Another ‘eye’ to assist crops

DEPENDING ON your viewpoint, the Yara N-Sensor – a system which uses the colour and mass of a growing crop to assess how much nitrogen fertiliser to apply – is either a revolutionary system set to change farming traditions, or a system not entirely void of mystique and an element of hope.

For Ben Smith, its use for the first time last year has convinced him that the N-Sensor really has something positive to offer.

“Overall, the results have been impressive,” he says. “And, while it is hard to be too specific, I feel we have gained financially.”

Farming 1200ha (3000 acres) at Wantage in Oxfordshire, Mr Smith grows 800ha (2000 acres) of winter wheat with the remainder devoted to oilseed rape and winter beans. Using 200ha (500 acre) blocks, the crop rotation comprises two wheats followed by either beans or rape and then back into wheat.


The N-Sensor arrived at the beginning of last year, in time for it to make the first nitrogen applications to the wheat and oilseed rape. As well as the N-Sensor Mr Smith opted for a GPS navigation system which enables field maps to be made showing crop condition and the amount of nitrate fertiliser applied.

“These maps are far more useful than yield maps,” he points out. “They highlight areas of poor growth and poor germination at the right time – by the time you get to harvest it”s too late and the information has been tainted by previous operations.

Fertiliser is applied as a farm-mixed 20% urea solution using a trailed Berthoud sprayer. The sensor unit is attached to the roof of the tractor.

Information regarding crop colour and density is sent to a cab-mounted control box which sends instructions to the sprayer to increase or decrease application rate relative to these data.

The thicker or greener a crop is, the less nitrate is applied and vice-versa.

The idea is that a base application rate is set and then the system either increases or decreases it accordingly.

Mr Smith sets the rate to 500 litres/ha – his normal first application rate – and programmes the unit to apply 100 litres/ha above and below this. “I will admit to a degree of scepticism at first,” concedes Mr Smith. “But these fears were soon allayed as application got under way.

“It is uncanny how the sprayer increases and decreases its application rate as it passes through the field. The only problem we had was that on occasions, when the system wanted to put its maximum rate on, the driver had to change down a gear to reduce speed.

“The nozzles just couldn”t cope with the upper application rate.”


Surprisingly, even though application rates were constantly being changed all over the field, the amount of nitrate applied was almost identical to the amount a 500 litre/ha blanket application would have used.

“So there was no saving in fertiliser at this stage although I consoled myself that the fertiliser we had used had probably been better employed,” says Mr Smith.

The wheats and oilseed rape were given their first dose of nitrate during February and March with second applications made in April and May.

“It was quite noticeable how much more even the crops were when the second nitrate dressing was applied – the first application had certainly done its job.”

All went reasonably well but Mr Smith discovered there were some light conditions when the system struggled to perform well.

“The system didn”t seem to like a combination of bright sun and the occasional cloud throwing a sudden shadow across the field,” he explains. “There were also times when the sun was getting low in the sky and the shadow from the tractor started to interfere with the sensors. I understand there are some modifications on the way which could help resolve these problems.”


Mr Smith also used the N-Sensor to apply fungicide – setting the system to apply more in thicker areas of the crop.

“There were clearly some savings to be made with fungicide,” he says. “I would think we were getting an extra 17% out of each tank full.”

Mixed in with the fungicide was a growth regulator and care had to be taken that its maximum application rate was not exceeded.

“We set the upper level fungicide application rate as the maximum growth regulator rate so no over-dosing could be made,” he explains. The proof of the validity of the system came at harvest.

“The crops were noticeably more even – both in height and ripeness, which meant our drying bills were reduced,” explains Mr Smith. “The quality was up to standard and yields across the farm were up by about 3% – the N-Sensor may or may not have been responsible for this but it is bound to have had an effect.

“Overall, I think the N-Sensor is a useful management tool which can clearly offer some financial rewards. At 12,000 it may appear expensive but with our acreage, I would expect to see a return within two years.”

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