Effect of Selected Factors on the Prediction Accuracy of Plant-Available Phosphorus and Potassium: A Global Meta-Analysis for Infrared Spectroscopy Protocol

Chemical methods are reliable for soil testing, but they can be both time-consuming and expensive. This reason makes them unsuitable for quick analysis, especially for many soil samples. Infrared spectroscopy is a cutting-edge technique that offers promising alternative methods that are fast, cheaper, and environmentally friendly. Research findings show contradicting accuracy levels for the infrared protocol when predicting phosphorus (P) and potassium (K). For this reason, the study employed meta-analysis to investigate the effect of selected factors on the prediction accuracy of P and K. Studies that tested P and K in the laboratory using the protocol were selected. The results showed that concentration and soil sample size can significantly (p < 0.001) affect the prediction accuracy of these plant-available nutrients. A positive correlation was observed between the coefficient of determination (r2), sample size (r2 = 0.75 P, r2 = 0.68 K), and concentration (r2 = 0.62 P, r2 = 0.64 K). The variation observed in the dependent variable (r2) was explained mostly by sample size and concentration. This could be the source of the overall low prediction accuracy observed from the studies [r2 = 0.46, RPD = 1.44 (P) and r2 = 0.55, RPD = 1.55 (K)].