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Estimating Soil Solution Nitrate Concentration from Dielectric Spectra Using Partial Least Squares Analysis
Author(s) -
Chighladze Giorgi,
Kaleita Amy,
Birrell Stuart,
Logsdon Sally
Publication year - 2012
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2011.0391
Subject(s) - partial least squares regression , mean squared error , soil science , water content , least squares function approximation , mathematics , analytical chemistry (journal) , nitrate , environmental science , chemistry , statistics , environmental chemistry , geology , geotechnical engineering , organic chemistry , estimator
Fast and reliable methods for in situ monitoring of soil NO 3 –N concentration could help guide efforts to reduce NO 3 –N losses to ground and surface waters from agricultural systems. While several studies have been done to indirectly estimate NO 3 –N concentrations from time domain spectra, no research has been conducted using a frequency domain technique. Hence, the goal of this laboratory study was to estimate NO 3 –N concentrations from frequency‐response data obtained in a frequency range of 5 Hz to 13 MHz. Dielectric spectra of soil samples wetted to five different volumetric water contents (VWC) with 24 solutions containing different concentrations of KNO 3 and KCl were analyzed using a partial least squares (PLS) regression method. Global models could not estimate NO 3 –N concentrations with sufficient accuracy. Models based on the imaginary part of the permittivity were better than those based on the real part. The PLS model estimates were improved when low VWC data and high Cl − concentration were eliminated, reducing the RMSE for NO 3 –N from 57 to 28 mg L −1 . The best results were obtained when the PLS models were constructed at fixed VWC levels using the data without high Cl − concentration. The performance of these models improved with increasing VWC level, reaching the lowest RMSE of 18 mg L −1 at VWC of 0.30 m 3 m −3 .