The Relation between Soil Water Repellency and Water Content can be Predicted by Vis–NIR Spectroscopy

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Soils can be water repellent, when covered by hydrophobic organic matter. There are several
consequences of soil water repellency (SWR), such as decreased crop yield, erosion and increased
risk of ground watercontamination. The severity of SWR varies non-linearly with water content (w),
and it is extremely laborious to obtain complete SWR-w curves. We combined a three-parameter
moisture-dependent SWR (MD-SWR) model with visible near-infrared (vis–NIR) spectroscopy as a
fast and novel method to estimate the SWR-wcurve. The method was applied to a data set of 71 soil
samples, representing five dominant soil orders of the South Island of New Zealand (OC: 0.021 –
0.147 kg kg-1, clay: 0.000 – 0.520 kg kg-1). The degree of SWR was measured at air-dry conditions
(SWRAD), and at several water contents above air-dried conditions, obtained by adding water in small
increments until the water content at which the soils became wettable (wNON) was reached. The threeparameter
MD-SWR model was fitted to the measured SWR-w curves between the water content at
air-dry conditions (wAD) and wNON. Then, the total SWR was derived as the trapezoidal integrated
area underneath the SWR-w curves (SWRAREA). Air-dried soil samples were scanned with a vis–NIR
spectrometer (DS2500 spectrometer, Foss, Denmark) in the 400 – 2500 nm range. Each of the three
MD-SWR model parameters was correlated to vis–NIR spectra with partial least squares regression
and ten-fold cross validation (R2 between 0.56 and 0.71). Next, the predicted model parameter values
were used to obtain vis–NIR predicted SWR-w curves between wAD and wNON, and SWRAREA was
derived from these curves. Results show that vis–NIR can predict the shape of the SWR-w curves as
well as SWRAREA (R2 = 0.56) across a highly variable dataset from a single vis–NIR scanning and
one SWR measurement at air-dried conditions.
Original languageEnglish
Publication year2019
Publication statusPublished - 2019
Event2018 - 2019 SSSA International Soils Meeting : SOILS ACROSS LATITUDES - Sheraton San Diego Hotel & Marina, San Diego, United States
Duration: 6 Jan 20199 Jan 2019


Conference2018 - 2019 SSSA International Soils Meeting
Location Sheraton San Diego Hotel & Marina
CountryUnited States
CitySan Diego
Internet address

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