As featured in Arable Farming Magazine
Getting black-grass control back on track
by Arable Farming September 2020
Introducing cover crops and extending and diversifying the rotation is delivering rapid and significant soil health benefits on heavy, silty clays at Agrovista’s Project Lamport.
Trials at the Project Lamport site in Northamptonshire have shown that reverting to winter wheat too soon after a period of spring cropping can result in an
explosion of black-grass. When this happens, the standard advice is to press the reset button and plough.
However, Agrovista’s latest research suggests a cover crop/ spring crop sequence is a better choice, explains technical manager Mark Hemmant.
The trial followed a disastrous winter wheat crop with more than 800 black-grass heads/ sq.m. The area was straw-raked and ultra-shallow disced on September 5 then combi-drilled with 15kg/hectare of a black oat and phacelia cover crop mix.
The cover and emerged black-grass was sprayed off with glyphosate on February 5 and again on March 25. Spring oats were direct drilled with a no-till Weaving GD drill at 350 seeds/sq.m on March 27.
The only residual herbicide applied was 100g/ha of diflufenican on April 1.
“We established an excellent crop of spring oats and achieved fantastic black-grass control,” says Mr Hemmant.
“We trapped young plants successfully in the cover crop and minimised soil disturbance when the oats were drilled.”
Cover cropping is also said to have shown outstanding control of black-grass in the spring wheat this summer.
Protecting soil health at cover crop establishment
Ultra-shallow discs have superseded the power harrow as the tool of choice for cover crop seedbeds at Project Lamport. Niall Atkinson, Agrovista arm systems research and development adviser, says:
“When establishing the cover crop the aim was to try to make the black-grass grow in it so we could trap it and destroy it with glyphosate ahead of the spring cereal.
“At the start of the project we used a power harrow to achieve the necessary soil movement. It did a really good job of establishing the cover crop and setting off the black-grass, so we had a really good kill.
“However, it has become evident how much damage power harrowing was doing to soil structure and soil biology.”
A Vaderstad Carrier fitted with CrossCutter discs designed to work at just 2-3cm is now being used.
“This still provides a good black-grass chit, but without the detrimental effect of the deeper rotary cultivation,” says Mr Atkinson.
Straw raking has proved very useful where a light cultivation is not required, spreading crop residues and giving a good chit of volunteers and grassweeds, offering a step up in soil health terms through less soil disturbance, he adds.
However, the cover crop/ spring wheat sequence has been so successful that stimulating a pre-cover blackgrass chit is not always required.
Wet season resilience
The beneficial effect of cover crops stood out during the wet autumn and winter at Project Lamport.
Plots cropped with an overwintered cover crop/ spring wheat sequence allowed water to infiltrate much more readily than those fallowed ahead of the spring wheat.
“We rarely saw any surface water on the covercropped plots even after the heaviest of rain,” says Niall Atkinson.
“There was very little puddling, and what was there disappeared quickly, whereas the fallowed plot suffered badly, despite having been subsoiled in autumn. The soil ran together and fines were washed into the channels, sealing the surface.
“This is a problem we see on high silt soils. You end up having to cultivate it again in front of the spring crop, which destroys any structure that might remain.”
Soils were wet and cold and cover crops on their own didn’t establish as well as usual. “They still did a good job, but where we had identified a need and used the subsoiler as well, we got a better result with the cover crop and a slight improvement in spring wheat establishment.”