Satellite-guided variable rate nitrogen applications have shown enough promise in trials to persuade Hampshire farm manager Tim Walters to adopt the approach on all his wheat next spring.

Mr Walters, who manages the all-arable 607ha (1500-acre) Upton Park Farm at Old Alresford, believes the gains will more than offset the system’s costs.

Although the estate lies over chalk, it has a wide range of soils and until 2000 had a dairy, which lifted the fertility of some fields. “The soil variability is enormous, even within fields.”

The first step involved adjusting phosphate and potash indices more precisely. Until he approached SOYL’s Simon Parrington in 2005, Mr Walters’ adopted an insurance strategy based on standard W-pattern soil sampling once every three years plus guidance from DEFRA’s RB209 booklet.

Tim Walters (right) and Chris Mellish are enthusiastic about extending the idea to nitrogen use.

The latest, more intensive, SOYL GPS analysis (based on 16 samples a hectare) allows corrective treatments to be simplified using just three straight fertilisers – muriate of potash and triple super­phosphate plus kieserite where magnesium is needed.

“We’ve found and treated pockets of nutrient requirement that would never have been picked up with conventional sampling methods,” says Mr Parrington.

The new maps also highlighted significant parts of fields that need less or even no fertiliser. The annual saving in fertiliser alone has been 60t, with costs cut by about £18/ha for an outlay of less than £5/ha, calculates Mr Parrington.

Encouraged by those results, with no apparent yield losses in the wheat, spring barley, oilseed rape/winter bean rotation, Mr Walters was tempted to test the SOYLsense variable rate N system.

It uses regular near infra-red satellite pictures to assess crops’ leaf area indices, from which appropriate dressings are calculated using the HGCA wheat growth guide. Results and recommendations are emailed to the farm office and the information is used to adjust the spreader’s application rates on the move via a hand-held computer running Farm Works software.

“I was quite sceptical,” he says. “So I decided to split one field of each of our three wheat varieties, do our N dressings as normal on part of them, apply Simon’s system to the rest and compare the results.”

The outcome was that in all varieties, plus one test field of ES Astrid oilseed rape, the SOYLsense system boosted gross margins.

Mr Walters, who plans to use the new system across all his wheat this season, believes it should leave him better placed to justify his nitrogen use under any tighter NVZ rules.