Better management of your Nitrogen

Back in 2001, the first commercial N-Sensor became available. Nine years on and while the system has yet to make an enormous impact on farming practices, its ability to allow better nitrogen management in an increasing number of crop types is well recognised.

The logic behind the Yara N-Sensor system is the fact there can be a wide variation in the availability of soil nitrogen and where nitrogen levels are low plants tend to look less green and their growth not so lush.

These variations can be caused by water movement, previous cropping or even where muck or slurry has been spread.

It all adds up to different nitrogen levels across a field and, as a result, a crop which is unlikely to yield to its maximum potential.

The N-Sensor’s developers set out to find a way of measuring these variations and, by assessing the amount of nitrogen required to even up nitrogen availability, improve the evenness of ripening, produce better grain samples and increase yield overall.

The device uses sensors to monitor the density, height and colour of the crop canopy as different colours have different wavelengths.

Using sensors ,which pick up reflections of a particular wavelength transmitted by the unit enables the colour of the leaf to be determined and, as a result, the amount of nitrogen required. The canopy density is also detected by analysing the reflected signal.

In all, four sensors attached to the top of the cab as a single unit, are employed.

Scanned area

The system scans a crop area of about 50sq.m every second as it moves through the crop, the results received are translated into the nitrogen volume required and then, through a control system, to adjust the spreader’s application system accordingly.

Early N-Sensors were affected by changes in ambient light, bright sunshine, clouds and so forth, so a fifth sensor was fitted to register light conditions and provide additional information which could be factored into the computer’s calculations.

But there were still limitations. Daylight was always required for it to work; when the sun was low or light levels were poor, it was time to retreat to the barn.

This was bad news for those who needed to work longer hours so in came the Yara Active Light Source (ALS), which is able to produce its own light source and make it immune to the availability of day light.

For this it uses Xenon flash lamps whose light is reflected back to the sensors and analysed in much the same way as before. The only limiting factor now would appear to be the presence of dew or rain drops on the leaf which can upset the results received by the sensors.

The latest development is the use of smaller sensors, which are smaller and less likely to be hit by low branches. More importantly, these sensors have been designed to allow measurements to be taken from either side, allowing different application rates. Whether a granular spreader can utilise this, or not, is unclear.

However, with sprayer booms now becoming ever wider and granular spreaders able to cope with wide working widths, this ability is seen as a logical and necessary move if accuracy is to be maintained.

The number of crop types that could employ the N-Sensor is also increasing as Yara works to expand its use away from cereals. Growers of oilseed rape, potatoes, maize and onions can now all use the unit to assess where and how much nitrogen should be applied.

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