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Wavelength Identification for Reflectance Estimation of Surface and Subsurface Soil Properties

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2007 ASAE Annual Meeting  071046.(doi:10.13031/2013.22894)
Authors:   Kyou Seung Lee, Dong Hoon Lee, Kenneth A Sudduth, Sun Ok Chung, Scott T Drummond
Keywords:   Precision Agriculture, Soil Sensors, Soil Property, Reflectance

Optical diffuse reflectance sensing is a potential approach for rapid and reliable on-site estimation of soil properties. In this study, reflectance sensing in visible (VIS) and near-infrared (NIR) wavelengths was combined with partial least squares (PLS) regression to estimate surface and subsurface soil properties, and wavelength bands important for estimating soil properties were identified. Soil cores (120 cm deep) from ten fields in five states in the US cornbelt were segmented by horizon and analyzed in laboratory for texture (sand, silt, and clay fractions), cation exchange capacity (CEC), Ca, Mg, K, pH, total and organic C, and total N. Using air-dried, sieved soil samples, reflectance data were obtained from 350 to 2500 nm with a laboratory spectrometer. Over all soil horizons, cross-validated predictions of organic C were good (R2=0.87, RPD (the ratio of standard deviation to standard error of prediction) =2.78), while predictions of clay fraction, CEC, and pH were also acceptable (0.63< R2<0.79, RPD about 2). Calibrations restricted to the surface horizon were somewhat better, with R2 values from 0.81 to 0.85 and RPD values from 2.08 to 2.73 for clay fraction, Ca, CEC, and organic C. Important wavelengths were 440-600 nm and 1780-2460 nm for clay; 470-600, 965, and 1750-2330 nm for CEC; and 450-465, 965, 1409, and 1775-2200 nm for organic C. These results will be useful in the design and application of in-situ close range sensors for soil physical and chemical properties.

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