Wednesday, 24 August 2016

Should potato crops be hardened up so they root deeper?

On August 18th SPot Farm West, James Daw’s farm, welcomed two specialist groups. 

Morning saw the ‘Next Generation’ and the afternoon welcomed the Independent Potato Agronomists. 
Facetious AHDB staff commented on the considerable difference between the average age in the morning and that of the afternoon.

Both youth and experience however, asked the same questions to Mark Stalham of NIAB CUF who was discussing irrigation:

  • “Should potato crops be subjected to some level of drought early in life, to make them use water more efficiently?”  
  • “If a crop is too well irrigated will rooting be weak and shallow?”

As a scientist Mark tends to answer questions in detail, giving the evidence for both sides of an argument. This time the two sides weren’t equal and the answer was clear. 

‘The best way to stimulate root growth is to irrigate the crop, provided there's no waterlogging’.

Toughen up scientists, not potatoes

Mark Stalham referred to an experiment he had conducted on Cara, where the maximum root length came from the fully irrigated crop.  

The length was 15 km of root per square metre of soil, compared with 7 km per square metre for the fully droughted crop (or one which was droughted until the end of tuber initiation then irrigated). 

The experiment took place in 1992, when Mark was in the ‘Next Generation’ category. Measuring those lengths probably hardened him as a young researcher.

Though, as is often the case, there is some truth in the commonly held idea that the plant should be made to work for its water. 

In Mark’s experiments, rooting depth was increased 10-15 cm by drought but the deeper rooting was compensated by root death in the surface layers.  

So whilst droughted plants do change their metabolism to use water more efficiently, both increased rooting depth and altered metabolism only take place when the plant is under significant drought stress and yield has been severely damaged. 

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