NIR gets its hands dirty

Generally, animal manure is a more environmentally-friendly way to supply crops with nutrients than synthetic fertilizers, but it is not without its problems. For animal manure can contain various contaminants that cause problems if they escape from fields into nearby bodies of water.

One such contaminant is the powerful steroid 17β-estradiol, which can cause male fish to become female and cause reproductive disorders in humans. So farmers need to ensure they don't apply too much animal manure to their fields. But how much is too much can vary field by field, depending on the physical properties of the soil and how strongly the 17β-estradiol binds to the soil particles, known as the sorption coefficient.

Working out a soil's physcial properties, including its 17β-estradiol sorption coefficient, has traditionally been a time-consuming business involving lots of laboratory experiments. Now, however, a team of Canadian soil scientists led by Annemieke Farenhorst at the University of Manitoba has shown that NIR spectroscopy offers a much faster and more convenient alternative.

Using conventional techniques, they analysed over 600 soil samples taken from fields in Manitoba and Saskatchewan in Canada in order to determine their carbon content, soil pH, soil texture and 17β-estradiol sorption coefficient. Then, they analysed the soil samples using NIR spectroscopy and found that the resultant spectral data were strongly correlated with the samples' carbon content, soil pH and 17β-estradiol sorption coefficient.

As they report in a paper in the Journal of Agricultural and Food Chemistry, this shows that NIR spectroscopy can produce accurate values for these three soil properties, although it was far less successful at determining soil texture. The recent development of portable NIR spectrometers should now allow farmers to perform these kinds of soil analyses directly in their fields, says Farenhorst.

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