“Clever” post-harvest cultivations
2nd August 2022
In the rush to prepare ground for drilling, it can be all too easy to go straight in with the cultivator or subsoiler as soon as the combine leaves the field – but that may not be best for soil health or crop establishment.
“Before doing anything, it is important to stop, take a step back and consider what the soil actually needs,” says Hutchinsons head of soil health, Ian Robertson (right), who urges growers to adopt a flexible “clever cultivation” strategy.
“Clever cultivation can mean anything from not cultivating at all to subsoiling or ploughing where necessary. As a general rule, never cultivate at the same depth every year and make sure whatever you do delivers what the soil actually needs.”
He notes the rising popularity of low disturbance subsoilers for rectifying structural issues in shallow tillage systems. Such implements are often needed to break up distinct layers that can form where ground has been repeatedly cultivated at a shallow depth (typically 50mm), potentially restricting water infiltration and root growth.
“In many cases, the need for this remedial action could have been avoided by adopting a more varied approach
to cultivations.”
Understand soil requirements
The first step in deciding what, if any, cultivation is required is to dig a few holes to identify any structural issues such as compaction or poor drainage.
When assessing soils in summer, Mr Robertson says care is needed not to mistake dry, hard soil for compaction. The bubble test is a simple way of identifying whether dry soils are compacted. Infiltration tests are also useful, but when conducted in summer, make sure water does not flow straight down cracks.
“Typically, 50% of soil is made up of air and water, so it may be that rock hard ground just needs wetting-up again to return to a friable surface that can be drilled straight into.
“In the past few years, we’ve seen examples where growers have rushed to create a seedbed after harvest, only for heavy rain to make it unworkable. In some cases, it may have been better not to touch it.”
Root networks left by crops, even low yielding ones, do a fantastic job of stabilising soil aggregates, improving porosity and structure of the top layer that crops are drilled into, so leaving this undisturbed can often be a better choice. “Nine times out of 10, the top 50mm is actually in good condition.”
Hutchinsons technical manager Dick Neale (left)agrees. “Stubbles generally handle moisture much better than a cultivated surface. If you’ve got a nice, friable surface that’s managed moisture well, most modern drills are capable of drilling directly into stubble, so there’s no need to cultivate. Cultivations destroy aggregate structure, which takes time to rebuild.”
Not disturbing the surface offers significant benefits for moisture conservation too, which can make all the difference when establishing crops such as oilseed rape or early-sown wheats in dry autumns, he adds. “Moisture conservation and managing moisture within the seedbed have
got to be an absolute focus.”
Oilseed rape in particular is better direct-drilled with a disc or tine-based implement to minimise soil movement and conserve moisture, he says. Given the importance of achieving even sowing depth for such a small seed, he advises against seeder units on subsoilers and recommends growers plan rotations and cultivations carefully to ensure any structural issues are rectified in preceding seasons.
Target cultivations
If soil assessments reveal some form of cultivation is required, both experts urge growers to select operations and implements suited to the specific soil requirements.
“If compaction is identified, consider where it is, how extensive it is and what depth it’s at, so that machines can be setup correctly to address this,” says Mr Neale. “Don’t assume poor water movement from the surface is due to deep compaction and poor drainage; it may be a surface issue that’s easier and cheaper to rectify.”
Many soil water management problems in recent seasons have been caused by issues of consolidation, slumping or capping in the top 100–125mm of soil, not by deeper compaction. “In such situations, there’s no point running a subsoiler through at 250mm deep, as it could make the situation worse.”
Soil moisture content is critical to the success of operations such as subsoiling and mole ploughing, Mr Robertson adds. “Subsoiling for example needs soil to be dry enough for natural fissures and cracking, but if it’s too dry, there’s a risk of bringing up large slabs and creating an uneven surface. If conditions aren’t right, don’t rush into doing it.”
It is also important to remember “cultivations create weeds” by stimulating germination and bringing fresh seed to the surface, Mr Neale says. However, this can be used to growers’ advantage, such as for managing black-grass, where shallow (50mm) cultivations encourage a chit of black-grass that can be sprayed off before drilling. “Remember though, black-grass won’t want to grow until September or October, so timing is key.”
Despite the clear benefits of reducing tillage intensity, he recognises ploughing can be useful in some situations, such as where there has been a high black-grass seed return that year. “Ploughing’s got to be done well to properly bury seed to depth, and you need to be sure you’re not just bringing up another problem in the form of old seed.
“Factors such as delayed drilling for black-grass control should always be balanced against the need for good crop establishment to maximise crop competition and yield potential.” FG
The bubble test
This is a simple test that could avoid unnecessary tillage, saving time, money and benefitting natural soil structure and works on the principle that good soil structure typically comprises 25% air, 25% water, 45% minerals and 5% organic matter.
Growers should dig a representative lump of soil (around the size of a house brick or large handful) and place it in a bucket of water. The appearance of a steady stream of bubbles shows air is being displaced from natural cavities and pores, so the soil structure is likely to be just dry and hard, rather than compacted. However, a lack of bubble activity could suggest air pockets have been destroyed by compaction and remedial action is needed.
Top tips for planning post-harvest cultivations
Identify any issues to rectify
Plan how to solve these issues using cultivations, cover crops, or other options
Target cultivations, machine setup, and operation, to field requirements
Do not confuse dry soil for compacted soil
Beware of shallow infiltration issues and deep compaction
Consider whether cultivation is necessary – why, what for?
Avoid repeatedly cultivating at the same depth
Build aggregate stability by keeping roots in the ground
Do not overwork seedbeds before drilling
If conditions are not right, wait. Always have a Plan B.
