|Kim, H - NATL INST OF AG ENG KOREA|
|Hummel, J - ARS RETIRED|
|Motavalli, P - UNIVERSITY OF MISSOURI|
Submitted to: Asian Conference on Precision Agriculture
Publication Type: Proceedings
Publication Acceptance Date: June 29, 2007
Publication Date: August 2, 2007
Citation: Kim, H.J., Hummel, J.W., Sudduth, K.A., Motavalli, P.P. 2007. Ion-selective electrodes for simultaneous analysis of soil macronutrients. In: Proceedings 2nd Asian Conference on Precision Agriculture. August 2-4, 2007, Pyeongtaek, Korea. 2007 CDROM. Technical Abstract: Automated sensing of soil macronutrients would be useful in mapping soil nutrient variability for variable-rate nutrient management. Ion-selective electrodes (ISEs) are a promising approach because of their small size, rapid response, and ability to directly measure the analyte. This study reports on the laboratory evaluation of a sensor array including three different ISEs, based on TDDA-NPOE and valinomycin-DOS membranes, and cobalt rod, for the simultaneous determination of nitrate-nitrogen, available potassium, and available phosphorus in soil extracts. Thirty-seven Illinois and Missouri soils were extracted using the Kelowna soil extractant (0.25M CH3COOH + 0.015M NH4F). The response of each electrode type in mixed solutions of nitrate, potassium and phosphate ions was modeled based on the Nikolskii-Eisenman equation with all coefficients of determination (r2)greater than or less than 0.95 (P less than 0.001). In soil extracts, the nitrate ISEs provided concentrations similar to those obtained with standard laboratory methods (r2 = 0.89, P less than 0.001). Concentrations obtained with the K ISEs were about 50% lower than those obtained with standard methods due to lower K extraction by the Kelowna solution (r2 = 0.85, P less than 0.001). The P ISEs provided concentrations about 64% lower than those obtained with standard methods due to a combination of decreased P estimates in soil extracts and lower P extraction by the Kelowna solution; however, there was a strong linear relationship (r2 = 0.81, P less than 0.001). Although P and K concentrations were low in comparison to standard laboratory procedures, a calibration factor could address this issue. These results show that ion-selective electrode technology can be implemented successfully for nitrate-nitrogen, available potassium, and available phosphorus measurement with the Kelowna extractant.