2 June 1995


SOME fields at Shuttleworth have had three years yield mapping already. The project started with four fields in 1992; this year, 120ha (300 acres) are under satellite scrutiny.

Benefits have already been found. Soil compaction in Black Hut Field following a late maize harvest saw yields plummet; satellite mapping identified the worst hit areas and the scale of the impact on yield.

Feed wheat drilled into good seed-bed conditions gave an output of 8.5-9.5t/ha (3.4-3.8t/acre). Compacted areas managed just 4-6t/ha (1.6-2.4t/acre).

While admitting experience would have suggested a yield slump was likely, Mr Welti found the precise yield maps helped confirm the extent of his fears. "It means we can match our input decisions to the potential profitability of an area," he says.

That is clearly demonstrated with the farms set-aside policy. Yield maps show some headlands, particularly alongside woodland, are very unproductive. Low yielding contours stretch up to 36m (120ft) into fields, with rabbit damage a particular problem in places.

Flexible set-aside

This year flexible set-aside has been used to establish non-rotational set-aside on 25.2ha (62 acres) of less productive headlands as identified by the yield maps. "It has probably increased revenue by over £3000," says Mr Welti.

The maps are also being used to investigate other less productive areas within fields. They allow soil compaction, pH, P and K testing to be targeted rather than following traditional techniques, Mr Welti explains.

The physical soil characteristics such as compaction affect yield variations within fields more than the chemical characteristics, such as P and K. It is more benefit to invest money in sub-soiling rather than expensive soil sampling at the moment.

Last year for the first time the combines GPS satellite positioning system was also used to record the position of weeds in fields. The combine driver, who is well placed to spot areas of weed in the crop, logged weed patches as the crop was harvested.

The resulting maps compared favourably with ones produced by Silsoe Research Institute workers using a "back-pack" mapper. "It showed that a spray treatment map derived from either weed map would be almost identical. The yield map data generated at the same time has enabled us to assess the effect of the weeds on yield," says Silsoes Dr Paul Miller.

The weed maps produced from the M.F. combine were used this season to evaluate the SRI patch sprayer. This uses GPS information to switch on and off and adjust product and application rate across the field.

Other fields have had the variable rate approach applied to drilling and fertiliser spreading. The equipment used in that work was an MF3120 tractor fitted with GPS, working with a variable rate Nordsten pneumatic drill and a KRM Bogballe fertiliser spreader. By pre-programming data from the yield maps, rates were adjusted automatically during application.

Mr Welti is yet to be convinced of the merits of adjusting seed rate according to GPS maps. He also believes that precision farming will be most practical if applied to tramline widths. "Expecting to adjust inputs every 2m across each bout is just too much to ask," he says.

"I think the greatest benefit of variable inputs will be in reducing inputs on inherently less responsive areas of the field and increasing them where you know there is a 12t/ha yield potential, which can justify the investment in increased inputs."

Visitors to Cereals 95 will be able to find out more about the techniques and applications involved from various exhibits at the show and a special conference in the early evening of Wed, Jun 14. Turn to page S6 for more details.