Three of the five scanners that were compared last year on a plot of summer barley in the Dutch village of Ens.
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 centime- tres. The reliability of the CNH SoilXplorer was not analysed, because it only supplied the spa- tial variation, but no pH, organic material or lu- tum 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
NEED TO KNOW
▶ You need to know what you are looking for, otherwise a scan is pointless
▶ A scan precisely shows the spots that the grower already roughly has in his mind
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Mr Nysten. “We took the correct Eurofins analy- sis as a starting point.” The Dualem-21S meas- ures at various depths. If there is a stratification in the soil, this scan shows it.
The conclusions The main question of this test was: which soil scan provides the most reliable and useful in- formation for precision farming? The compari- son between the scan maps of the Loonstra, the Geonics and the Veris scanners showed that the reliability is fine for pH, lutum and or- ganic material. “But”, adds Mr Nysten, “the add- ed value of the soil scans on this type of clayish soil is limited. They do not show more than a composite sample would because the soil of the test plot is quite homogenous. You could add that this is no news for the grower. On the other hand, you can now say that the plot is de- monstrably homogenous. That is a benefit too.” This is certainly true for growers who start working on new plots or in situations with rap- idly changing rental plots. Both are common, due to scaling-up in arable farming and spe- cialisation in intensive cultivation. As demon- strated by the graphs of the scans with the ref- erence samples, the small spatial variation is difficult to map with these scans. The R2 (coef- ficient of determination) is quite low, except
▶ FUTURE FARMING | 24 May 2019
About the comparison
Five soil scans were reviewed in the com- parison and they were compared to 40 samples taken manually. Prices men- tioned are relevant in The Netherlands.
Bioscope aerial images
• The soil zone map is an aerial image (sat- ellite, drone) or Bioscope and shows the various soil zones within a plot. Just like the other techniques, it needs soil sam- ples to determine values for soil charac- teristics. The grower can use it as a rela- tive map to make an estimate of the soil variation, to act on that and to explain differences in crop growth and growth potential.
• Costs: The Bioscope soil zone map is part of the Bioscope seasonal subscrip- tion of € 250 per company (maximum of 50 hectares)
PHOTO: RUUD PLOEG
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