7 November 1998


Working out your crops nitrogen requirements can be a hit or miss affair. So why not let the spreader do the job instead? Gilly Johnson reports.

IMAGINE having a fertiliser spreader, which was smart enough to know exactly how much nitrogen your crop needed – just by looking at it through electronic eyes.

As it went down the tramlines, the machine would match up nitrogen dose to plant requirement, automatically adjusting the spreading rate as it went along.

Such a spreader would remove all that hassle of taking soil samples, and having them analysed for residual nitrogen. It would mean the end of working through complicated nitrogen prediction plans for your crop.

The technology is here. Its now being tested on UK farms for the first time. Initially developed in Germany, its the brainchild of fertiliser manufacturer Hydro Agri. The key component is a mounted sensor system, which then feeds information to a vari-rate fertiliser spreader.

Hydro Agri pioneered the hand-held chlorophyll sensor, the PrecisioN-Tester; the new device takes the science one stage further and is called the PrecisioN-sensor. It uses light reflectance (including non-visible wavelengths such as infra-red) to assess the chlorophyll content of leaves – effectively the greenness – and the total biomass of the crop, which gives an indication of the density of the plant stand.

The technology also makes other measurements, but for commercial reasons, Hydro Agri is understandably reluctant to reveal details.

With one of the trial sites on his farm, Lincolnshire grower Rob Pask has been able to weigh up the smart spreader at close hand. As an enthusiastic convert to precision equipment – Mr Pask was one of the first in the area to go in for a global positioning system (GPS) on his combine – hes keen to see what this new science can do for him.

Mr Pasks priority is to make better use of inputs, in order to boost gross margins. "Were not interested in higher yields at uneconomically higher costs." This means using nitrogen more efficiently, which benefits returns and also reduces any risk of leaching.

One field at Heydour Lodge Farm, near Grantham, with a range of soil types, including both medium and heavy clay, was chosen as the trial site. The inherent variability – yield maps show a spread of 4-14t/ha (1.6-5.7t/acre) – would give the sensor equipment a chance to show the breadth of its capabilities.

As a comparison, the nitrogen management on part of the field was under Mr Pasks standard practice. Although the nitrogen sensor does not need any GPS link-up – it operates independently – plots were harvested with a GPS combine to produce yield maps and assess results.

The sensor equipment was mounted on a front boom ahead of an Amazone spreader, but this caused minor operational delays. For next season a more practical and simpler positioning solution has been found.

The tractor travels at normal speed through the crop, and the sensor interprets reflectance data every second. Depending on what instructions it receives from the sensor, the spreader then applies anything from 0-250kg N/ha.

Three treatments went on. The sensor was used to adjust rates in the later applications; for the early treatment, the visible plant cover is insufficient for the sensor to assess nitrogen need, so a standard dose is used. Hydro Agris PrecisioN-Plan nitrogen planning system was used as a yardstick for the first treatment.

The sensor is calibrated according to variety – in this case Rialto; each wheat has a different chlorophyll fingerprint. The system is able to operate under constantly changing skies. If a cloud comes over, it adjusts the sensor accordingly.

"To be practical, the equipment has to be robust, able to withstand the wet and easy to use," says Mr Pask. "It shouldnt need the help of a scientist to work out the calibration." Hydro Agris head of agronomy, Dr Jim Lewis, is confident that the sensor fits the bill.

Initial errors

Inevitably, this first season has thrown up some initial calibration errors, and these affected Mr Pasks results. According to the company, the cause of the problems has been identified and rectified. But three other sites in the trial series illustrate how the sensor measures up against farm practice (see table). Gross margin comparisons are the yardstick – which means taking into account yield, quality and the total fertiliser applied.

"By adjusting nitrogen rate, the sensor offsets the variation on a site," says Dr Lewis. In some cases this ends up as a reduction in total nitrogen, but not necessarily on all sites.

"Due to the inherent variability in some sites, only about 25% receives the optimum nitrogen when using standard practice," says Dr Lewis. "Whereas the sensor aims to ensure that each part of the crop is fed to within 20kg N of its input/output balance."

Although this work has focused on cereals, the sensor could be calibrated for other crops. Looking ahead, it might also be operated separately from a spreader unit, so that crop requirement data could then link in with GPS mapping and spreading operations. In theory, that would allow fertiliser spreading to be done at night, guided with GPS, and spreading at rates dictated by the sensors data, gathered in the daytime.

For the moment, Dr Lewis says that the sensor could work with any variable rate spreader, or liquid fertiliser system. "We anticipate the equipment will be most useful for large farmers, farmer groups or contractors."

The company is taking the technology forward. Trials in Germany, where the sensor has had three years of testing, confirm that it can be a valuable tool in tightening up nitrogen applications, says Dr Lewis. An announcement on future commercial development of the sensor is expected at the Royal Smithfield Show in December.

As yet, there are no indications of price tag. But as Mr Pask comments, if it can improve his gross margin performance by making more efficient use of nitrogen, then hell be interested – "but at a sensible price…"

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