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Mogens Humlekrog Greve

Visible-Near-Infrared Spectroscopy Prediction of Soil Characteristics as Affected by Soil-Water Content

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Soil physical characteristics are important drivers for soil functions and productivity.
Field applications of near-infrared spectroscopy (NIRS) are already
deployed for in situ mapping of soil characteristics and therefore, fast and
precise in situ measurements of the basic soil physical characteristics are
needed at any given water content. Visible-near-infrared spectroscopy (vis–
NIRS) is a fast, low-cost technology for determination of basic soil properties.
However, the predictive ability of vis–NIRS may be affected by soil-water
content. This study was conducted to quantify the effects of six different
soil-water contents (full saturation, pF 1, pF 1.5, pF 2.5, pF 3, and air-dry)
on the vis–NIRS predictions of six soil physical properties: clay, silt, sand,
water content at pF 3, organic carbon (OC), and the clay/OC ratio. The effect
of soil-water content on the vis–NIR spectra was also assessed. Seventy soil
samples were collected from five sites in Denmark and Germany with clay
and OC contents ranging from 0.116 to 0.459 and 0.009 to 0.024 kg kg-1,
respectively. The soil rings were saturated and successively drained/dried
to obtain different soil–water potentials at which they were measured with
vis–NIRS. Partial least squares regression (PLSR) with leave-one-out crossvalidation
was used for estimating the soil properties using vis–NIR spectra.
Results showed that the effects of water on vis–NIR spectra were dependent
on the soil–water retention characteristics. Contents of clay, silt, and sand,
and the water content at pF 3 were well predicted at the different soil moisture
levels. Predictions of OC and the clay/OC ratio were good at air-dry soil
condition, but markedly weaker in wet soils, especially at saturation, at pF 1
and pF 1.5. The results suggest that in situ measurements of spectroscopy are
precise when soil-water content is below field capacity.
TidsskriftSoil Science Society of America Journal
Sider (fra-til)1333-1346
Antal sider14
StatusUdgivet - 2018

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