We’re all used to the notion of GPS variable rate seeding or fertiliser spreading, using yield maps of each field. But now there’s a new GPS-based system that allows cultivators to automatically increase or decrease their depth according to how much compaction there is beneath the soil surface.

The project is being lead by David Whattoff, the agricultural development manager at Berkshire GPS mapping specialist Soyl. He has been looking at the extra diesel that is used when cultivation equipment goes deeper than it needs to and found that the amount can often be considerable.

If you’re stubble cultivating at 200mm depth, he points out, a fuel usage rate of 37litres/hr would not be unusual. Raise the cultivator to 100mm, though, and fuel use drops to 22-23 litres/hr. That’s a saving of £108 over the course of a 10-hour day

But on most farms compaction depth and areas are pretty variable, even within one modest-sized field. So it would be impossible for the operator to know where the good and bad patches were.

But GPS technology – as ever – has some hi-tech cards up its sleeve. By mapping the compaction across the farm using an ATV-mounted penetrometer, Soyl can produce a ‘compaction map’ of the farm.

The next step, says Mr Whattoff, is to fit the GPS depth controller to a cultivator that has an existing depth control system. Now, as the tractor moves across the field, an on-board GPS receiver will know exactly where it is (to the nearest 2cm, if you have an ultra-accurate RTK system). It also now knows exactly where the areas of compaction because that was previously mapped by the farmer or by Soyl. So it’s a relatively simple technological task to get the cultivator to automatically raise up when there’s only minor compaction (typically down to 230mm) and drop down where the compaction is worse (typically down to 330mm).

Soyl has so far tested its variable depth controller on Heva, Simba, Gregoire-Besson Discordon and Amazone cultivators. More trials will be done this spring but Soyl is confident that the system will work with other brands too. It’s easy to install too, adds Mr Whattoff, and will cost around £5,000 when it goes on sale.

There’s an extra potential benefit, too. Yield maps can be used to create stubble cultivation plans showing where the heavy-yielding areas of the field are. Tillage machinery can then automatically increase cultivation depth as it encounters them to help bury the trash.

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