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Soil Reflectance Sensing for Determining Soil Properties in Precision Agriculture

Thomasson, J.A., Sui, R., Cox, M.S., Al-Rajehy, A.
Transactions of the ASAE 2001 v.44 no.6 pp. 1445-1453
calcium, clay, magnesium, nutrient content, pH, precision agriculture, reflectance, soil nutrients, soil sampling, soil texture, texture, Mississippi
Soil samples were collected on a 0.4-ha (1.0-ac) grid from two agricultural fields in northeastern Mississippi. The samples were measured for soil nutrient composition, soil texture, and diffuse reflectance between 250 and 2500 nm. The data were examined for two purposes: (1) to understand the relationships between soil properties and reflectance spectra, and (2) to understand the sources of variability in the reflectance spectra. From the raw reflectance spectra, 50-nm-band averages were calculated. There were significant correlations between groups of the averaged spectra and soil properties, but no single 50-nm band was highly correlated to any soil property. Soil nutrients were better correlated with spectra in one field, but texture was better correlated with spectra in the other. Only Ca and Mg in one field and clay and pH in the other had multiple-regressor model correlations with R 2 values greater than 0.50. The relationships between soil properties and reflectance spectra were not consistent between fields. Based on the study of variability in reflectance spectra, the results of which were significantly dependent on the instrument used in this study, it was found that certain sections of the spectrum are more useful for discriminating among soil samples with differing characteristics. Spectral regions of high discriminatory power were 400 to 800 nm and 950 to 1500 nm.