21 March 1997

Yield maps promising, but dont rush in

PRECISION farming based on yield maps has plenty to offer. But growers should tread warily before making sweeping husbandry changes.

That was the caution from two independent specialists to growers at a Cotswolds meeting organised by O & N Management Systems – a joint venture company between four members of the Association of Independent Crop Consultants.

"In analysing maps do not get confused by computerised wallpaper," warned Dick Godwin of Silsoe College. In theory current mapping techniques allowed extremely precise applications to be made over many different parts of fields. More realistically, he explained, repeated use of mapping over several years would let growers home in on broad areas within fields which might merit different husbandry.

Maps with up to 15 different colours were easily created. But he questioned the value of having so many shades. "Beware of artificial problems created by overuse of computer technology," he said. There were undoubtedly savings to be made, reckoned Prof Godwin. He calculated that a net benefit of about £17/ha (£6.90/acre) merely by identifying the 20% of a field which required subsoiling and the 15% and 20% areas which deserved N levels different from the overall recommendation.

A valuable discovery so far on four different soil types was that rooting depth beyond headlands was rarely restricted. "It probably means that too much subsoiling is being done – even now."

Take care when tempted to buy plug-in yield map-linked equipment to adjust sprayers and spreaders, warned Paul Miller of Silsoe Research Institute. "There is a danger you could undo all the good work you have done in trying to make better applications."

Pressure controllers on conventional sprayers already struggled to cope with speed variations of more than 20% without altering spray patterns, said Prof Miller. "They are not going to like having to adjust for the sort of things precision farming will require." &#42

Host farmer Lord Apsley (left) and crop consultant Diana Nettleton were intrigued by the potential of greater precision outlined by Dick Godwin (right) and Paul Miller. But changes need to be made with care.


PRECISION WORRIES


&#8226 Beware of over-complication.

&#8226 Can sprayers cope with change?

&#8226 How many bands of variation are needed.

&#8226 Fertiliser spreaders need overlap for accuracy – how to cope?

&#8226 Liquid fertiliser more appropriate?