GPS-driven variable-rate seed sowing saved a Wiltshire farm nearly £3/ha (£1.20/acre) last autumn and has produced some encouragingly uniform crops going into the spring.

The Courtyard Partnership's Intelligent Precision Farming zone-seeding approach, automatically adjusting seed rates to different soil types (Arable, 21 Sept 2007), was used for all autumn drillings at Ramsbury Estate, Marlborough, says manager Duncan Lee.

"If you take this figure over our whole winter cereal and oilseed rape area of 1780ha, we are making a significant saving."

But savings alone can prove a false economy. So has the zone seeding idea delivered?

Clearly, the final proof won't be available until harvest, but initial results look promising despite some less-than-helpful material in last season's seed, Mr Lee believes.

"We were aiming at 650 tillers/sq m, and although the germination level was fine, I have a feeling that the seed vigour wasn't generally as good as we had hoped.

"We normally expect to get 80% establishment, but some has been as low as 60%, and some of the smaller plants have been out-competed by bigger ones."

Nevertheless, detailed counts on two wheat fields after beans - chosen for their relative freedom from rabbits, slugs and other interfering factors - show tiller numbers ranging from 550 to 600 over several soil types.

"The seed rate on the best of these we set at 175/sq m, and it went up to 225 on the clay cap. It was actually slightly lower than it might have been because we drilled on 12 September as opposed to our target of the 20th."

Mr Lee and Courtyard's Vince Gillingham admit there is still much to learn, not least about where to pitch specific seed rates to the soil zones and sowing dates. Last seasons' levels were chosen jointly with Masstock agronomist Jim Hynes.

"We're still on quite a learning curve, but I'm satisfied so far," says Mr Lee. "On one field bank in particular, where we normally expect to see bare soil, we've got a pretty even green crop right across it."

The key question now is how far the tiller numbers can be manip­ulated with variable-rate first nitrogen applications, again GPS-driven, says Mr Gillingham.

"We're still only dipping our toe in the water and building up our experience. There has been so little investment in the R&D needed behind precision farming in the past 10 years that it's very much a matter of suck it and see," he adds.

Mr Lee says an important feature of the IPF system is that it is flexible, allowing the operator - assistant manager Martyn Hall - to modify the planned seed rates if he believes conditions demand it.

"A lot of farmers don't like rigid plans in effect working to the gospel. They want to give the guy on the drill control because he sees every square foot of the field."

That can make seed ordering tricky, he admits. But he quickly dispels any notion that weeds might be more troublesome under zone seeding. "We've seen no difference at all."

• Seed rate adjusted to soil zone
• Significant savings
• Establishment below target
• Low seed vigour suspected