. 2020 Dec 10;15(12):e0242821. doi: 10.1371/journal.pone.0242821

Table 2. Correlation (R²) values for pXRF and MIR calibrations for total C, total N ash content, and major nutrients.

	pXRF Forest R²	pXRF XGBoost R²	MIR Forest R²	MIR XGBoost R²
Ash (%)	0.94	0.94	0.93	0.94
Total C (%)	0.97	0.92	0.95	0.95
Total N (%)	0.92	0.93	0.92	0.94
P (%)	0.94	0.89	0.92	0.87
K (%)	0.90	0.93	0.84	0.72
Ca (%)	0.98	0.95	0.83	0.81
Mg (%)	0.77	0.71	0.73	0.66
Na (%)	0.91	0.87	0.86	0.81
S (%)	0.98	0.91	0.93	0.83
Mn (%)	0.87	0.73	0.63	NA
Fe (%)	0.95	0.94	0.67	0.77
Zn (ppm)	0.95	0.94	0.00	0
Cu (ppm)	0.92	0.90	0.00	0
Ni (ppm)	0.92	0.97	0.00	0
Cd (ppm)	0.99	0.97	0.24	0
Pb (ppm)	0.95	0.98	0.00	0

For the calibrations, 67% of all organic amendment (OA) samples and Forest or XGBoost models were used.

Table 2. Correlation (R2) values for pXRF and MIR calibrations for total C, total N ash content, and major nutrients.