Article taken from Agronomist & Arable Farmer, August 2017, written by John Swire.
For the fourth season running at Agrovista's Project Lamport site in Northamptonshire, where untreated resistant blackgrass plants exceed 2,000/sqm, the best black-grass control has been achieved using a black oat-based cover crop, in tandem with direct-drilled spring wheat.
This cover crop is initially slow to grow. Combined with the light discing and combi-drilling used to establish the cover crop in early autumn, it maximises black-grass germination and establishment. The black oats then bulk up to condition and drain heavy soils over winter, before being burnt off, along with the black-grass, ahead of the spring wheat.
A profitable spring wheat crop has been established on the potentially difficult clay soils at Lamport over a series of very different seasons using this system, says Agrovista technical manager Stewart Woodhead. At the same time, it has driven down blackgrass numbers in crops and reduced the soil seed bank.
""It is well documented that spring drilling is key to controlling grass weeds. The challenge is to spring drill consistently well," said Mr Woodhead. ""The key is to move the soil to maximise black-grass germination when we establish the cover crop so we 'capture' it and kill as much as possible when the cover crop is burnt off.
""We than want to minimise soil movement when establishing the wheat crop to minimise the chances of a spring flush. The last thing we want to do is select for spring germination - we are effectively limited to an annual meadow grass type of spray programme in spring cereals, so most of the effect is coming from cultural control.""
The spring wheat, KWS Willow, was sown at 500 seeds/ sqm on March 28 with a Great Plains Saxon direct drill. other drill types, such as a Vaderstad drill with its legs removed, can produce a similar low disturbance performance, said Mr Woodhead.
Seed rate is key, while careful attention must be paid at all times. He added: ""We only expect 40-60% germination in this land and crop competition is important - black-grass will quickly fill any gaps.
""You need to check tractor tyre pressure and travel at the appropriate speed and direction to reduce unnecessary soil movement.""
Last year, spring wheat achieved almost St/ha under this system, producing profits of more than £900/ha. The black-grass count was just 8.4 heads/ha.
By contrast, the standard farm practice plot (two winter wheats followed by oilseed rape) of first wheat, combidrilled at the end of September, is inundated with black- grass, despite a full herbicide programme costing around £150/ha over the past four years.
""The plot still contains about 500 heads/sqm," said Mr Woodhead. ""We are expecting this wheat to yield around 5-7t/ ha, which will lose money.""
No quick fix
Reverting to a winter cropping regime too soon can quickly undo all the good work, Mr Woodhead warned.
In autumn 2015, one plot was put back into winter wheat after two years of overwintered cover crop/spring wheat. ""This was a massive mistake - we got an enormous chit of blackgrass," he said.
The cover crop/spring wheat sequence was reintroduced this season but has had to be sprayed off due to the blackgrass pressure.
""We played our trump card with the plough when we established Project Lamport in 2012," he said.
""Back then, only about 40% control was being achieved with a full herbicide programme. Even after four seasons there will still be plenty of viable black-grass seed below the surface, so we certainly don't want to plough that up again.
""It can take a number of years to reduce this seed bank to manageable levels, even without returning black-grass seed to the soil, which means several seasons of at least 98% control.""
The project's aim
Project Lamport consists of 14 rotational systems set within a high population of resistant black-grass.
The project incorporates winter and spring cropping and a range of new initiatives, including the latest cover crops. These are being compared with a traditional winter wheat and OSR rotation, latedrilled winter wheat and spring wheat against a backdrop of heavy land.
The success of each rotation will be based on final black-grass control, economic return and the nutritional and soil-conditioning benefits of cover crops.