Development of Field Mobile Soil Nitrate Sensor Technology to Facilitate Precision Fertilizer Management.

The Late Spring Nitrate Test (LSNT), also known as the pre-sidedress nitrate test (PSNT), is an established tool for N fertility management in corn production. Although shown to be effective for improving NUE and reducing NO₃^- leaching losses, the LSNT is not widely used by farmers, because of its cost, low spatial resolution, and the time delay between soil sampling and the availability of a N fertilizer prescription increases risk for farmers.  The overall goal of our research is to develop soil NO₃^- sensor technology that can be attached to farm implements and used to determine in-real-time on-the-go soil NO₃^- concentrations with sufficient accuracy to facilitate precision application of nitrogen fertilizers. We used diamond-attenuated total internal reflectance (D-ATR) Fourier Transform Infrared (FTIR) spectroscopy as the basis for the soil NO₃^- sensor system.  We were successful in developing methodology for collecting soil spectra with an Agilent 4100 Exoscan FTIR Spectrometer from 5 soil types amended with different quantities of KNO₃ and processing collected data using partial least squares regression analysis. Cross validation r² (predicted vs. actual NO₃^-  concentrations) for pooled data was 0.73, suggesting great potential of utilizing the Exoscan FTIR Spectrometer for soil NO₃^-  determination. Currently we are analyzing spectra of the soil samples collected from four agricultural fields to encompass variation in soil characteristics.