@article{fdi:010061426,
  title = {{B}est practices for obtaining and processing field visible and near infrared ({VNIR}) spectra of topsoils},
  author = {{G}ras, {J}. {P}. and {B}arth{\`e}s, {B}ernard and {M}ahaut, {B}. and {T}rupin, {S}.},
  editor = {},
  language = {{ENG}},
  abstract = {{D}iffuse infrared reflectance spectroscopy is considered a promising approach for addressing soil quality, and its use directly in the field might be an achievable challenge. {T}he present work aimed at optimizing the acquisition procedure of visible and near infrared reflectance ({VNIR}) spectra of topsoils (0-20 cm) in the field, in order to predict usual soil properties. {T}he studied set included 201 samples originating from six fields in different regions of large-scale crop cultivation in {F}rance. {S}pectra were acquired using a portable spectrophotometer. {S}pectrum acquisition procedures included scanning on the soil surface, on raw or smoothed (cut) cores collected using an auger, and on clods resulting from core crumbling. {I}n addition, spectra were also acquired on air-dried clods, either 2-mm sieved or not (laboratory conditions). {F}urthermore, 42 mathematic pretreatments were compared (including derivatives, standard normal variate {SNV}, multiplicative scatter correction {MSC}, etc.). {I}dentifying the most appropriate scanning and pretreatment procedures was done through four-group cross-validation. {U}sing the most appropriate pretreatment calcium carbonate content was very well predicted whatever the scanning procedure used ({RPD} = 6.9-9.1; {RPD} is the ratio of standard deviation to standard error of crossvalidation; for soil properties {RPD} > 2 denotes accurate predictions); good predictions were achieved for total nitrogen ({RPD} =2.5-3.0), organic matter ({RPD} = 2.1-2.8) and exchangeable potassium ({RPD} = 2.9-3.2); but available phosphorus was poorly predicted ({RPD} = 1.6-1.8). {E}xcept for available phosphorus, accurate predictions of these properties could therefore be achieved whatever the scanning procedure used, thus in the field. {B}est predictions were often obtained using spectra acquired on 2-mm sieved air-dried samples (i.e. in laboratory conditions), otherwise using spectra acquired on raw cores. {A}cquiring spectra on cores, on raw cores especially, was the most appropriate field procedure; it led to predictions comparably accurate to those achieved in the laboratory with 2-mm sieved air-dried samples. {S}imilar prediction accuracy for field and laboratory {VNIRS} is counterintuitive due to variable field conditions (moisture, temperature, stoniness, etc.). {I}t might result from higher number of replicates in the field than in the laboratory (often inherent to field vs. lab conditions) and/or higher sample density and cohesion, which would improve reflectance signal. {F}or spectra acquired on cores, best calibrations were achieved with {MSC} and first derivatives for calcium carbonate, total nitrogen and organic matter, but without pretreatment for exchangeable potassium and available phosphorus. {S}econd derivatives always yielded poor results.},
  keywords = {{S}oil organic matter ; {N}utrients ; {C}alcium carbonate ; {V}isible and near infrared reflectance spectroscopy ({VNIRS}) ; {P}roximal soil sensing ; {FRANCE}},
  booktitle = {},
  journal = {{G}eoderma},
  volume = {214},
  numero = {},
  pages = {126--134},
  ISSN = {0016-7061},
  year = {2014},
  DOI = {10.1016/j.geoderma.2013.09.021},
  URL = {https://www.documentation.ird.fr/hor/fdi:010061426},
}