Understanding precision nitrogen application technology may seem daunting, but doing so could pay dividends. Precision farming consultant Clive Blacker explains what's available and how it could benefit your business.
Rising fertiliser prices, environmental regulations and the revision of RB209 mean the pressure to apply nitrogen fertilisers correctly and keep accurate records will continue to grow.
Good farm management is practised on many farms, but few have adopted precision technology to map variability and apply inputs.
Variability can be due to a number of aspects including soil type, previous cropping, historic manure use, but one common cause is soil fertility, with nitrogen availability being the dominant feature. Soil variability inevitably reveals itself within the crop as variable biomass and colour, both of which can be measured using sensor and reflectance technology.
Real time measurement of the canopy during the crop's life has clear advantages and while growers have been encouraged to use canopy management techniques, such as Green Area Index, there have been few tools available to take actual measurements. Remote sensing offers this capability.
What is remote sensing and how does it work?
The principle of remote sensing is relatively simple. When light is emitted onto a surface, some light is reflected (as electromagnetic radiation) and some is absorbed.
The reflected light will be across the whole electromagnetic spectrum, which is far wider than we can see. The spectrum can be split into visible (blue, green and red) and invisible (near infrared, infrared and beyond) wavelengths. Each object (eg crop) has its unique reflectance spectrum and as a result different objects are seen in different ways.
Cereal crops look green because they reflect the green light and absorb the other light wavelengths. They also reflect light more strongly from the infrared part of the spectrum.
The human eye can't detect this, but an infrared sensor can. These sensors have been developed specifically to measure crop reflectance at different levels, to help farmers target inputs more effectively. Broadly speaking, the near infrared wavelengths are a measure of the canopy size, while the visible bands are an indicator of colour. Bringing the two together gives a total green area measurement.
What sensors are available?
There are several sensors available. Satellites have been operational since the 1970s, and ground-based sensors have been in development since the early 1990s. So how do these sensors differ, and what should users know about the technology?
The main difference between sensors is in their ability to collect information. This can be judged in three ways:
Resolution
This is the size of the parcel of information collected, and therefore the area of the field the sensor sees. Satellites can capture large amounts of information quickly, but the resolution can be poor.
Pixels determine the resolution a pixel represents a fixed area or footprint on the ground. These vary, but the most common used for agriculture is one measuring 32m x 32m and therefore looks at a very large area.
Aeroplanes again offer the ability to capture large amounts of data. The amount and quality depends on the height of the plane. A clear limitation to aeroplane and satellite sensing is the inability to capture accurate data in cloudy conditions.
Tractor-based systems can capture information at a far higher resolution than satellites due to their proximity to the crop. Current application technology does not allow us to vary product rates across the bout width so the key element is that the image captured represents the working bout width.
Light
As the sensor is required to measure light reflectance from the crop, it is important to do this accurately. Passive sensors use the sun to light the crop and measure the subsequent reflectance. Sun angle and cloud cover affect these types of sensor.
Some passive systems have the ability to correct for climatic changes during image capture. There are also sensors that are unaffected by the ambient daylight as they emit their own light to illuminate the crop.
Sensors that can only capture information during daylight are classed as passive sensors, while those that emit their own light are termed active.
Wavelength measurement
Some sensors can only capture a limited number of wavelengths, while others have the ability to capture a wide number.
Generally active sensors can only capture a small number of wavelengths due to the difficulty of finding a bright enough light of the required colour for multispectral measurement. Typically active sensors measure between 2 and 4 wavelengths.
Passive, satellite or plane sensors usually measure 4-7 wavelengths while the passive tractor system used by Yara can capture up to 60 wavelengths.
How are these used in practise?
There are distinct differences as to how the various systems are used by farmers. The biggest difference is the timeliness of data collection and application. All planes, satellite and some tractor-mounted systems offer near real time application, which requires data to be captured correctly, positioned and then processed. The information collated is then run through a model to generate a map or recommendation. This data processing takes time and can be restrictive.
One system - Yara's N Sensor - offers a real time solution where data collection, interpretation and application happen during the pass through the crop.
All systems are used during the active growing season at each nitrogen application. The satellite/plane systems produce an actual application map with a nitrogen recommendation associated with the scanned areas, while the tractor-mounted alternatives require crop calibrations, around which the nitrogen will be varied.
All systems will work on cereals, while some can be used on oilseeds and potatoes. Precision application can be used for liquid and solid systems.
What are the advantages of using remote sensing technology?
The advantages are associated with either over or under supply of nitrogen fertiliser. Undersupply will reduce yield and quality, while oversupply can cause lodging, increased disease, late maturity and poor combine performance (10-20% reduced output).
Very little replicated data is available other than that carried out by Yara and HGCA, which have both shown the financial benefits, the former typically quoting a 3-4% yield increase with no extra fertiliser used. At current crop prices, the breakeven position for moving to variable application is about 142-202ha (350-500 arable acres), depending on farm variability.
Case Study
Geoff Hayes - West Norfolk
Growers considering investing in precision fertiliser systems should be clear about what they want from them before getting the cheque book out. That's the opinion of Geoff Hayes, farm manager for Maurice Mason Farms in west Norfolk, who used two N Sensor systems across 2000ha (4942 acres) for the first time last season.
"It's a bit like opening Pandora's box - at the moment we're raising more questions than answers. You need to be clear you understand the information and know what it will be used for. It needs to form part of the whole management system, which means understanding all other aspects of soil quality."
Individuals also need to be skilled and trained, plus machinery has got to be compatible, he says.
Mr Hayes' N Sensors are fitted to two KRM spreaders and work across all first and second wheats, and oilseed rape. The farm's sprayer is fitted with auto boom section control and basic GPS, and yield mapping is also used on the combine.
Total 2007 fertiliser use remained relatively unchanged compared with the previous year, but Mr Hayes says it was applied more effectively across fields. Rates are increased on thinner areas and reduced on denser crops.
"The greatest variation in crop's biomass is during the first application by the time you get to the third, a lot of the work's been done in evening out the variations. We think average yields have gone up, but I can't quantify that because it was such an odd season last year.
"It will be interesting to see how the N Sensor performs in rape this year, as variable germination means there isn't as much top growth in some places as there is in others," he adds.