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Simultaneous Analysis of Soil Macronutrients Using Ion-Selective Electrodes

^a National Institute of Agricultural Engineering (NIAE), Suwon, South Korea 441-100
^b USDA-ARS Cropping Systems and Water Quality Research Unit, Columbia, MO 65211
^c Dep. of Soil Environmental and Atmospheric Sciences, Univ. of Missouri, Columbia, MO 65211

View larger version (12K): [in this window] [in a new window]   Fig. 1. Functional diagram of the automated test stand for ion-selective electrodes (ISEs).

View larger version (11K): [in this window] [in a new window]   Fig. 2. Schematic diagram for two-point normalization; EMF = electromotive force.

View larger version (28K): [in this window] [in a new window]   Fig. 3. Experimental data and response surfaces of (a) N, (b) P, and (c) K electrodes to mixtures of ions at varying concentrations; EMF = electromotive force.

View larger version (9K): [in this window] [in a new window]   Fig. 4. Effects of (a) P and NO3–N ions on N ion-selective electrode (ISE) response, (b) NO3–N and P ions on P ISE response, and (c) P and K ions on K ISE response; EMF = electromotive force. The standard deviation bars indicate EMF variation across three replications and five electrodes of the same type (n = 15).

View larger version (9K): [in this window] [in a new window]   Fig. 5. Relationships between validation sample (a) NO3–N, (b) P, and (c) K determined by ion-selective electrode (ISE) and by standard instruments, i.e., automated ion analyzer (Lachat) for N and inductively coupled Ar plasma (ICP) spectrometer for P and K. Data are presented as mean and standard deviation; however, regression equations and statistics were calculated using individual data points.

View larger version (10K): [in this window] [in a new window]   Fig. 6. Relationships between soil extract (a) NO3–N, (b) P, and (c) K determined by ion-selective electrode (ISE) and by standard instruments, i.e., automated ion analyzer (Lachat) for N and inductively coupled Ar plasma (ICP) spectrometer for P and K. Data are presented as mean and standard deviation; however, regression equations and statistics were calculated using individual data points.

View larger version (11K): [in this window] [in a new window]   Fig. 7. Relationships between soil (a) NO3–N, (b) P, and (c) K extracted with Kelowna and with standard extractants, i.e., 1 mol L–1 KCl for N and Mehlich III for P and K extraction, using an automated ion analyzer (Lachat) for N and inductively coupled Ar plasma (ICP) spectrometer for P and K.

View larger version (10K): [in this window] [in a new window]   Fig. 8. Relationships between soil (a) NO3–N, (b) P, and (c) K determined by Kelowna solution and ion-selective electrodes (ISEs), and by standard extractants and an automated ion analyzer (Lachat) for N and inductively coupled Ar plasma (ICP) spectrometer for P and K. Data are presented as mean and standard deviation; however, regression equations and statistics were calculated using individual data points.