Long-term direct driller reveals yield impact of ploughing again

A wheat crop established under the plough yielded 1.7t/ha more than the long-term direct drilled part of the field, more than paying for the extra costs associated with ploughing.

But a similar experiment comparing direct drilled and ploughed linseed on the farm had the opposite result, wiping out any increased profitability.

Essex farmer Simon Cowell set up his plough versus direct drill experiments after seeing wheat yields stagnate on the farm, despite the improved soil structure and biological activity resulting from direct drilling the farm’s predominantly heavy clay soils for more than 20 years.

See also: Why a long-term no-tiller is ploughing again on heavy soils

“I wanted to see whether by ploughing once every six to 10 years I can make a difference and improve yields without unduly impacting those soil improvements,” he says.

After ploughing one-third of the wheat field in dry conditions last September, he set the scene for the perfect comparison of the two establishment techniques.

This included differences in workability with a two-week delay in drilling the ploughed part after it laid too wet to drill after the early October rains.

Wheat field showing ploughed and direct drilled areas © Mike Abram

Soil tests shortly after drilling showed very little difference except for slightly lower organic matter in the ploughed plots.

This, Simon suggests, was down to dilution from deeper clay soil mixed with the higher organic matter that’s been built up over the years of zero-tillage.

In-season tissue tests were also similar, in terms of the percentage of nitrogen and nutrient contents between the two establishment systems.

But satellite Normalized Difference Vegetation Index (NDVI) imagery taken from February to just before harvest in July showed how the crop changed during the spring.

It revealed that the later-drilled ploughed crop initially had clearly lower biomass.

By mid-April that had changed, with biomass relatively similar across the field for both systems, and in June the plough clearly had much greater biomass than the direct-drilled system.

Differences reflected in yields

Those differences appear to have been reflected in the yields, with the ploughed area averaging 8.2t/ha, against 6.5t/ha for the long-term direct-drilled part of the field.

This was measured by a Griffith Elder grain weigher on the combine that weighs every load, Simon says.

“I weigh every tramline on the farm, emptying on the headland after each one and writing down the yield.”

At a wheat price of £160/t, the 1.7t/ha difference was worth an extra £270/ha in favour of the ploughed side, he calculates.

Using standard John Nix Farm Management Pocketbook figures for the cost of ploughing and other cultivations needed to make a seed-bed of £175/ha, it left an extra £95/ha in margin.

“My costs are lower because I’m using old machinery,” he says.

But that benefit was more than wiped out by a similar trial in linseed. In this case, Simon chose two neighbouring fields to compare.

“The direct-drilled field went into perfect conditions – it came up in five days and looked a fantastic crop.”

Second field

The second field was ploughed in better conditions in November, but needed power harrowing in the spring to create a seed-bed. “It was a bit rough, and by power harrowing I lost what little moisture there was.

“Even so, it was in good condition to drill into, but establishment was a bit uneven, and around 20% didn’t emerge until we had a good rain two to three weeks later,” Simon says.

“Once it got going, the ploughed crop grew with much more vigour – it was about five inches taller than the direct drilled, with more biomass.

“It was much thicker and looked like it was going to yield easily more than the direct-drilled field.”

But to his surprise that wasn’t the case with the direct-drilled field achieving 2.5t/ha against 2.1t/ha for the ploughed field. Both were better than the 1.8-2t/ha he would usually expect.

“The ground in the ploughed field, once we had the dry weather, cracked open and dried out, so I don’t think the crop was able to finish properly.

“Any money I gained by ploughing for the wheat was soon lost with the linseed this year.”

As a seed crop, the linseed should sell for around £600/t, meaning a £240/ha advantage for the direct-drilled field, plus the £175/ha ploughing costs, adding up to £415/ha in additional margin.

Looking forward

One year’s results shouldn’t and won’t lead to any drastic change in farm policy, Simon acknowledges.

“It also reaffirms that ploughing isn’t such a reliable way of establishing crops. On this heavy land, direct drilling is brilliant in that you can just go and drill in the right conditions and it comes up perfectly.

“Whereas with ploughing, you’re so much more dependent on weather.

“If it hadn’t rained after I’d ploughed in the dry conditions, I wouldn’t have had a crop as I wouldn’t have been able to make a seed-bed out of the clods of clay.”

Instead, he’s planning a continuation of the trials. “In the wheat field, there are nine tramlines, with three ploughed last year.

I’m going to plough the next three tramlines, so I will then have a comparison between wheat direct drilled in the second year after ploughing, freshly ploughed and drilled, and long term direct drilled.”

In addition, he chopped the straw on the first tramline in each section, which will provide a comparison between baling and chopping.

“I was finding the worms weren’t taking the straw down in long term direct drilled, so I want to see if having reset to some extent, whether that starts working better again,” Simon explains.

He’s also tempted to repeat the experiment in a linseed field. “It did look like a much better crop where I ploughed and just went wrong at the end, so I’m tempted to try again.”

Last year’s linseed fields will be first wheats in the coming season, providing another possible comparative data point.

Measuring and monitoring will be improved in-season after applying for a Defra-funded Adopt grant, which is designed to support farmer-led, on-farm trials.

That is part of a wider look on the farm at why yields have been limited in his long-term direct-drilling system despite improved soil health.

The project also involves Kent grower Andrew Howard and Groundswell host farmer John Cherry and is being co-ordinated by Daniel Kindred from ARC Agronomic Services.

Other trials

As well as further examining the ploughing comparison, the trials will also investigate observations Simon and the other growers have made during their time direct drilling.

That includes Simon noting that some headlands on the farm consistently outperform the middle of some of his fields.

“The most extreme one this year was 12m of headland wheat yielding just over 10t/ha, whereas the rest of the field did 7.5t/ha,” he says.

“It appears the headland might do better because it is more consolidated from more turning and double rolling, so we’re going to do some strips with some light cultivation and extra heavy rolling to try to mimic what the headlands are like across the field,” he says.

The ploughed area destined for spring linseed © Mike Abrams

A second aspect will be to explore the stratification effect in the soil that long term zero tillage can cause. “We’re going to do lots of testing, comparing different layers.”

That will include pH testing after Simon discovered the top 2cm of his soil is much more acidic compared with the usual soil sample depth of 15cm, which tests as neutral.

“Is that making a difference to the availability of nutrients that are concentrated in the top layer?

“We also want to investigate auto-toxic chemicals, which will be concentrated in the top layer of the soil, and I think could be having a detrimental effect.”

In a low rainfall area, they’re not leached away, especially on clay soils, nor mixed into the soil profile in a direct-drill system, he points out.

“A lot of people have asked why I don’t plough to get a higher yield, but if we can discover why it’s different, maybe we can get the yield without ploughing,” he concludes.

Soil profile from direct-drilled wheat © Simon Cowell