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Near-Infrared Reflectance Spectroscopy–Principal Components Regression Analyses of Soil Properties

^a Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
^b USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011
^c USDA-NRCS, Soil Survey and Resource Assessment, P.O. Box 2890, 14th Independence Ave. S.W., Washington, DC 20250
^d Jr., Dep. of Agricultural & Biosystems Engineering, Iowa State Univ., Ames, IA 50011

View larger version (24K): [in a new window]   Fig. 1. Summary of the near-infrared reflectance spectroscopy–principal components regression (NIRS–PCR) technique. RMSECV is root mean standard error of cross validation

View larger version (28K): [in a new window]   Fig. 2. The average near-infrared spectra for soils containing low moisture content (<0.01 kg kg-1) from four Major Land Resource Area (MLRA) groups. The total C (g kg-1) and total N (g kg-1) of these samples are as follows: MLRA 9, total C = 14.5, total N = 1.3; MLRA 67, total C = 7.9, total N = 0.9; MLRA 77, total C = 4.5, total N = 0.6; MLRA 105, total C = 17.3, total N = 1.6

View larger version (49K): [in a new window]   Fig. 3. Distribution of the first three principal components (PC1, PC2, and PC3) for soils from four Major Land Resource Areas (MLRAs). The PCs are based on the first derivatives of the optical density [log(1/R)] from 1300 to 2500 nm

View larger version (41K): [in a new window]   Fig. 4. The influence of wavelength on the correlation between reflectance intensity, log(1/R), and values of some soil properties. Dotted lines are lines of zero correlation and are separated by ±1 from each other

View larger version (79K): [in a new window]   Fig. 5. Relationship between soil properties measured by standard laboratory procedures and predicted by NIRS–PCR technique. The 1:1 line is indicated on each figure. MLRA is Major Land Resource Area