Electro-magnetic fields give detailed soil maps

27 August 1999

Electro-magnetic fields give detailed soil maps

By Charles Abel

PRECISION farming has a new tool to aid variable crop management – the Solutech Magna-Scan – which can produce detailed soil maps based on up to 100 measurements a hectare (40/acre) for just £17.30/ha (£7/acre).

Soil type is the driving factor behind most crop variation, so measuring it accurately is a key to successful precision farming, says Justin Smith of Solutech, based at Shuttleworth, Beds.

The MagnaScan, developed at a cost of £80,000 uses an electromagnetic field to detect changes in the clay and water content of soil to a depth of 1-1.5m (3-5ft). Used behind an ATV quad-bike travelling at up to 20mph, readings can be taken as often as once a second. For farm studies readings are taken at tramline widths and every 20-24m to provide 60-100 readings a hectare (24-40/acre).

A GPS signal is used to pinpoint the location of each reading which is held in an on-board data logger ready for conversion into a soil map.

With each reading covering about 0.3t of soil to a depth of 1m that means over 20t is tested a hectare (8t/acre). That compares with just 0.5kg/ha (7oz/acre) to 15cm (6in) using core sampling on a conventional 1ha (2.4-acre) grid.

The extra data also means maps are more accurate. Less fudging is needed from the smoothing software than when just one reading is taken for each hectare. "You can almost get a picture of what is happening from the raw data alone."

Indeed, results to date are comparable with the more costly 100m grid mapping offered by the Soil Survey, says Mr Smith.

Main agent Dalgety is now offering a national service, costing £17.30/ha (£7/acre) for scanning, hard copy map and data disk. Over 1200ha (3000 acres) is already booked for September.

Several other distributors have already shown an interest, says Mr Smith. "Now that seed and chemical margins are so tight they are very keen to extend their agronomy package, so starting with the soil and matching input to it makes sense."

Indeed the real value of MagnaScan lies in its interpretation, says Mr Smith. "It is more than just sampling. It has to be driven by agronomy and we will only be offering it through agents who can provide that support.

Using site knowledge MagnaScan data can be used to identify soil compaction, water-logging and drains and areas for variable irrigation, cultivations, sowing rates and input use.

Over 1000ha (2500 acres) were mapped during development, including work for Birds Eye. "They were interested in the effect of soil type on maturity and the potential to vary variety and sowing date to get more even maturity," says Mr Smith.

The detailed map will also help target specific soil tests, including pH, P, K, Mg. "All those are linked to soil type, so if you know where the soil varies, you can target your sampling more accurately and match recommendations to areas of similar soil."

Knowing how soil type varies could also help make more of nutrient test results. "At the moment P and K rates are adjusted as indices vary across a field. But differences in application rate between indices are relatively small.

"What really counts is the combination of index and soil type. For a 10t/ha crop where straw has been removed an index 2 could mean applying 120kg/ha of K20 on a sandy soil or 260kg/ha on a clay soil. That is much more of a difference than between index 1 and 2 on the same soil and certainly a lot more than between index 2- and 2+." &#42


&#8226 Maps soil type.

&#8226 Operates at 20mph.

&#8226 Uses 60-100 readings a hectare.

&#8226 Costs £17.30/ha.

&#8226 Good guide to yield.

&#8226 Helps target sampling for pH, P, K, Mg.

&#8226 Dalgety national service.

Trials sites

Sampling every 2m has identified significant variations in supposedly uniform trials sites, says Justin Smith. Differences in soil depth and type, sub-soil type and even a gas main have been identified within trial plots, he says. "Those factors could have a big effect on results." MagnaScan means variations can now be taken into account when trials are planned, he says. NIAB, Nickerson and Advanta Seeds and Dalgety are using the system, but at least one other organisation has decided not to, he says.

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