Evaluation of a Solid-State Electrode for the Rapid Detection of Soil Nitrate-Nitrogen

In recent years, the prolific usage of nitrogenous fertilizers in the agricultural area of China has resulted in inefficient nitrogen usage, environmental pollution and the degradation of the soil fertility. As such, a rapid, low-cost and reliable soil detection method is urgently needed. This study reported on the laboratory evaluation of a solid-state ion-selective electrode, based on a nitrate doped polypyrrole polymer (PPy(NO3-)), for the simultaneous detection of soil nitrate-nitrogen. The potentiometric slope of these PPy(NO3-) electrodes for nitrate was found to be -(53.3 +/- 0.8) mV/decade over a linear range of three decades of concentration 10(-4)similar to 10(-1) mol/L. It was also found that these electrodes had a nitrate detection limit of 5.0 x 10(5) mol/L. Impacts of soil extractant conditions were also tested. The electrodes displayed better performances for nitrate solutions with pH lower than 7.0. The potentiometric responses of electrodes exhibited a negative drift tendency of 0.6 mV/degrees C, which was probably caused by changes of the polymer morphology and the solution ionic activity. In order to reduce the interferences of coexisting anion, deionized water was chosen as soil extractant. It is shown that a fast determination of soil nitrate levels for site-specific control of fertilizer application could be realized using the PPy(NO3-) electrodes together with an automatic fluidic control system.