Analysis of Soil FTIR/ATR Spectral Data using Wavelet Analysis to Determine Soil Nitrate Content

Wavelet analysis was applied to soil FTIR/ATR spectral data in order to predict nitrate contents. Two experiments were conducted. One consisted of artificially adding known amounts of nitrate, carbonate, and humic acid. Nitrate concentrations for this experiment varied from 0 to 1000 ppm N03. Results indicated that wavelet analysis was able to decompose the spectra to allow for identification of the nitrate peak from other interfering peaks such as carbonate and humic acid. The volume of the nitrate peak for each sample was correlated to nitrate concentration. Results indicated correlation coefficients in the range of 0.98 to 0.99 with standard errors varying from 11.4 to 24.5 ppm N03. In order to determine the ability of wavelet analysis to distinguish nitrate peaks in actual field conditions with low nitrate concentrations, an experiment involving adding nitrate to Capay clay soil in the field in the presence of interfering compounds such as carbonate and humic acid was conducted. Nitrate concentrations varied from approximately 0 to 130 ppm N03. Results indicated that wavelet analysis was able to distinguish the nitrate peak from adjacent and overlapping peaks due to carbonate and other compounds. R2-values ranged from 0.93 for pooled data to 0.99 for individual experiments with standard errors ranging from 8 to 2 ppm N03, respectively.