Monday, 3 October 2016

Farm walk at SPot Farm West, 22 September 2016

The date of the final farm walk at Thorpe Constantine gave a demanding deadline for Matt Smallwood of McCain and Mark Stalham and his colleagues of NIAB CUF to take yield digs. 

Neither man is shy with a fork, and there was some intense digging behind the results provided for the visitors.

Who got it right on cultivation?
A courteous veneer covered, but did not conceal, the competition between Mark Stalham of NIAB CUF and James Daw, the SPot host. As the visitors gathered round these two experts in the Russet Burbank of Field 33, each of them spoke about a ‘best practice’ treatment, but they weren’t referring to the same treatment!

For Mark Stalham best practice is:
Bedform 37 cm, no bedtiller, destone 28 cm

For James Daw best practice is:
Bedform 45 cm, bedtill 45 cm, destone 30-33 cm

The difference between these two ‘best practices’ is not huge, since neither Mark nor James would use a bedtiller on lighter land, and 28 cm is not far away from 30 cm. Nevertheless, there is a difference. The yield results, from digs a few days before the farm walk, might help us decide between them.

Yield 40-90 mm
Yield > 90mm length

A silent scientist? I wondered if Mark Stalham would be bound by his own gag. He couldn’t possibly say that a higher yield showed his preferred treatment to be the best. It would be scientific heresy, in an unreplicated comparison. But we wouldn’t expect Mark to be silent and indeed he pointed out that the higher yield from the shallower cultivation was consistent with results from over 60 experiments over the past 5 years.

Grower far from silent James Daw had the disadvantage of having come to the farm walk following a night shift, but that didn’t stop him expressing himself on this vital topic. He explained that the field barely needed a bed tiller, but the wet spring this year meant bed tilling allowed the crop to be planted without waiting five extra days for drying. The careful, shallow, bed tilling used in 2016 is far from the energetic cultivation used in 2012 which led to drastic slumping that very wet season.

James judged that his preferred depth gives a reserve needed for confidence by the destoner operators, while Mark considers that his preferred depth has such a reserve built in.

Commercial harvest will reveal more.
Digging by hand gives accurate yield figures but doesn’t tell the full story. When ridges slump, a common result is the harvester picking up stones. We will have to ask James Daw later whether this problem occurred following any of the cultivation treatments.

Loose soil is good?
Michael Bubb, a grower near Newport, asked a simple and fundamental question, “Isn’t it good to have loose soil under the seed, for the roots to grow?” It seems obvious that cultivating deeper creates more loose soil below the seed and allows the roots to grow faster. 

In theory yes, in practice generally no.

Mark Stalham explained that as the share on the destoner cuts into the soil the corresponding ‘push back’ from the soil increases with depth. 

40cm is not only 30% deeper than 30cm, but the soil at depth is also denser. In a sandy soil the share causes a compressed pan to form. Where there is more clay content the moister soil at depth is likely to be above the plastic limit and deform into a pan. In both cases, as this pan is dried by root uptake of water, it hardens and can prevent further root penetration.  

In summary, whatever the soil type, deeper cultivation of wet soil in spring tends to produce a compressed zone of soil which reduces potential rooting depth.

Both men are stars!
From an AHDB (Potatoes) point of view both James and Mark are outstanding in the drive to bridge the divide between research and practice.

Not every grower measures the detail of field operations, listens to research, undertakes field trials and comparisons, and makes careful changes. James Daw not only does these things but also shares his experiences widely at farm events.

Not every scientist follows up his calculations, such as Mark’s y=16·3–4·08Ω mm/day (where y is the rate of root penetration and Ω is the soil resistance in MPa), by spending time in commercial fields with growers and machine operators and seeing why Ω is so high. Mark Stalham follows through on his research, which is why there is much to be learnt from him.

Mates all along.
James Daw and Mark Stalham have been collaborating on cultivation since 2007, irrespective of SPot. Their quest for perfection hasn’t ended and at the end of the farm walk they were at it again, spotted in an intense one-to-one about ‘next year’.

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