MONITORING NITRATE IN SOILS WITH COATED WIRE ION-SPECIFIC ELECTRODES

The high sensitivity and low per-unit cost of nitrate (NO3-) - sensitive coated wire electrodes (CWEs) makes them attractive alternatives to chemical extraction for NO3- assessment in soils and solutions. We used CWEs in the field to quantify soil NO3- in fresh soil extracts, in a laboratory incubation comparing CWEs with anion exchange membranes and soil extracts, and in the field in fertilized and unfertilized soils. Freshly calibrated electrodes performed well in the field when used to measure NO3- in soil extracts and when installed directly in soils. The output of electrodes placed in situ in soils responded linearly, decreasing as the NO3- contents of soils were increased. Soil-installed electrodes performed better in the laboratory than in the field. When the electrodes were left in soils for long periods (days-to-weeks), we had problems with both their durability and the stability of their response to NO3-. Nitrate-sensitive CWEs will be used to the greatest advantage in controlled settings where their output can be calibrated frequently and their contact with solution ensured.