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This article in SSSAJ

  1. Vol. 76 No. 5, p. 1536-1547
     
    Received: Nov 14, 2011
    Published: September 12, 2012


    * Corresponding author(s): chige@iastate.edu
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doi:10.2136/sssaj2011.0391

Estimating Soil Solution Nitrate Concentration from Dielectric Spectra Using Partial Least Squares Analysis

  1. Giorgi Chighladze *a,
  2. Amy Kaleitaa,
  3. Stuart Birrella and
  4. Sally Logsdonb
  1. a Dep. of Agricultural and Biosystems Engineering, Iowa State Univ. 100 Davidson Hall, Ames, IA 50011
    b USDA, National Lab. for Agriculture and the Environment, 2110 University Boulevard, Ames, IA 50011-3120

Abstract

Fast and reliable methods for in situ monitoring of soil NO3–N concentration could help guide efforts to reduce NO3–N losses to ground and surface waters from agricultural systems. While several studies have been done to indirectly estimate NO3–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 NO3–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 KNO3 and KCl were analyzed using a partial least squares (PLS) regression method. Global models could not estimate NO3–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 NO3–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 m3 m−3.

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Copyright © 2012. Copyright © by the Soil Science Society of America, Inc.