, it mustn't be drilled too deep, advised Mr Hemmant.
Don't do nothing
Despite encouraging levels of black-grass control being seen at Project Lamport to date, particularly where cover crops are grown in the rotation with direct drilled spring sown cereals, Mr Hemmant warned that the worst thing is to assume you are on top of the situation and then do nothing.""Growers must be aware of what black-grass seed remains in the seedbed. Where a plot was left fallow following oilseed rape and then ploughed ahead of spring wheat, we have seen the immediate return of unmanageable levels of black-grass. ""We have found that two years of cover crops and direct drilled spring cereals is not enough, and a return to conventional cultivations and drilling in the third year, without a cover crop, meant that we were in a mess again. ""Black-grass is a numbers game and it's very good at filling space. Carrying on as normal with a wheat/ rape/wheat/rape rotation is not an option," concluded Mr Hemmant