27 July 2001

HEAVY summer downpours may reduce the need for irrigation, but potato yield and quality could be hit if producers allow soil moisture monitoring to take a back seat.

Nothing can replace regular moisture assessments, taken at least twice a week, to guarantee crops are safely within critical soil moisture deficits, warns research lecturer Ivan Grove.

Speaking to growers at the BPCs reference crop open day at Harper Adams University College, near Newport, Shropshire, he said new equipment made moisture assessments easier and more accurate.

"If soil moisture levels are allowed to slip, crop performance will suffer. For maincrop potatoes an SMD of 35mm will impact on yield and quality, while common scab can occur with deficits of just 10-12mm. For earlier harvested crops the parameters are tighter, with a maximum SMD of just 25mm," said Dr Grove. "Despite the recent downpours, deficits can still accumulate quickly. Free-draining soils may retain little moisture and crops can easily lose 3-4.5mm a day through evapo-transpiration aided by a good breeze."

"Timed applications of 5mm water across the growing area should keep SMDs within critical levels. But growers are treading a fine balance all the time.

"If SMDs are brought down to very low levels and rain showers follow it could lead to run-off and disease such as powdery scab.

"The use of moisture records is already important, but will become essential in future to safeguard water abstraction licences," he added. "The Environment Agency now wants more information to support applications and producers will have to prove their case." "Growers determining irrigation use by simply feeling a handful of soil are now acting irresponsibly and deserve to have licences rebuked in future," he said. &#42

Spud growers urged to check crops