Crop sensing helps reduce N use

Have you considered using crop sensing technology to help pinpoint problem areas in fields or to apply inputs variably, only to be put off by the cost?

Some farmers probably have been – one of the more well-known systems Yara’s N-Sensor Classic costs in the region of £12,000, while the newer N Sensor ALS, which has an active light source allowing it to work 24 hours a day, costs £20,000 to buy, or £6000 to lease for a season.

In contrast, a new system being promoted by Soil Essentials, a precision farming firm founded and run by three Scottish farmers, is bringing a much lower cost solution to UK farmers.

Crop Circle, a sensor made by American firm Holland Scientific, costs just £2495, or when packaged with data logging and GPS equipment, £4000.

An alternative package with Sitemate VRA software from Farmworks offers variable rate application technology for a total, including sensor, of £4500.

The sensor itself, which can be mounted onto tractor, sprayer, spreader or even quad bike, is small – about the size of a large mobile phone – and can easily be moved from tractor to tractor, says sales director Robert Ramsay.

Importantly, it also has its own in-built light source, like the N-Sensor ALS, which is a major advantage over older sensors, which only work in ambient light.

“It means Crop Circle will work day or night, rain or shine.”

Depending on the height it is fixed to on the tractor the sensor will scan between 1m and 2m of canopy per tramline.

“That’s plenty good enough to get a decent picture of what is happening – providing you’re not scanning an overlap or a gap,” says technical director Jim Wilson.

The scan provides growers with crop biomass and chlorophyll content, which can be used to spot problems and help manage inputs.

“It saves time crop walking,” says Mr Ramsay.

“You’re not wasting time walking the whole field because you can go directly to where the problems are.”

With the right software package the information can also be used to make a variable rate application map.

Nitrogen is the obvious target, although growth regulators and fungicides could also be targeted.

Crop Circle will pay for itself quite quickly if growers variably apply nitrogen, Mr Ramsay suggests.

“HGCA research suggested 4-5% nitrogen could be saved by variable applications.

Typically in wheat, nitrogen costs £100/ha, so if the sensor can save 5% of the nitrogen bill, it doesn’t take very long to pay for it.

On last year’s experience that is not difficult.”

The current Crop Circle system doesn’t yet allow for variable inputs to be applied at the same time the crop is being sensed, unlike N-Sensor, Mr Ramsay admits.

“We’re using it as a set of eyes, not a brain.”

Once mapped, fields should be categorised according to wheat or barley growth guide work carried out by the HGCA, Mr Ramsay suggests.

“Areas with a high leaf area index for the time of year will potentially be at risk from lodging, and will need to be managed backwards (ie receive less nitrogen) than the rest of the field.

“Areas that are just right will receive the standard rate, while areas which are behind, but have a chance to respond, will need more nitrogen so they catch up with their ideal leaf area index.

Finally there might be some areas that won’t make it regardless of what you do.”

“On those areas there is no point throwing nitrogen on. It is all about responsible use of N,” Mr Wilson says.

It was a point he learned from testing the system last year on his own farm.

After variably applying nitrogen the maps can be used to highlight how crops have changed.

“In one field, we had a wet area that didn’t respond to extra nitrogen, so we probably shouldn’t have put N on.”

In contrast, on the same field another initially poor area responded so well yields eventually matched the best parts of the field.

“This year, I will push poor areas hard with the first application, and if they don’t respond that will be it,” Mr Wilson concludes.