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Estimation of clay content in brazilian agricultural soils based on portable x-ray fluorescence data
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Portable X-ray fluorescence analysis (pXRF) has been used worldwide
for rapid and low cost soil chemical characterization. Based on pXRF
data, many soil attributes have been satisfactory estimated (e.g., soil
texture). The mineralogy of tropical soils (Oxisols) is dominated
(mainly) by kaolinite and Fe and Al-oxides (hematite, goethite, and
gibbsite). Thus, a good correlation between clay content and oxide
concentration can be expected. We hypothesized that rapid soil
screening using pXRF to assess the oxide concentration could enable
the estimation of soil clay content in Brazilian Oxisols under different
land uses. One hundred and twenty six surface soil samples (0-20 cm)
collected in different farms in the Triangulo Mineiro and Alto
Paranaíba regions, Minas Gerais State, Brazil, were used in this study.
The soil samples were air-dried and sieved (< 2 mm), and scanned
using a Bruker® S1 Titan LE model (Dual Soil mode) pXRF; samples
were each scanned for 60 s. The clay content was determined via
Bouyoucos hydrometer method. Samples were randomly partitioned
with 70% and 30% of soil samples used for modelling and validation,
respectively. Based on simple linear regression, the clay content was
well correlated to oxide concentration, mainly with (Al2O3 + Fe2O3)
and (Al2O3 + Fe2O3 + TiO2). Using multiple linear regression, the clay
content was well estimated (p<0.01) by the equation (clay = -67.25 +
1.95Al2O3 – 1.76Fe2O3) with R2 and R values of 0.83 and 0.91,
respectively. The data validation resulted a correlation close to a 1:1
line (R2 = 0.83; R = 0.91 and RMSE = 79 g kg-1). Thus, we concluded
that the Al2O3 and Fe2O3 concentrations obtained by pXRF were
useful estimators of clay content for soils in a representative
agricultural area in Brazil.
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LIMA, T. M.de et al. Estimation of clay content in brazilian agricultural soils based on portable x-ray fluorescence data. In: WORLD CONGRESS OF SOIL SCIENCE, 21, 2018, Rio de Janeiro. Proceedings... Viçosa, MG: Sociedade Brasileira de Ciência do Solo, 2018. v. 2, p. 238.