For more than 20 years, a bare brown field has not been seen on Motts Farm on the Dengie peninsula in Essex, with crops established using zero tillage.

But that changed last autumn. Two fields were ploughed on Simon Cowell’s farm as an experiment.

He wanted to see whether yields can be improved without unduly impacting soil structure and biological improvements built up over the long period of zero soil movement.

See also: Soils improve for Northants grower after a switch to regen

No-till was adopted on the farm’s predominantly heavy clay soils in the 1990s because of the challenges in establishing crops, Simon explains:

“It was getting more and more difficult to work soils to get a seed-bed using cultivation.”

Switching to no-till was a revolution, transforming soil structure, improving trafficability, increasing biological activity and lowering input costs.

It also allowed him to bring spring crops back into the rotation.

Stagnating yields

Wheat yields have stagnated to some extent over the years, not reaching the highs of 11t/ha that he recalls from before he switched to direct drilling.

Spring linseed yields of 2.5t/ha are also a thing of the past.

That’s one of the reasons that’s led him to plough one whole field and part of another with a second-hand Kverneland manual vari-width plough.

He cut down the furrows to 27.5cm (11in) to ensure ploughing is as shallow as possible.

“I want to see whether by ploughing once every six to 10 years I can make a difference and improve yields.”

But it’s far from the only reason, which is also based on observations on the farm.

An old dairy farm, he still has areas that have been permanent pasture since land was reclaimed from the sea roughly 300 years ago.

In that time, only about 10cm of topsoil has built up, he points out.

“I’ve always thought we could keep sequestering carbon and building organic matter and that layer would keep getting deeper and deeper. But looking at this, it does seem there is a natural limit.

“And in my arable fields I’ve already achieved that after 20 years,” he says. “The scientists say you reach carbon saturation and I think that’s what I’ve reached.”

In the 20-plus years since switching to no-till, soil organic matters have increased from 3.5% to roughly 8%, a result also helped by other practices including applications of compost.

Worm concerns

“Another thing that started to concern me was the earthworms weren’t taking straw down anymore.

“When I started direct drilling, chopped straw disappeared in about eight weeks. In the past five years they seem to have lost all interest in it.

“I think that’s because the soil doesn’t need any more carbon, and the worms have enough to live on by cycling what’s in the soil already.”

This led to his theory that he needs to turn the soil over to restart the process, and in doing so should also mineralise some nitrogen and other nutrients.

“When you’re direct drilling, you’re immobilising nutrients to some degree if you’re building organic matter.

“There’s a 10:1 carbon-to-nitrogen ratio in organic matter, which means for every tonne of carbon you put down, there’s 100kg of nitrogen you are tying up in the organic matter – it’s the same for other nutrients tied up in organic matter.

“And while the theory is you should get more nutrient cycling when the soil biology is working, it’s not going to be as much if you’re also building organic matter, as it is tying up more than it is releasing – otherwise it wouldn’t be building.”

If that holds true, building organic matter has a nutrient cost, he suggests. “So I keep coming back to the idea there’s no point in building organic matter if you’re not going to use it.

“And the only way is to release it out of the organic matter, to mineralise it, which is what we may or may not see by ploughing.”

First field

Perhaps fortunately, as it turns out, when ploughing his first field in mid-September, conditions were a little too dry.

He found he wasn’t making as good a job of turning over soil as he wanted, especially for burying grassweeds.

“So I stopped and it means I’ve got a great experiment where I can compare wheat established following ploughing with no-till in the same field.”

First comparisons will be made via soil test to see whether the plough has mineralised organic matter.

He will attempt to quantify how much carbon has been lost through a single ploughing operation.

Yields will also be compared in wheat this year, where the ploughed land could only be planted two weeks after the direct-drilled crop.

“When it came wet in October, the ploughed land held the water and was too wet to drill,” Simon explains.

“The direct-drilled part of the field was drier on top and drilled beautifully.”

Second field

The second field intended for spring linseed was ploughed in November, with a neighbouring field being used to compare. “That ploughed nicely,” he says.

Ploughing now compared with 20 years ago is completely different, he adds. “The soil is a different colour, darker black, and it was easy to make a seed-bed – it crumbles nicely.”

He’s hoping that mixing deeper clay soil with the 10cm of higher organic matter topsoil might also help reduce the impact of stratification.

“A potential problem with direct drilling is concentrating everything on top, so all the biological activity is at the surface.

“When you get a dry summer, the biology shuts down and the crops are left high and dry for nutrients.

“If you have a mixed soil, there is less risk of stratification, and there is more chance of biological activity to a deeper depth, as long as it is aerobic.”

Grassweed benefit

Another potential benefit of ploughing is for grassweed control. Blackgrass remains an issue on the farm, while there is also some Italian ryegrass.

“The theory is by keeping the weed seed on the surface, the pre-emergence sprays work better because it’s near the seed, and obviously you’re not mixing seed down to depth.

“But while grassweed problems haven’t got any worse and I don’t think they impact yield, we still need to be at the top end of herbicide spend.

“So hopefully one-off ploughing should make a big difference and reduce numbers.”

His last reason for ploughing is more theoretical, after reading a book by Russian soil microbiologist Nikolai Krasilnikov.

It discusses the potential negative impacts on crop growth from toxic chemicals produced by crops and microbes.

“The obvious example of autotoxicity is lucerne. It’s well known you cannot get a lucerne seed to germinate in a stand of lucerne.

“But there are loads of other examples – it’s not just root exudates but also bacteria associated with a crop that will prevent other plants growing.

“It seems these chemicals are pretty persistent, particularly in clay soils, and I’m wondering whether in a direct-drilling situation they’re hanging around and reducing yields.

“Krasilnikov suggests ploughed soils have lower amounts of these toxic substances.”

Declining break crop yields

He cites the decline in yields from some break crops, such as peas, on the farm to the extent that he no longer grows them as possible anecdotal evidence of this phenomenon.

Therefore he does not think that it’s all a result of soil-borne diseases.

“That might allow me to grow these crops again and widen my rotation.

“But obviously I won’t know, if I have success, whether it’s because I’ve disrupted these chemicals or it’s because I’ve mineralised some nutrients,” he admits.

Ultimately, yield and cost will drive whether ploughing becomes a slightly more regular site across the farm, he stresses.  

“I haven’t worked out yet what type of yield response I would need to justify ploughing, but I think if went from 8.75t/ha to 10t/ha, that would cover a lot of work.”