State Water Resources Research Institute Program

Project ID: 2012IA196B
Title: Dielectric Measurement of Soil Nitrate Concentration
Project Type: Research
Start Date: 3/05/2012
End Date: 2/28/2013
Congressional District: Iowa 004
Focus Categories: Agriculture, Methods, Nitrate Contamination
Keywords: nitrate concentration, dielectric spectoscopy, permittivity, spectral analysis
Principal Investigator: Kaleita, Amy
Federal Funds: $ 13,783
Non-Federal Matching Funds: $ 48,996
Abstract: A fast and reliable method for in situ monitoring of soil nitrate-nitrogen (NO3-N) concentration is vital for understanding and improvement of N management practices focused on reduction of NO3-N losses to ground and surface waters from agricultural systems. Conventional methods for soil or solution NO3-N measurement are destructive, time-consuming, costly, and impractical for large-scale or high-resolution monitoring. Hence, there is a need for development of a relatively cheap and reliable indirect measurement method that can continuously monitor NO3-N dynamic in situ.

During the last several decades, the dielectric response of a medium has been intensively used to characterize its physical or chemical properties. Bulk soil permittivity has been used in environmental monitoring to estimate volumetric water content (VWC) and soil salinity. As a result, several methods and multiple instruments have been developed to measure soil dielectric response at MHz frequency. But very few studies have been conducted to estimate change in soil NO3-N concentration using the dielectric response measured at the same spectrum. Furthermore, most of the commercially available dielectric soil sensors, particularly capacitance type probes, provide a single value for permittivity, which can be adequate to estimate a single soil property. Using dielectric measurements at multiple frequencies can help to estimate several physical and chemical soil properties simultaneously.

We propose to investigate the dielectric footprint of pore water NO3-N content on soil bulk permittivity measured at MHz range, which includes the operating frequency of most dielectric soil probes. Hence the goal of the project will be to evaluate the feasibility to estimate changes in pore water NO3-N concentration at different VWC from the dielectric measurements obtained at multiple frequencies at MHz range using the chemometric analyses.

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