One size doesn’t fit all – CPM – Ian Robertson, Dick Neale
With many different cultivation options on the market, it's important to match a new purchase with on-farm objectives ...
Quite often in crop production, experts like to give advice based on a ‘normal year’. But with the past few seasons encompassing everything from non-stop rain in the autumn to scorching hot Aprils, it seems that conditions now tend to be anything but ‘normal’.
It’s fair to say that lack of consistency can make forward planning difficult and while the weather is very much out of the hands of growers, something that could help is making soils more resilient to wet and dry conditions.
Soil resilience, and building that resilience, is something that’s certainly in vogue, but knowing where to begin can be rather overwhelming…
However, according to agronomy firm, Hutchinsons, a key starting point is choosing the right post-harvest cultivations. 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 Ian Robertson－ head of soil health at Hutchinsons – says that may not be best for soil health or crop establishment.
“Before doing anything, it’s important to stop, take a step back and consider what the soil actually needs.”
As such, Ian believes it’s important 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 requires.”
With the rising popularity of low disturbance subsoilers for rectifying structural issues in shallow tillage systems, Ian says that 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.” So just where should you start? The first step in deciding what, if any, cultivation is required is to dig a few holes to identify whether there are any structural issues that need addressing, such as compaction or poor drainage, says Ian.
Generally soil assessments are best made in spring or autumn when ground is moist and warm, with active root growth and biological activity. When assessing soils in summer, he says care is needed not to mistake dry, hard soil for being compacted. “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 two years we’ve seen examples where growers have rushed to create a seedbed after harvest, only for heavy rain to make it unworkable and un-drillable later in autumn. 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, he adds. “Nine times out of 10 the top 50mm is actually in good condition.”
Hutchinsons technical manager Dick Neale 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.”
However, if soil assessments reveal some form of cultivation is required, both Ian and Dick say it’s essential 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 set up correctly to address this,” says Dick. “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, Ian adds. “Subsoiling, for example, requires 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’s also important to remember “cultivations create weeds” by stimulating germination and bringing fresh seed to the surface, notes Dick. “However this can be used to growers’ advantage, such as for managing blackgrass, where shallow (50mm) cultivations encourage a chit of black-grass that can be sprayed off before drilling. “Remember though, blackgrass won’t want to grow until September or October, so timing is key.”
Despite the clear benefits of reducing tillage intensity, Dick says that he recognises ploughing can be useful in some situations, such as where there has been a high blackgrass seed return that year. “Ploughing has got to be done well to properly bury seed to depth, and you must be sure you’re not just bringing up another problem in the form of old seed.
“Factors such as delayed drilling for blackgrass control should always be balanced against the need for good crop establishment to maximise crop competition and yield potential.”
The bubble test
When assessing soils in July or August it can be easy to think that a dry, hard surface is compacted and needs subsoiling or other deep tillage. But that may not be the case, says Ian, who has a simple test that could avoid unnecessary tillage, saving time, money and benefitting natural soil structure.
The “bubble test” works on the principle that good soil structure typically comprises 25% air, 25% water, 45% minerals and 5% organic matter.
According to Ian, 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.
“The test isn’t infallible and there are always exceptions, but it’s a simple, easy thing growers can do that might stop a lot of recreational tillage,” he explains.
The process also doubles as a slake test, which provides a simple indication of the stability of soil aggregates and their ability to withstand external factors. “Generally, soil that disintegrates has a poorer structure and lower organic matter content than one that remains intact.”
Top tips for planning post-harvest cultivations
- Identify what soil needs and any issues
- Plan how to solve these issues using cultivations, cover crops, or other options
- Target cultivations, machine setup, and operation, to field requirements
- Don’t confuse dry soil for compacted soil
- Beware of shallow infiltration issues and deep compaction
- Consider whether cultivation is necessary – to rectify why, what for?
- Avoid repeatedly cultivating at the same depth
- Build aggregate stability by keeping roots in the ground
- Don’t overwork seedbeds before drilling
- If conditions are not right, wait. Always have a plan B.