Thursday, 28 July 2016

The whole system approach to chitting maincrop at SPot Farm West 2016

The decision to compare chitted versus unchitted seed, in Markies and Pentland Dell, developed from a conversation between James Daw and Matt Smallwood of McCain Foods last year.

James and Matt saw chitting as offering some insurance against bad weather. 

If spring is late or autumn early, especially in relatively clayey soils, late maturing varieties are likely to be harvested in difficult conditions. 


All varieties of course have their own characteristics and respond in different ways to production processes. 

For these varieties, some considerations in particular are that Markies require a long bulking period (>120 days), followed by skin setting, and Pentland Dell can’t be planted into cold seed beds to protect against little potato disorder. 

So marketable yields in both these varieties may potentially be reduced by a relatively short growing season, making them well-suited to test potential benefits from chitting.

James Daw was also hoping to increase total yield beyond what could be achieved from unchitted seed even if the season proved to be a good long one.


Our understanding of chitting 

The principles of chitting have been understood for many years. 


By starting growth pre-planting the crop emerges sooner. The effect of even a few days gain in early canopy is magnified by the long days at which it takes place. 

In this case there was an 8-10 day reduction in time to 50% emergence due to chitting.

The trial field at Thorpe Constantine does not suffer from free living nematode or Rhizoctonia damage, but where these problems are expected then reduction in time to emergence from chitted seed reduces the most susceptible periods.


Chitting as a whole system

To be viable, chitting ought to be fully mechanised. 

Sam Daw designed and made new modular trays for this purpose, shown below.







Interest in tray design

On July 19th the Daws placed a set of their modular trays on the edge of the trial field, to show visitors. 

Guides trying to stick to a timetable as they steered groups around the Open Day demonstrations were thwarted when they reached these trays! 

Clever features of the design were admired and phones came out to take pictures.




Each set of four has the same footprint as a one tonne box, and takes half a tonne of seed. Sets can be stacked six high. 

The four trays can be locked together and have removable sides for when the seed is being tipped into the planter.


Setting the right conditions for chitting

At the Daws’ farm part of a grain store was sectioned off with polythene for the chitting process, lit with fluorescent tubes and LED lights to provide the 10W/m2 required. 

The target for the chitting period was to provide 200-250 day degrees, since excessively early chitting could lead to premature senescence, so the trays were set up at the end of February. 

Temperatures were 10-12°C in the shed. 

LED lights have the advantage of giving off little heat and strings of them were attached to some of the trays, to illuminate without overheating the seed below.

The seed was removed from the shed and left outside to harden off in natural light from mid April, before planting on April 28th

Such hardening off is essential to avoid bruising or breaking the shoots, which were approximately 10mm at planting.

Other requirements for the system are a gentle transfer mechanism into the planter, and use of belt planters.


Results

By July 13th the yield from chitted seed was 7-8t/ha greater than that from unchitted. 



Further information, including treatment effect on size fraction, marketable yield, dry matter and processing quality, will be available at the ‘results day’ in early January.

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