Harnessing the power of good soil structure for effective black-grass control in potato crops
COMPACTION caused by last season’s wet weather will exacerbate black-grass issues unless it is dealt with, warns independent soil and cultivations expert, Philip Wright.
Across the country Philip is seeing many soils with a solid surface layer, which could make achieving a fine consolidated seedbed tricky this autumn.
“Rain pummelled the soil’s surface, loosening small soil particles which have been washed into the soil’s profile and accumulated at around 7-10cm – effectively the soil, viewed as a filter, became blocked,” he explains.
“With the summer’s weather drying out the soil surface, many acres now have a layer that’s as hard as concrete on top,” he adds.
Philip describes how heavier soils have shrunk and cracked in the summer’s warm weather, and most machinery will break up the ‘crazy paving slabs’ into large clods.
“When it comes to black-grass control, everything with a cloddy seedbed is wrong – there’s poor crop establishment, reduced pre-em performance and protracted emergence of grassweeds,” he says.
BASF Business Development Manager, Stuart Kevis agrees: “The better the soil structure is, the happier the seeds are to get up and going. For grassweeds that means better take up of residual chemistry. For crops, it’s about robust establishment leading to more competitive plants.”
Generally, growers are advised to check for blackgrass in the autumnto to confirm whether they are facing a potential issues ahead of planting for the following season’s potatoes.
Controlling grassweeds post-emergence of potato crops can be very variable. Industry experts have frequently advised that if problematic grassweeds are expected in a ware crop, it is best to be prepared and have a pre-emergence glyphosate product in stock. The current expiry date for UK use of glyphosate is set to be December 2025 and in a recent study, Rothamsted’s Dr Helen Metcalfe said its use is central to no-till farming approaches therefore it needs to be replaced in agricultural systems.
How to best deal with the current soil situation is field dependent, according to Philip, however the general principal is to keep cultivations low disturbance. Deep or aggressive cultivations will only result in large clods.
“A robust tine-based drill might do the job where the layer of compaction is shallow – 5-6cm deep, for example. This would be ideal ahead of a cover crop where there’s the opportunity to control germinating black-grass.”
Philip says growers also have the option of slightly deeper tine cultivations, followed up by a low-disturbance disc-based drill.
“This approach will work well for covers ahead of spring crops where there is more time to control germinating grassweeds. It could also work for winter crops, though delayed drilling and stale seedbeds will be crucial, and that might not be popular after last season closed in so quickly.”
Now conditions are wetting up a little, Philp thinks there’s scope for field-by-field decision-making.
“Shallow disc cultivation to create fines is OK provided the soil is not too damp to smear,” he says, adding: “Tine openers can work through this zone, provided disturbance levels are not high.
“If there is porosity through the soil profile, there is potential for soils to crumb and there’s still a chance for minimum cultivations,” he said. “But do check tyre pressures, there’s nothing worse than using low-disturbance machinery, only to find high disturbance in the wheelings where eradication is needed.”
Pictured: Independent soil and cultivations expert, Philip Wright
