14 February 1997

Limes future looks high-tech

LIME spreading is a black art. But it cant stay that way. That was the view of Rod Baker, managing director of Amazone, at the National Lime Demonstrationat Codsall Wood near Wolverhampton last week.

Independent fertiliser consultant Chris Dawson echoes the message. "There is a growing awareness of the need for more accuracy, even if it means spending an extra 50p/acre."

Lime spreading contractors at the event felt precision farming would make it necessary to target lime application even more carefully. If not it could restrict the optimum uptake of carefully planned and applied nutrients due to over or under application of lime causing lock-up or increased availability.

There is no evidence that tray testing is used to assess the evenness of application, acknowledged the Lime Producers Council.

An ADAS trial shows the amount of material passing the statutory 150 micron sieve can vary in size greatly. A 40% variation was found for ground limestone, 19.8% for screened limestone and 17.9% for coarse limestone. Some particles ranged up to 5mm in size, adding to the chance that spread patterns may vary.

"However, compared with fertilisers there is more latitude for rates to vary because pH is a logarithmic scale," comments Mr Dawson.

ADAS trials have shown that fine ground lime gives the best agronomic results, added Mr Baker. However, windy conditions can cause environmental and spread problems. "We have overcome these with auger-fed dribble pipe booms of up to 12m (39.4ft) wide, which lay the lime on the ground." That technique is only suitable for fine samples which are of low moisture and stone-free.

In other circumstances, and for most of the spreading in the UK, belt-fed twin spinning discs are used. These need modification – at a cost – to meet the more precise needs determined by GPS-based sampling systems, pointed out Brian Annis of Needham Chalks, Suffolk.

"Farmers in the eastern counties are no longer prepared to accept the ADAS figure of pH 6.5 given in most of their literature. They are looking at pH 7.0-7.5 for sugar beet, barley and rape in particular," Mr Annis added.


LIME TIME


&#8226 How precise is lime spreading?

&#8226 How precise does it need to be?

&#8226 What is optimum pH for sugar beet, barley and oilseed rape?

&#8226 Fine grind needed for speediest agronomic effect from limestone.