I’m standing in a field in front of what looks like a combine that’s shrunk in the wash. Pipes and tubes are poking out in every direction, in true Heath Robinson fashion, while a header with over-sized sideknives rumbles through a damp rape crop.

The 1.5m cut means this may not be the sort of combine you’d want to tackle a 50-acre field of wheat with. Moreover its price is a hefty £185,000. So why would anyone spend this much on a combine with an output not much greater than a horse-drawn thresher?

Yes, you guessed. Though the plot combine’s dimensions may be laughably tiny, the results and data it gathers are an essential tool in determining what farmers will be growing or applying to their crops in harvests to come.

Crop-science giant Bayer runs four plot combines across the UK; three Sampo Rosenlew machines and a Haldrup C85 machine, new this year.

The company grows about 20ha (50 acres) of trial plots a year, explains crop trials co-ordinator Laurence Oades. Of these, some are herbicide and seed treatment trials, but most are fungicide applications. “For pesticide and herbicide registration, we have to prove that the product works in different areas which means more physical mileage but less plots.”

Each plot combine will rack up a mere 100hours a year, but during that time it spends its life running at full chat with hardly any crop in it. So levels of wear can be high.

The C85 is a four straw walker machine and works in pretty much the same way as a normal combine. But, because every drop of grain counts in a trial, air jets from either side of the header blow the crop directly into the intake auger, while blowers in the elevator speed up the overall crop flow.

All augers are driven by hydraulic motors rather than the usual belts but drum speed is controlled by two cone pulleys, replicating the system used by a conventional combine. Power comes from an air-cooled 95hp Deutz and drive is supplied via a two-speed hydrostatic gearbox with cruise control.

The 1.5m header has been fitted with a 600mm extension plate for rape, however Mr Oades uses this in cereals too for better visibility. “And unlike the Sampo machine, there’s no returns system on the Haldrup, so you’ve only got one go at it,” he says.

“Haldrup supplies all the software and hardware for monitoring samples, however we’ve opted for a military-spec Noax Technologies touchscreen laptop which automatically uploads data as well as saving it to a USB stick.” An onboard printer produces labels for each sample.

Unlike the Sampo, which weighs just 3.5t, this new machine comes in at a healthy 7.5t when full and has been fitteded with wider tyres to ease compaction.

Because this machine is built specifically for sampling, a chute into the cab brings in a sample from each 12m x 3m plot. “This model isn’t the most advanced, however at the touch of a button you can sample yield, moisture and hectolitre weight,” says Mr Oades.