in nutrient spreading

31 January 1997

Farm advance

in nutrient spreading

Precision farming claims to offer growers many benefits, but sceptics remain. Charles Abel, Andrew Blake and Robert Harris report some of the latest developments in the sector

SPATIALLY adjusted fertiliser application came a step closer to common usage last week with the launch of a system for applying variable rates of two nutrients at the same time, using conventional farm equipment.

The Twin Opti from Hants-based SOYL aims to replace the Terragator. It uses front- and rear-mounted fertiliser spreaders operated by SOYLs own control boxes.

"Twin Opti puts variable rate technology into the hands of far more operators," comments Mark Glyde, managing director of SOYL. The variable applications it offers can bring savings of up to £24/ha (£10/acre) in fertiliser costs alone, he claims.

Those come from avoiding over-application to areas of the field where the nutrient status is already acceptable. Added to that are yield improvements where nutrient supply is stepped up in deficient areas.

Initial mapping costs about £16/ha (£6.50/acre). That includes the field layout and sampling, plus soil analysis for P, K, Mg and pH and creating application maps. Sampling is on a 100m grid using the SOYL Mobi GPS system mounted on an ATV.

Contractors then typically charge an extra £1.80/ha (75p/acre) for operating the Opti system, which adjusts nutrient rate for each 25m square block of the field. That reflects the £8200 capital cost for SOYLs Twin Opti system and the 5-10 minutes downtime needed to load data between fields, explains Mr Glyde.

According to Harold Makant of SOYL agent Banks Doltons, based at Newbury, variable rate applications are justified wherever nutrient status varies by more than two or three index bands across a field. Every SOYL recommendation includes a consideration of cost/benefit, adds SOYLs Simon Parrington.

A key part of creating the application maps is data from the farmer. That is used to create a nutrient balance each year, to show expected off-take and required inputs. Original maps can then be used for up to five years before repeat testing is required.

Information from the farmer includes soil type, cropping, yields, normal fertiliser policy, preferred products and the desired nutrient regime in terms of desired index and frequency of application.

The SOYL Mobi mapping system now uses differential GPS, giving an accuracy of 1m (3ft). That means sampling sites can be revisited in subsequent years to see how variable application is affecting soil nutrient status.

Sampling itself is enhanced by collecting 16 sub-samples at each point, adds Mr Glyde. "We used to collect 10, but research in the UK is now suggesting 16 is more appropriate, giving 90% accuracy. In the US they use just 5. Over the coming year we will be checking 10, 15 and 20 sub-samples, to see just how many we really need."

SOYL has already mapped 81,000ha (200,000 acres), says Mr Glyde. "The SOYL Opti system will help us treat a lot more of that mapped area."

Variable rate Pand Kspreading cut costs by £10/ha for Hants farmer Andrew Blanchard (left) seen here with Harald Makant of SOYLagent Banks Dolton. SOYLs new Twin Opti spreader set-up stands behind.

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