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Putting potato agronomy to the test - John Swire - Agronomist & Arable Farmer

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Six different aspects of agronomy are being examined at the Hutchinsons Fenland potato demonstration on A.L Lee Farming Company's Friesland Farm near Mildenhall in Suffolk, which opened its doors to growers in early July.

Some of the biggest visual differences are in the herbicide trial, which tests the crop safety of eight post-emergence treatments on a range of 15 popular maincrop and second-early varieties.

Several varieties showed good tolerance to certain treatments, despite not necessarily having manufacturer support, while others have shown more adverse effects (such as scorch and mottling), particularly where higher doses or 'hotter' treatment combinations were used.

Given limited screening of new varieties by herbicide manufacturers, trials such as this provide a valuable insight into the options available where crops are under high weed pressure, says root crop technical manager Darryl Shailes.

"On this fertile soil, many varieties are fairly tolerant until you get to the higher doses or certain combinations of products, when bigger differences start to show," he says. "But even on this forgiving land, moisture stress had a big effect this year. We've seen more adverse effects from all treatments, with crops taking longer to grow away from damage compared with last year when there was more moisture at the right time. So, a benefit versus risk analysis always needs to be done and it may be different every season."

Seed Treatment Benefit?

Dry weather in June and July also highlighted possible physiological benefits from the strobilurin and SDHI chemistry used in the seed disease management trial.

A range of seed treatment and in-furrow options is being tested on plots of Markies planted on May 3. Although all emerged quickly with no discernible visual differences at first, Farmacy agronomist John Chamberlain observed an average of 1.5 more stems where SDHI or strobilurin chemistry was used.

He adds: "More stems generally means more tubers, so it will be interesting to see if differences carry through to harvest when we will assess yield and quality."    

As part of the trial, soil pathogens have been assessed with the new FungiAlert service, which uses soil sensors and lab analysis to detect and identify a range of microorganisms.   Alongside a mixture of pathogenic types, a ‘surprising’ number of beneficial microorganisms were found, many of which have associations with bio-control agents.

FungiAIert co-founder Dr Angela de Manzanos Guinot says the fast  turnaround of results from the in-field sensors could greatly improve the timeliness of soil health analysis over traditional sampling, allowing for more targeted, preventative action.

Comparing seed lots

Further clear differences are apparent in the seed age trial, run by Stefan Williams of Farmacy, who provides agronomy advice at the host farm.

The trial is examining how the chronological age of Scottish Maris Piper seed and different physiological ageing methods affect stem/tuber number and marketable yield.

Two seed lots were used; the 'older' seed had a 50% emergence date of May 5, which was around a month before the 'younger' seed lot. Four ageing treatments were used, including taking seed straight from store and warming for 24 hours before planting, four-week chit, eight-week chit and eight-week chit with chits then removed.

Initial findings show that across all four physical treatments, the younger seed produced 27% more stems on average than the older seed – 4.5 per plant compared with 3.5.

There were also clear differences in speed of emergence between the physical ageing treatments, with the ‘cold store’ and ‘chits knocked off’ plots noticeably slower to get going.

Historically the farm has chitted seed for 8-9 weeks, but doing so risk more damage to larger chits on the planter, which increases crop variability as we’ve seen in the trial,” Mr Williams says.

“Potatoes use a lot of energy producing chits, so you need to protect them.  Knocking chits off induces a shock reaction where seed generates more stems, using up energy reserves.

"Next season we may well chit seed for four weeks rather than eight, given what we've found here."

Two further trials investigating varietal tolerance and resistance to potato cyst nematode (PCN) were also repeated at the Fenland site, although under much higher initial pest pressure than 2017.

"Crops were planted late into warm soils, which gave them an advantage over the pest, so there's not much visual difference at the moment," says John Keer, of Richard Austin Agriculture. "The really interesting point comes when we measure PCN counts after harvest to see how they differ across resistant and tolerant varieties."