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Trials show the way on blackgrass control


Article taken from CPM Cover Crops Supplement, April 2018, written by Melanie Jenkins.


Mention cover crops and blackgrass at a farm meeting and you'll probably get a number of opinions on what they do, how well they work and if there's any merit to them at all. Project Lamport, run by Agrovista and partly funded by Bayer, is attempting to put these questions to bed once and for all. Targeted at exploring means of reducing the blackgrass seedbank, the trials have found that spring cropping following specific cover crop species can produce 99% control on blackgrass populations.

Now in its fifth year, the Northants-based project has been extended and is open-ended due to the steep learning curves it's flagged up. However, even now it's proven that blackgrass can be effectively tackled while still making a profit - something that's particularly relevant as so many spring cropping options have become untenable due to the blackgrass burden.

What is particularly significant is the project's consistency, says Mark Hemmant, Agrovista's technical manager. "Continuous years of planting a cover crop followed by a spring crop will result in a visible difference year-on-year in the soil - both in soil drainage and in soil structure. So ideally in the end you get a soil that blackgrass won't want to live in.

"It's about understanding the principles of controlling blackgrass in the long-term, so farmers can drill on heavy land in spring with a reduced blackgrass burden and will able to do so profitably."

Overcome perceptions

The project has had to overcome perceptions about whether cover crops help with blackgrass control at all. "The problem with anything new is that people will try it once and if it doesn't work the first time, then they go back to what they know," says Mark. "They'll happily spend £150 plus on winter wheat herbicide but will only give cover crops a go once."

There's also the issue that those who aren't in a bad situation yet think that change isn't required, can get into trouble quickly, he warns.

Part of achieving consistency in tackling blackgrass has been in selecting the right cover crop for the job.

Lamport has predominantly used a combination of Avena strigosa black oats and common vetch or Berseem clover, but the project has also looked at other crops.

"We've chosen very specific varieties for scientific reasons," explains Mark. "The clover will be killed off with the first frost, the vetch adds different rooting structure to the soil and the black oats won't set seed."

Over four years of running the project, over 98% blackgrass control has been achieved in spring wheat after cover crops, compared with common practice (see table below). The first two years' yields were similar but the low level of blackgrass control in the stale seedbed followed by spring wheat took its toll with the yield dramatically reducing from blackgrass competition.

Companion planting of Berseem clover with oilseed rape works along the same principles as a cover crop but it can be drilled with and matching the OSR rates, says Mark. "This helps to overcome the issue of OSR being a lazy rooter as the clover breaks through the soil and the OSR roots follow it down. It gives better and more even establishment and we've seen up to a 1Vha yield benefit on heavy land and up to 0.251/ha on light land."

Putting a catch crop in followed by late-drilled winter wheat has also proven effective. "We put a catch crop in at the end of Aug, which trapped nutrients and moisture as well as helping to reduce blackgrass, as it was caught when the crop was destroyed. We then drilled the wheat at the back end of Oct," explains Mark. "We were still able to get on the heavy land and have a decent seed bed as the soi I prep had been done when the catch crop was drilled."

Species were selected based on their open spatial patterning to not out-compete blackgrass, but which would pick up biomass later for moisture abstraction.

"The whole point is to get blackgrass to germinate."

Semi-permanent cropping is another area Lamport is looking into with clover. "We had trialled clover as a single cut for a few years in mixes. But a multi cut clover as a semi-permanent crop should aid soil structure."

Getting the right cover crop is just the start, as a fully integrated approach covering a number of other elements, such as seed rate, need to be calculated. A common practice with cover crops has been to drill at high seed rates to smother the blackgrass - something Lamport found to be less effective. "Too much cover crop shadows out the blackgrass, but it'll come back next year in the spring crop," says Mark. "We want the blackgrass to germinate in the autumn so we can burn it off with glyphosate. A lower biomass in the autumn will actively encourage blackgrass to germinate then, rather than in the spring."

The trials have also looked at direct drilling the cover crop after the initial two or three years of moving the soil to stimulate blackgrass germination. "Once you have a reduced burden you can direct drill the cover crop and the spring crop and potentially not move the soil again," he explains.

There's also the question of the drill to be considered. "Working with a number of drill manufacturers we're trying to get the right set up for the drills to fit the system."

Speed and direction of travel have also proven to significantly affect soil disturbance. "We did some work moving at a 90° angle to the planting of the cover crop and found that a lot more soil was being moved, which stimulated the blackgrass."

Increasing speed also saw greater soil disturbance from the drill. "Just by going quickly, you could undo all the good work you've done," warns Mark.

The key is to move the soil when planting the cover crop to get the blackgrass up out of the soil in the autumn. Then, when the spring crop is planted, there should be as little disturbance as possible.

Common practice

Though it should be common practice to adjust tyre pressures when going from a road to your field, this isn't always the case. But findings at Lamport suggest this can make an enormous difference to soil disturbance and subsequently blackgrass germination."We had one field that was very wet in one corner and you could see that the tyres had made a seedbed for blackgrass," says Mark. "Another example saw a tractor come into the field straight from the road and there was a 20m strip of noticeable blackgrass growth where the tyres had kicked up the soil."

Some of the latest research carried out by the project has been to look at earlier desiccation of cover crops. Early desiccation of the cover crop helped to release trapped nutrients from the cover crop more rapidly (see table below). "However, this doesn't mean you can always get in earlier to direct drill the spring crop," warns Mark. "Early desiccation shouldn't be attempted for the first couple of years as growers will first want to get on top of the blackgrass population in the soil surface."

Desiccating too early and not doing a second spray could also mean taking out the cover crop but not small blackgrass beneath the cover crop canopy. "Make sure to get that second spray in."

With greater pressures on chemical usage, there's a move towards a more integrated approach, says Mark.

"We need to be doing everything we can first, before relying on a can."

One trial saw a cover crop planted, followed by spring wheat with no herbicide used. "There was still a reduction in blackgrass, but not as much as there was with chemistry being applied - so there's a need for this integrated approach."

The key learning point from the project has been that attention to detail is vital - but get it right and the results speak for themselves. Agrovista's system has seen spring wheat following a cover crop return 40.67kg/ha of viable blackgrass seed - a massive reduction on spring wheat following a stale seed bed, which had a viable seed return of 236.S?kg/ha.

"It's a game changer in blackgrass control."

However, after three years of this practice, reverting back to previous practice could undo any progress, warns Mark. "Despite some abysmal springs in the past four years, where it's been hard to get crops in, we've still managed to keep the yield up and keep control of blackgrass with this system. This is the future: It just needs patience and the dedication to do it."




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