Hard to beat balance sheet

6 July 2001




Hard to beat balance sheet

BPC is on the road this summer, with a series of interactive

potato technology transfer events. Andrew Swallow caught

up with the action at Hethersett, in Norfolk last week

DESPITE all the technology available to modern man, when it comes to irrigating potatoes a balance sheet method is still hard to beat.

That is the message a leading irrigation specialist draws from an in-depth report by Cambridge University Farms commissioned by the BPC.

"The conclusions are horrifying," says ADAS soil and irrigation specialist Bill Basford. "Thirty years after we put a man on the moon we still dont have a soil moisture measurement tool for accurately assessing field-scale irrigation need."

Three tools for measuring soil moisture content were assessed in the report. The Enviroscan results ranged from 43% overestimates to 30% underestimates, the Aqua-flex ranged from 9% overestimates to 21% under and the neutron probe 8% over to 12% under.

Added to the variability in results from such meters, growers must appreciate that they only represent a spot measurement in the field, says Mr Basford. "They do not inspire great confidence."

Tensiometers, which were not assessed in the report, can perform well if calibrated and installed correctly, he adds. However, they suffer the same point measurement problems and in practice are difficult to manage.

"The placement is crucial and they need to be calibrated correctly. Most of them I see these days are lying in the farm office and not used any more."

Overall, he advises growers who are going to use a tool to measure soil moisture content that the neutron probe is probably most reliable. But accuracy suffers near field capacity, it is only available as a contract service and does not measure the moisture content in potato ridges, he warns.

Balance sheet methods, especially the computer services offered today, are hard to beat. "It works well and if it isnt broken why change it?"

IRRIGATIONNEED

&#8226 SMD meters very variable.

&#8226 Point readings a problem.

&#8226 Balance sheets hard to beat.

&#8226 Computer models more reliable.


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