Table 4.

Effect of background correction and normalization of spectra on multivariate methods, reported as coefficients of determination, in the case of Ca, values in parentheses show the effect of using the logarithms of the mass fractions.

Element	Averaged Raw Spectra			Background Corrected, Normalized and Averaged Spectra
	PLSR	Lasso	GPR	PLSR	Lasso	GPR
Ca	0.82 (0.68)	0.84 (0.59)	0.86 (0.82)	0.86 (0.87)	0.84 (0.85)	0.83 (0.89)
Mg	0.73	0.71	0.75	0.79	0.75	0.78
K	0.60	0.64	0.60	0.64	0.65	0.66
N	0.48	0.56	0.41	0.51	0.65	0.51
P	0.18	0.16	0.26	0.14	0.21	0.28
Fe	0.69	0.63	0.64	0.77	0.76	0.72
Mn	0.15	0.07	0.01	0.21	0.55	0.13
Al	0.72	0.65	0.71	0.79	0.74	0.81
P (pa)	0.25	0.09	0.37	0.22	0.25	0.35
Humus	0.58	0.41	0.50	0.56	0.66	0.54
pH	0.86	0.77	0.93	0.91	0.92	0.95
mean	0.52	0.47	0.52	0.55	0.61	0.57
change				6%	31%	11%