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Application of Ion-Selective Electrodes for Simultaneous Analysis of Soil Macronutrients
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: 2007 ASAE Annual Meeting 071004.
Authors: Hak-Jin Kim, Kenneth A Sudduth, John W Hummel, Scott T Drummond
Keywords: ion-selective electrodes, soil nutrients, precision agriculture, sensors, soil testing
Automated sensing of soil macronutrients would be useful in mapping soil nutrient variability for variable-rate nutrient management. This study reports on the evaluation of a sensor array composed of three different ion selective electrodes (ISEs), in conjunction with the Kelowna soil extractant, for the simultaneous determination of soil N, P, and K. Data were obtained for two sets of soils – single samples from 37 fields across Illinois and Missouri (MO-IL) and 36 samples from a single Illinois research field (NIARC). The response of each ISE type in mixed solutions of N, P, and K ions was modeled based on the transformed Nikolskii-Eisenman equation with all coefficients of determination (r2) = 0.95. The nitrate ISEs provided concentrations similar to those obtained with standard methods (r2 = 0.89). The soil ISE-K concentrations were about 47% lower than those by standard methods due to lower K extraction efficiencies by Kelowna solution. The combination of lower P estimates in soil extracts and reduced P extraction efficiencies by Kelowna provided 63% lower ISE values as compared to standard methods. However, there were strong relationships between ISE and standard methods for K and P concentrations (r2 > 0.80). The applicability of models based on the MO-IL dataset to new ion-selective membranes in the NIARC test was limited by high bias errors, perhaps due to the use of a 2-point normalization method that could not effectively compensate for sensitivity differences between membranes. Additional research will be required to develop calibration methods that can provide more accurate results across different membranes.