19 November 1999

Precision farming advance

A TRACTOR-mounted sensor that measures the nitrogen requirements of a growing crop and automatically adjusts the output of the fertiliser spreader to match it is the latest addition to the precision farming armoury.

Developed and marketed by Lincs-based Hydro Agri Precise, it uses a flat plastic bar (looking not unlike a racing car spoiler) on the roof of the tractor to do the work. At each end of the bar are downward-facing sensors which measure how green and dense of crop underneath is, while facing upwards is a light intensity sensor that checks the level of ambient light.

Since greenness is a measure of the amount of chlorophyll in the leaves and hence of plant health, the readings can be translated into a nitrogen requirement figure in kg/ha. That can then be passed down the wires (via a black box or two) to the fertiliser spreaders output-varying mechanism which can then put on more fertiliser where its needed and less where it isnt.

You can use it as part of a GPS system if you want maps, or on its own with the spreader if you dont.

The sensing mechanism may be relatively simple, but it has taken nearly five years and a hundred separate trials across Europe to produce the data that allows the sensor readings to be turned into truly accurate nitrogen requirement figures, says managing director Tony Robinson. Last year it was trialled on 35,000ha (86,000 acres).

In the field, the operator must calibrate the system for each field first by taking greenness readings from a small area of crop with a hand-held meter, then using a chart (or ringing Hydro) to get the correct figure for that particular crop variety.

Once underway, the actual quantity of fertiliser being applied can go up or down by 30% in any one spot – even in a field where the crop looks totally uniform. However, usage over the whole field is likely to be the same as if it was spread uniformly. There is also an override function for use in places where crop health is due to compaction or disease rather than lack of N.

And the benefits? In almost all cases a 2% increase in yield should be possible, says Mr Robinson, which currently equates to a 10% rise in profit. Plus higher proteins and less lodging thanks to the ultra-accurate application. Its not suitable for everyone; if you are lucky enough to have exactly the same soil type across the farm, it wont help much. In fact, the more variable your soils, the more you stand to gain.

The unit is compatible with all fertiliser spreaders (and controllers) on the market. Though currently designed for cereals, the N sensor should soon be usable on rape, potatoes and sugar beet.

Cost is £10,000 if you buy it or £4500 to rent it for a year and the company says it should be suitable for anyone with more than 500ha (1200 acres) of cereals. It expects to sell 100 units this year and is now looking at the possibility of using the same system with sprayers. &#42