Scottish arable growers should view tillage as another tool in the establishment toolbox rather than something to be avoided in the pursuit of soil health, according to SAC Consulting principal consultant David Ross.
David says the key is not whether farmers cultivate, but whether they use the right system for the individual field and conditions.
“Tillage covers many variants,” he said, ranging from inversion with a plough through to non-inversion cultivation, subsoiling, low-disturbance and shallow cultivation, as well as strip till and direct drilling.
Each system has a different role, and David believes growers need to consider the conditions, crop and problems within an individual field before deciding how much cultivation is required.
When used appropriately, tillage can provide a number of agronomic benefits.
It can bury weeds and weed seed, while reducing the risk of disease carrying over from one crop to another through what is known as the ‘green bridge’.
Cultivation can also incorporate organic manures and chopped straw into the soil profile, while helping to create good seed-to-soil contact for the following crop.
Tillage can encourage nitrogen mineralisation in the soil, potentially supporting crop establishment, and can also help address compaction in the right circumstances.
However, he stresses that cultivation itself can cause compaction if carried out in unsuitable conditions.
Different crops, different approaches
The choice of cultivation system can be particularly important for certain crops.
For winter barley, David says ploughing can help produce a good seedbed required for establishment, while also offering a weed-control benefit where herbicide options are limited.
“It is useful and there are also limited herbicide options for winter barley, so ploughing gives a cleaner start compared to non-inversion,” he said.
Ploughing can also help control volunteer cereals, which can be particularly important where there are limited herbicide options for removing one cereal crop from another.
Spring barley can also benefit from some cultivation before drilling, even where a direct drill is being used.
Inversion tillage can have a role in tackling weeds such as bromes, which can be difficult to control in some crops because of limited herbicide options.
For oilseed rape, meanwhile, reduced tillage can offer advantages because the crop’s long taproot can make use of a greater depth of the soil profile.
Retaining stubble on the surface can also help hide establishing oilseed rape from pests such as pigeons until the crop is established.
Digging deeper on compaction
Compaction is another area where David says farmers need to diagnose the problem before reaching for the cultivator.
“Compaction can be addressed, but this depends very much on where it is found in the soil profile, so you need to get the spade out and see,” he said.
Where deep compaction is found below plough depth, a subsoiler can potentially remedy the problem, provided soil conditions are sufficiently dry to achieve the required shattering through the soil profile.
Where compaction is closer to the surface, low-disturbance legs can be used where less soil movement is required.
Subsoiling can also help water move through the soil profile more effectively when compaction is restricting drainage.
Ploughing can have a role beyond seedbed preparation, too. Following potatoes, David says it can help redistribute windrows of stones and mix them with the finer tilth.
Soil health versus cultivation
The growing focus on soil health can sometimes leave growers reluctant to cultivate, but David says avoiding tillage at all costs is not necessarily the answer.
“In my mind it is about using all the tools you have to be able to establish the crop,” he said.
There can be situations where a field would have established better if it had been cultivated before direct drilling.
Equally, there are circumstances where too much cultivation can create problems.
“There are also situations where ploughing and combi drilling involve too much cultivation and soils become too fine and cap,” David said.
His advice is to assess each field individually, monitor the weather and select the cultivation system that gives the crop the best possible start.
Right tool, right time
David’s approach can be summed up simply: “Right tool used at the right time.”
In good soil conditions early in the season, direct drilling with either a disc or tine can work effectively.
In wetter conditions, however, ploughing followed by combi drilling may provide a better route to establishment where direct drilling risks smearing the soil with the disc or tine.
The same principle applies on steeper land where surface run-off is a concern.
Direct drilling, with stubble left intact, can help reduce run-off and provide protection for the soil.
For David, strategic tillage is therefore not about choosing one cultivation system over another.
It is about understanding the strengths and limitations of each approach and matching the system to the field, crop and weather.
The priority, he says, should be achieving successful crop establishment while using the appropriate tool for the conditions in front of the farmer.
Share