Arable
Be clever about post- harvest cultivations
• Consider what else your soil needs
• Plan ahead and test for compaction
• Don’t rush in unless it is necessary
T
imely and well-chosen post-har- vest cultivations will help make soils more resilient to wet and
dry conditions, says agronomy fi rm Hutchinsons. In the rush to prepare for drilling, it can be tempting to go straight in with the cultivator or subsoiler as soon as the combine leaves the fi eld. But do- ing so may not be best for soil health or crop establishment. “Before doing anything, it is im- portant to stop, take a step back and consider what the soil needs,” says Hutchinsons head of soil health Ian Robertson. Growers should adopt a fl exible cultivation strategy, he says. “Clever cultivation can mean any- thing from not cultivating at all to sub- soiling 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.”
Low disturbance subsoilers are in- creasingly popular for rectifying struc- tural issues in shallow tillage systems. Such implements are often needed to break up distinct layers that can form where ground has been repeatedly cul- tivated at a shallow depth..
Soil requirements
Cultivating repeatedly at about 50mm can restrict water infi ltration and root growth. But the need for remedial ac- tion can often be avoided by adopting a more varied approach to cultivations in the fi rst place. The fi rst step in deciding whether any cultivation is required is to dig a few holes. Then identify whether any structural issues need addressing. These can include problems such as compaction or poor drainage. Soil assessments are usually best done in spring or autumn when ground is moist and warm, with active root
18 ANGLIA FARMER • AUGUST 2021 How bubble test can assess soil health
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. A simple “bubble test” could avoid unnecessary
tillage, saving time, money and benefi tting natural soil structure. It works on the principle that good soil structure typically comprises 25% air, 25% water, 45% minerals and 5% organic matter. Growers should place a lump of soil – around the size of a house brick – in a bucket of water. A steady
stream of bubbles shows air is being displaced from natural cavities and pores, so soil structure is likely to be dry and hard, rather than compacted. A lack of bubble activity could suggest air pockets
have been destroyed by compaction and remedial action is needed. The test isn’t infallible but it is a sim- ple way to stop a lot of recreational tillage. The process also doubles as a slake test, which in-
dicates the stability of soil aggregates. A soil which dis- integrates easily has a poorer structure and lower or- ganic matter than one that remains intact.
growth and biological activity. When assessing soils in summer, care is need- ed not to mistake dry, hard soil for be- ing compacted. The bubble test (see panel) is a sim-
ple way of identifying whether dry soils are compacted. Infi ltration tests are also useful, but when conducted in summer, make sure water does not fl ow straight down cracks, says Mr Robertson. “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 do a
fantastic job of stabilising soil aggre- gates. They also improve the porosity and structure of the top layer that crops are drilled into, so leaving this undis- turbed can often be a better choice. Nine times out of 10, the top 50mm is actually in good condition, agrees Hutchinsons technical manager Dick Neale agrees. “Stubbles generally han- dle moisture much better than a culti- vated surface,” he says.
“If you’ve got a nice friable surface that has managed moisture well, most modern drills are capable of drilling di- rectly into stubble, so there’s no need to cultivate. Cultivations destroy ag- gregate structure, which takes time to rebuild.”
Not disturbing the surface offers
signifi cant benefi ts for moisture con- servation too. This can make all the dif- ference when establishing crops such as oilseed rape or early-sown wheats in dry autumns, adds Mr Neale. “Moisture conservation and man- aging moisture within the seedbed have got to be an absolute focus. Oil- seed rape in particular is better di- rect-drilled with a disc or tine-based implement to minimise soil movement and conserve moisture.”
Given the importance of even sow- ing depth for such a small seed, Mr Neale advises against seeder units on subsoilers. Growers should plan rota- tions and cultivations carefully to en- sure any structural issues are rectifi ed in preceding seasons, he says.
Target cultivations
If soil assessments reveal some form of cultivation is required, both experts urge growers to select operations and implements suited to the specifi c soil requirements.
“If compaction is iden- tifi ed, consider where it is, how extensive it is and what depth it is at, so machines can be set- up correctly to address this,” says Mr Neale.
“Don’t assume poor water movement from the surface is due to deep com- paction and poor drainage; it may be a surface issue that’s easier and cheaper to rectify.”
Many soil wa-
ter management problems in re-
Autumn
cultivations should be
carefully timed and chosen
Below:
Cultivation depth should vary year on year, says Ian Roberton
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