Quick Determination of Soil Quality Using Portable Spectroscopy and Efficient Multivariate Techniques

Table 6

Modelling results from different variable selection models for soil quality parameters.

Parameters	Models	Var	Wavelengths (nm), selected	Calibration (77)			Prediction (33)
				R^2	RMSEC	Bias	R^2	RMSEP	Bias
N (%)	PLS	331	740–1070	0.560	0.033	0.0038	0.777	0.026	0.004
	IPLS	17	842–858	0.441	0.036	−0.0002	0.413	0.038	−0.005
	Si-PLS	43	770–784 945–958 973–986	0.571	0.033	−0.0005	0.699	0.033	−0.013
P (mg·kg^−1)	PLS	331	740–1070	0.763	0.789	0.0900	0.803	0.684	0.119
	IPLS	17	1039–1054	0.698	0.882	0.0144	0.758	0.817	0.093
	Si-PLS	45	768–781 894–907 950–963 1058–1070	0.779	0.765	0.0284	0.804	0.738	0.048
K (cmolc·kg^−1)	PLS	331	740–1070	0.878	0.096	0.0110	0.878	0.107	0.018
	IPLS	17	842–858	0.798	0.121	−0.0019	0.732	0.134	0.016
	Si-PLS	60	846–860 876–890 921–935 996–1010	0.910	0.083	0.0005	0.898	0.117	−0.047
Mg^2+ (cmolc·kg^−1)	PLS	331	740–1070	0.711	0.550	0.0627	0.807	0.568	0.098
	IPLS	17	1055–1070	0.770	0.502	0.0008	0.776	0.608	−0.025
	Si-PLS	53	768–781 824–836 967–979 1019–1030	0.778	0.492	0.0160	0.761	0.654	0.109
Ca^2+ (cmolc·kg^−1)	PLS	331	740–1070	0.783	2.439	0.2780	0.787	2.470	0.430
	IPLS	17	774–790	0.736	2.652	0.0119	0.734	2.8916	−0.9689
	Si-PLS	60	756–770 801–815 936–950 981–995	0.826	2.228	0.0642	0.666	3.0219	−0.4531
pH	PLS	331	740–1070	0.891	0.351	0.0401	0.785	0.3655	0.0636
	IPLS	17	876–890	0.688	0.564	0.0407	0.500	0.5301	0.1165
	Si-PLS	53	810–823 824–837 922–935 1019–1031	0.904	0.331	−0.0004	0.646	0.4760	−0.0369

Par: quality parameter, Var: selected variable. Bold values represents best options.