Desiccation 2020 – what to consider before you plant

Friday, 31 January 2020

As we head into the first season without diquat, our Strategic Farm North host Will Gagg and three members of our Knowledge Exchange team reflect on the decisions that need to be made before this year’s crop goes into the ground.

Bed formation and machinery set-up

Machinery specialist Harry Henderson says that an easy mistake to make would be to forget to check bed formation against flail set up. “Destoners and planters operate on a single bed, but flails may operate over two or three beds, so it’s going to be really important to match the topper to the rows – just a few centimetres out will make a big difference,” he says.

It’s a trap Will, who has bought a new flail after showing four options at a SPot North demonstration day, is making sure he doesn’t fall into. “We were very conscious how we set out the beds and rows when we looked at buying a flail topper. On our Wold soils we opt for a 80cm (32”) row on a 180cm (72”) bed, whereas on the silt soils we move to a 90cm (36”) row on a 180cm bed. We’ve had to buy a topper that can accommodate both row types,” he says.

David Wilson adds that ensuring beds are aligned now will save vital time at harvest. He said: “If you’re using GPS and you’re ridging three beds at a time, then you run a destoner up every single one it could move them slightly and you’ll end up a couple of inches out when you go back in with your three bed system.”

Field layout

Another consideration is leaving enough space to turn a flail at the edges of fields, this may mean you choose not to plant headlands this year, or at least you will need to consider where to leave breaks. Will said: “Where we do plant headlands we’re going to leave a much wider break of 5-6m so that we can get the flail in and out easier.”

One of the worries about relying on a flailing system is the effect a wet season would have on harvesting, he points out. “We’re going to have to increase our ability to grade and harvest in better format as I can see costs increasing by 12-16% depending on the conditions at flailing.”

Nitrogen rates

Research and trials work over the last few years has shown that many growers could afford to cut back on nitrogen without suffering any yield loss. One take home message has been stick to the RB209 recommendations and cut the ‘insurance dose’.

The challenge of desiccation could bring your N rates into sharp focus. Bill Watts said: “The more vigorous the crop is when you want to take it down, the longer it will take to set the skin - the tubers aren’t ‘thinking about skin-set’.

“We did work on this in 2018 and we saw a direct link between a lower N rates and a quicker skin-set. Maris Piper at 120kg/ha, had progressed twice as far as the same crop at 180kg/ha.”

Variety choice

While there is often limited variety choice for growers, knowing your cultivar and controlling the controllable is important. Indeterminate varieties will require particular care when it comes to nitrogen rates and desiccation.

Will Gagg said: “We’ve been cutting back on N across the board as a result of work with Dr Mark Stalham through AHDB’s SPot Farm network. There are some varieties where the reduction will be significant.

“We’ve included two new varieties this year, Manhattan and Kingsman and we’re increasing other varieties like Melody and Saphire.”

When deciding what variety to plant where, desiccation is a factor to consider. Some soils will not bear the weight of a flail well under wet conditions. Such land is better planted with varieties that are easier to finish, with the difficult indeterminate varieties allocated to drier more resilient fields.

Further reading

The cost of desiccation without diquat Latest potatoes podcast - desiccation and storage in 2020