There’s a fine line between applying too little and too much fertiliser to a crop. Too much, and you’re wasting valuable inputs, increasing the risk of lodging and running the danger of overloading the environment to boot. Too little and you’re throwing away valuable yield potential, leaving the door open to disease and ultimately reducing your gross margin.

That’s where variable rate application and measuring crop demand in real time can bring considerable benefits, according to Farmers Weekly’s Young Farmer of the Year, James Price.

He has been using Yara’s N-Sensor technology for the past four seasons and has recently upgraded his unit to the top-of-the-range Active Light Source (ALS) unit, which can work round the clock.

How does the N-Sensor work?

There are three stages to the N-Sensor system. The first is the clever bit. The N-Sensor operates a bit like a human eye, using light reflectance to measure the amount of chlorophyll and biomass in a crop on a second-by-second basis.

There are five spectrometers on the unit, four at each corner and one pointing skywards to take account of the ambient light level. The sensor is pre-taught the typical reflectance level for vegetation and puts each reading in a particular category, one for biomass, one for how green the crop is, and so on.

This data is then translated and sent to the spreader or sprayer which will then change the rate of application as it goes along.

The beauty of this system, says Mr Price, is that everything happens in real time. “There’s no reliance on yield maps, satellite data or any other historical information. Everything is done instantly from the readings taken from the actual crop.”

On entering the field, the operator selects the crop and does a calibration run to calculate the average sensor reading for the field. “There’s a nitrogen response curve for most arable crops, as well as potatoes, maize and oilseed rape.” All information is displayed on a TopCon X20 controller, which is pre-populated with data via a USB stick or memory card from the farm office.

“Operators then pick a job and field using the screen, tell the machine the target kilos an acre they want to apply and then both minimum and maximum rates.”

For oilseed rape it’s slightly different. Growers have to enter their yield expectation, the growth stage and the amount of dead biomass. “In the UK, because we don’t have so many harsh frosts, this tends to be between 0 and 20%.

Drivers then need to enter a relative biomass cut-off. “This is basically when it becomes unviable to apply more fertiliser to achieve any benefit. The amount applied then defaults to the minimum rather than the maximum.”

All data is stored on a USB stick or memory card and transferred between the tractor and Yara’s own software or Farmade’s Gatekeeper.

Mr Price’s Berthoud Major 32 was converted last year to provide 10 section auto shut-off and variable rate control. “We also invested in a KRM/Bogballe M2W with weigh cell and calibrator box.” It cost in the region of £3500 to convert the 24m Berthoud, he adds.

This is the third season that full autosteer has been used across the farm, and in particular on the tractor responsible for most of his top work, an autosteer-ready JD7530 fitted with TopCon X20 steering kit.

Organic fertiliser

Mr Price spreads a combination of sewage sludge, coffee waste from the nearby Kraft factory, green waste and cow manure, as part of a straw-for-muck swap he has with a neighbouring dairy farmer.

Although happy to use organic manures, his reliance on milling wheat in the rotation means inorganic fertiliser application needs to be as accurate as possible, which can be hard with material that sometimes doesn’t have an accurate analysis.

“All organic fertiliser is spread at a flat rate across the farm, so where the sensor comes in is in subsequent, conventional fertiliser applications.”

“At different growth stages, it’s important to manipulate fertiliser application rates in different ways. At growth stages 20-30, it’s important to maximise tillering across the whole crop, whereas at GS 30-33 you want to maintain yield on the areas that need it, but still target application to areas that will respond. That’s where the biomass cut-off setting is an important feature.”

On average, Mr Price has seen a 3.5% increase in oilseed rape yields and a 3% increase in wheat. For milling wheats, it’s also possible to push proteins up using the technology, he adds.

“Many variable rate systems use the Robin Hood approach – take from the rich and give to the poor. But when you’re looking to up proteins, sometimes you need more of a King John one. The sensor can use both approaches, and when it comes to protein applications, it’s enabled us to push levels up, particularly in last year’s wet harvest.”

N-Sensor facts

• Benefits: Increased yield, targeted protein application, less lodging

• Use: Solid and liquid fertiliser applications

• Compatibility: Compatible with Farmade software, as well as Yara’s own software that allows operators to process maps

• Price: N-Sensor (£15,000 to buy + £500 a year back-up, £3500 a year to rent including back-up) and N-Sensor ALS (£25,000 to buy, £6500 a year to rent including back-up)