‘Appropriate’ tillage is still good for farming

Fewer cultivations can be good for soil structure and health – but ploughing still has its place and can bring dividends, suggests the latest research.

Nitrogen Use Efficiency (NUE) and greenhouse gas emissions both depend on crop productivity. And despite the ups and downs of grain markets and input costs, yield remains the driver of arable profitability.

This means tillage in itself need not be bad for the environment, according to field-scale trials undertaken by Agrii at the agronomy company’s long-established grassweed management technology centre at Stow Longa, near Huntingdon.

Agrii agronomy specialist Colin Lloyd has overseen more than two decades of research-led at Stow Longa. And he sees plenty of room for “appropriate” tillage in arable rotations on heavy land in particular.

“You can analyse your performance down to the last square metre of land or litre of diesel. But whatever you do, you can’t get away from the fact that decent margins have always and will always depend on sufficient yield.

Different rotations

“Yes, grain quality is important – as is effective input and overhead control. But without the tonnes you’re not in the game. Which is exactly what our rotational work with a range of cereals crops is also showing with Nitrogen Use Efficiency (NUE) and carbon emissions.”

For seven years, Mr Lloyd and his research team have managed different rotations in one hectare blocks at Stow Longa. Tillage regimes range from continuous and rotational ploughing to deep one-pass, minimum tillage and direct drilling with catch or cover crops.

As well as huge differences in grassweed populations between different rotations and tillage regimes, their pioneering work has highlighted large differences in margins after cultivations, drilling and all inputs.

In 2022, the range in margins between the best and worst rotation and tillage combination was a £1821/ha. More recently, researchers have extended their work to measure the NUE and greenhouse gas emissions from cereal crops to established protocols.

Heavy clay

Yields of first wheat Fitzroy on heavy clay land in 2022 varied by almost 3.1t/ha between the different tillage regimes. Both continuous ploughing for six years and a plough reset after five years of direct drilling delivered over 9.75t/ha.

In contrast, direct drilling after five years of ploughing and six years of continuous min tilling or direct drilling produced less than 7.25t/ha.

Unsurprisingly, given exactly the same starting soil nitrogen levels and fertiliser applications, this performance was reflected in an NUE of over 67.5% for the higher tillage regimes and under 50% for the lower ones.

“Using the YEN Zero carbon tool, the lowest tillage regimes generated CO2 emissions  some 10% lower per hectare than a ploughed regime. But on a per tonne basis, much higher yields meant emissions from ploughing were 25% lower.

Measuring emissions

“Even the highest emission regimes were well below the current 340kg CO 2eq /tonne UK feed wheat benchmark established by the authoritative 2022 CHAP Net Zero report, with the ploughed areas close to the lowest reported national crop emissions intensity.

“What’s more, we saw the same thing in our Skyway spring barley,” adds Mr Lloyd. “The higher tillage regimes gave NUEs a good 40 percentage points up on the lower tillage ones and per tonne CO2e emissions almost 25% lower.

“Again, it’s all about yield. The plough regimes both produced more than 8.75t/ha against some 6.3t/ha for minimum tillage and direct drill regimes.”

Grassweed populations clearly played their part in these yield differences. But, even after five years of continuous min-tilling or direct drilling with catch and cover crops, our heavy ground can’t support the sort of winter wheat and spring barley yields it is does under the plough.

Work with the UK Centre for Ecology and Hydrology suggests reduced tillage is good for soil microbial populations. But Mr Lloyd says: “We have struggled to see any consistent differences between the regimes in either organic matter levels or soil health scores.”

It has been a slightly different story with the SY Armadillo hybrid winter barley crop. Trrials in 2022 showed much less of a yield difference between the tillage regimes, and similarly smaller NUE and GHG emissions differences.

Encouraging results

After many years of observing how much less affected hybrid barleys are by seedbed conditions than wheat or spring barley, Mr Lloyd attributes this to their ability to cope better with the more challenging conditions the least tillage regimes present on heavy ground.

Overall, he considers the NUE and emission results particularly encouraging for growers with soils less suited to major tillage reductions, pointing out that what clearly counts in environmental terms as much as in economic ones is growing a good crop.

“It’s crystal clear from our work that, however you do it, growing a good crop will reward you in NUE and GHG emissions per tonne of production as well as on the bottom line,” says Mr Lloyd. “And in many situations this may need a decent amount of tillage.

“Appropriate tillage has to be your driver. And recognising the obvious machinery and labour-saving opportunities from tillage reductions, this must mean the least tillage necessary for your particular conditions.

“You shouldn’t shy away from low disturbance lifting of heavy or high silt soils that have become too tight. Nor from using the plough as a reset where grassweed populations have become too high.

“We have to recognise that cultivations aren’t going to completely deplete soils and there is room for them in many rotations, even where the emphasis is on tillage reductions. As with so many other inputs, the secret to success is knowing how much to apply, when and where.”