Soil scans are reliable, but no miracle solution

Sylvan Nysten, a lecturer/researcher in Sustainable Soil Management at the Aeres University of Applied Sciences in the Dutch city of Dronten, reviewed 5 types of soil scans for the Dutch Experimental Ground for Precision Farming (NPPL).

Sceptical

“I was rather sceptical about some of the maps that these scans provide. So few data that yield so much information? I certainly had my doubts, but they work, are reliable enough and do not fail. The results actually are not bad.”

But he does think that viewing the scans’ ability to map all characteristics at once as some miracle cure is somewhat exaggerated.

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3 of the 5 scanners that were compared last year on a plot of summer barley in the Dutch village of Ens. – Photos: Ruud Ploeg

Possibilities for soil scans

The possibilities that soil scans and the corresponding maps offer for precision farming are quite diverse, Mr Nysten writes in his report ‘Usage of soil scans for Smart Farming’. “Examples are variable fertilising, compost, lime spreading, planting distance etc. It is important that the farmer knows what he wants beforehand, and which soil scan fits this purpose.”

“An EC-map for example, shows the differences in electric conductivity and that the soil differs from place to place. In theory, this can have different causes, but you can be sure that the blue spots on one scan map equal the blue spots on a different part of the plot as far as the soil’s characteristics go.”

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Nysten: “I was rather sceptical about some of the maps these scans provide. The results actually are not bad.”

Add meaning to the scans

“If you asked a farmer to draw a map of his plot and the soil differences by heart, he will produce something like the scan map. The difference is that you exactly know where those spots are and how big they are if you use a scan. This means that you can add meaning to the scans, together with the information the grower already has. A scan precisely shows the spots the grower already roughly has in his mind. They add precision to what the grower already knows.”

5 scans listed

But how reliable are the scans and the maps they produce? And is every scan suitable for every type of soil? Several NPPL participants and many other farmers asked these questions. The following soil scans were compared to get answers to these questions:

• Bioscope aerial images
• CNH SoilXplorer
• Dualem-21S (LoonwerkGPS)
• Loonstra Passive gamma soil scanner
• Veris MSP3 (Vantage Agrometius)

14-hectare summer barley plot

To test the soil scans’ reliability, they were deployed on a 14-hectare summer barley plot with clay type soils. Only the results of the Loonstra Passive gamma soil scanner, the Dualem-21S and the Veris MSP3 were reviewed, because they were the only scanners that produced concrete organic material and lutum values.

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Measuring the soil’s conductivity (EC) between the discs. Right after the harvest it was too dry for results, so the measurement was repeated later.

Vantage Agrometius did not supply a pH-map from the Veris MSP3, because it is not relevant for clay soil. For the Loonstra and Dualem-21S scanner, pH-maps were supplied though. The Loonstra Passive gamma scan measures gamma radiation from radioactive soil particles in the upper layer of 35 centimetres.

The reliability of the CNH SoilXplorer was not analysed, because it only supplied the spatial variation, but no pH, organic material or lutum maps. The same goes for the Bioscope satellite map.

Comparison with 40 samples

Mr Nysten compared the scan results with the values of 40 composite samples out of 1 square meter of tillage layer (0-25 centimetres) each time. He took the samples in random order, all over the plot. Research laboratory Eurofins determined the lutum, organic material and pH percentages of these 40 samples. “Those 40 samples are the standard we assessed”, says Mr Nysten. “We took the correct Eurofins analysis as a starting point.” The Dualem-21S measures at various depths. If there is a stratification in the soil, this scan shows it.