Field-scale spatial correlation between soil and Vis-NIR spectra in the Cerrado biome of Central Brazil

International audienceVisible and near-infrared (Vis-NIR) spectroscopy is a tool to determine soi l spatial variability and has been used to map soils and their properties. Considering that physical , chemical , mineralogical , and morphological soi l properties can affect the intensity and the depth of the spectral reflectance band in the Vis-NIR region, the objectives of this work were to: (i) evaluate the potential of the reflectance inflection difference (RID) to discriminate soils; and (ii) veri f y potential spatial correlations of the RID with soi l properties, compared with the f u l l spectra, in order to build thematic maps at a fiel d scale. In a farm of 375 ha, 78 soil samples from the 0.87-0.92-m depth were collected in a regular grid of 200 m, with a focus on the soi l diagnostic horizon (Bw horizon). The sampled soils were a Latossolo Vermelho-Amarelo & PRIME;acrico (Haplic Ferralsol) and a Latossolo Ver-melho distr & PRIME;ofico (Rhodic Ferralsol). Twenty-two physical , chemical , mineralogical , and morphological soi l properties were determined, and the Vis-NIR spectra between 400 and 2500 nm were measured. Considering the presence of an inflection band and its relationship with soi l properties, the spectral bands used to calculate the RID were between (base 1/base 2): 400-510, 730-930, 1290-1450, 1800-1950, 2000-2218, and 2218-2290 nm. The RID failed to map the spatial variability of soi l properties, with a Kappa inde x of 39%; therefore, it is not a good parameter for building thematic maps of soi l parameters. In addition, the complete spectru m (mainly in 400-510, 730-930, 1290-1450, 1800-1950, 2000-2218, and 2218-2290 nm) was better spatially correlated with soi l properties than the decomposition of the spectrum by the RID. Soi l classification and level of dis-cretization as affected by spectral variability were also discussed here. Three soi l groups were discriminated mainly by the Ki and K r indexes and clay content. Moreover, the variability of the spectra was conditioned by the spatial variability of the mentioned variables. The clay content for soils with a discrepant particle size (group 1 compared with groups 2 and 3) and the Ki and K r indexes for soils with a homogeneous particle size (between groups 2 and 3), associated with the f u l l Vis-NIR spectral analysis, allowed building thematic maps with a good precision, without the need of mathematical models; this was possible by the modification of the reflectance intensity and the size of the concavity of the spectral band