Estimation of phosphorus and potassium as nutrient components in soil using magnetic-field-assisted laser-induced breakdown spectroscopy.

Estimating soil nutrient components is a key analytical methodology for creating fertilization maps for agricultural fields. To develop a compact laser-induced breakdown spectroscopy (LIBS) system for fertilizer map creation, this study examined the sensitivity enhancement of phosphorus (P) and potassium (K) in soil by adding magnetic field assistance using Halbach-arrayed neodymium magnets. The LIBS signal intensity was compared with the plant-available content determined by chemical analysis. The addition of a magnetic field (~ 0.5 T) increased the spectral intensity by ~ 1.3 times, owing to densification of the laser-induced plasma. Linearity in the calibration curve of P at 213.6 nm in soil was maintained up to ~ 0.5 wt%, whereas saturation occurred beyond ~ 1 wt%. In contrast, no linearity was observed in the calibration curve of K at 766.5 nm. The LIBS intensity correlated with the plant-available content; however, the magnetic-field-induced sensitivity enhancement contributed little to accuracy improvement. The spatial heterogeneity of actual soil leads to analytical errors, underscoring the importance of soil sample homogenization.