UC Merced

Inorganic nitrogen from chemical fertilizer and livestock waste is a major source of pollution in groundwater, surface water and the air. Commercially available in situ chemical sensors (ion selective electrodes) and physical sensors (soil temperature, moisture and EC) have been considered a potential tool for measuring and monitoring nitrate (N03 -) and ammonium (NH4l in agricultural soils irrigated with dairy waste water. We found physical sensor performance to be satisfactory (with the exception of soil moisture "smart" sensors) but found that ISEs experience a suite of technical problems including interfering ions, calibration drift and temperature dependence. Through non-ideal field deployments and controlled laboratory testing, we developed a temperature correction scheme using multivariable regression to compensate for temperature ranges experienced in the field (10°C to 30°C). Our efforts to independently validate ISE response with ion chromatography were inconclusive. Results are presented in the context of deployment techniques (in situ versus soil lysimeters), calibration error, and temperature compensation. In general, there are many issues that currently inhibit the success of ISEs in our field tests and time intensive calibrations required to create accurate temperature corrections are prohibitive to their immediate success in environmental monitoring.