Rotational ploughing and maximising autumn flushes are part of the new strategy at Tusmore estate near Bicester, as its farm manager looks to get blackgrass back under control.

The grassweed problem that manager Tim Hall inherited when taking on the role was due to a combination of a change to the drill system, extreme seasons and cropping changes resulting from a declining oilseed rape area.

See also: New advice to maximise brome control in cereals

As the estate agronomist, Agrii’s Jamie Lyttle explains that they were walking some spring bean crops a couple of years ago and were concerned about the level of blackgrass germination taking place.

They were particularly interested on why this was occurring after the adoption of a new drill.

Jamie Lyttle (left) and Tim Hall © Proterra

Drilling consequences

A strip-till drill had been introduced as it was the most suited to the farm’s very variable soil types, with stoney brash unsuited for disc drills.

The farm opted for the lower soil disturbance Ipass Mzuri and it has brought many benefits with improvements in soil health.

Tim points out that it has proved effective for establishing both cover crops and spring crops.

However, this change coincided with the introduction of less competitive crops in the rotation with fewer chemistry options. 

The oilseed rape area had shrunk and with a rotation already with significant spring cropping in the form of maize and spring barley, the estate opted for winter breaks with oats and linseed introduced.

On top of these less competitive crops, the dry autumn of 2022 meant they didn’t achieve a good flush of blackgrass ahead of drilling.

So when the drill disturbed the soil ahead of the pre-emergence herbicides, it encouraged blackgrass emergence, Jamie explains.

Agrii area business manager Greg Taylor adds that there was clearly an underlying high level of blackgrass.

“But the reliance on chemistry was too high and there needed to be a cultural element in there.”

Therefore, Jamie set up an on-farm trial, which is about to see its second harvest.

The aim is to investigate ways of tweaking the system and bringing the grassweed back under control.

Maximising flushes

In year one, they looked at cultivations ahead of a direct drill to determine what would encourage the best flush in a stale seed-bed.

The options tested were the Vaderstad TopDown (intensive tine and disc cultivator), Vaderstad Carrier (disc cultivator), low disturbance subsoiler, plough and press and plough and power harrow.

There was also an untreated area where the drill was working on untreated ground – effectively running as it was designed to do.

Blackgrass counts were carried out on the plots two weeks later.

Ploughing effectively buried the seed and virtually none were found.

The TopDown saw 314 plants/sq m, which is about half the number seen with the farm system (658/sq m).

The Carrier was lower, at 115 plants/sq m, while the low disturbance subsoiler was the least successful at 23 plants/sq m. The direct drill was in between at 46/sq m.

“So after the TopDown, you are spraying off half the population that you would see when drilling with the farm standard,” says Jamie.

Drill timing

In year two, the trial was expanded and included three different drill timings – 15 September, 15 November and 22 November.

“We couldn’t drill in October due to the weather, so ended up with two November dates.”

Seed rates were adjusted accordingly at 375, 450 and 525 seeds/sq m for the early, middle and latest dates, respectively.

One clear result was that with later drilling, blackgrass levels fall drastically.

Looking at the untreated area, there were 1,900 plants with the September drilling, 700/sq m with the 15 November timing, and just going a week later (22 November), it was 178 plants/sq m.

“One week made a big difference,” says Jamie.

Ploughing has greatly reduced blackgrass numbers when drilling early (15 September) as shown by the less marked untreated strip (above) compared with the untreated strip on the unploughed area (below) © MAG/Richard Allison

© MAG/Richard Allison

Ploughing reset

Ploughing saw virtually no blackgrass and this clear result has prompted the estate to plough again.

The estate has not ploughed for seven or eight years and this year, 500 acres – about one-third of arable cropping – has been ploughed.

Jamie explains some of this is in front of second wheats and another block was ploughed this spring.

Looking forward, Tim says they are looking at five-year rotational ploughing and using the strip-till drill after.

This seems to be pretty effective and seeing much less blackgrass.

The rotation had already been tweaked to remove the uncompetitive winter oats and linseed and now consists of winter wheat, a second cereal (spring barley or spring wheat) followed by a break crop (beans, spring oats or oilseed rape) and maize.

And finally if there is a danger of high seed return, Tim will wholecrop fields.

Tim explains that there is a local market with neighbouring dairy and cattle farms willing to buy wholecrop forage.