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

Table 5

Optimal selection of the preprocessing technique using the Si-PLS model.

Parameters	Preprocessing	Calibration set (77)			Prediction set (33)
		R^2	RMSEC	Bias	R^2	RMSEP	Bias
N (%)	RAW	0.5540	0.0337	0.0001	0.6571	0.0348	−0.0141
	MSC	0.5158	0.0349	0.0012	0.5307	0.0378	−0.0130
	MC	0.5549	0.0338	−0.001	0.3845	0.0414	−0.0139
	SNV	0.5160	0.0348	0.0000	0.3220	0.0455	−0.0178
	FD	0.5713	0.0333	0.0005	0.6993	0.0335	−0.0139
P (mg·kg^−1)	RAW	0.7714	0.7809	0.0289	0.8382	0.6815	0.0870
	MSC	0.7551	0.8025	0.0310	0.8129	0.7244	0.0432
	MC	0.7779	0.7699	0.0438	0.8360	0.6880	0.0979
	SNV	0.7549	0.8024	0.0304	0.7982	0.7573	−0.0289
	FD	0.7796	0.7659	0.0284	0.8042	0.7381	0.0488
K (cmolc·kg^−1)	RAW	0.9044	0.0859	0.0005	0.8496	0.1360	−0.0554
	MSC	0.8921	0.0911	0.0032	0.8310	0.1318	−0.0355
	MC	0.9092	0.0838	0.0001	0.8804	0.1254	−0.0501
	SNV	0.8966	0.0892	0.0004	0.8593	0.1229	−0.0319
	FD	0.9108	0.0833	0.0005	0.8980	0.1176	−0.0470
Mg^2+(cmolc·kg^−1)	RAW	0.8010	0.4699	0.0071	0.7586	0.6835	0.0178
	MSC	0.7961	0.4809	0.0116	0.8205	0.5591	0.0532
	MC	0.8066	0.4655	0.0066	0.7976	0.6100	0.0175
	SNV	0.7893	0.4825	0.0028	0.8209	0.5704	0.0293
	FD	0.7786	0.4929	0.0160	0.7613	0.6542	0.1097
Ca^2+ (cmolc·kg^−1)	RAW	0.8342	2.1857	0.1060	0.6470	3.0853	−0.1829
	MSC	0.8160	2.3095	0.0142	0.3827	3.9873	−0.4315
	MC	0.8317	2.2040	0.0507	0.6712	3.0206	−0.5359
	SNV	0.8126	2.2983	0.0443	0.5245	3.4507	−0.0758
	FD	0.8269	2.2286	0.0642	0.6662	3.0219	−0.4531
pH	RAW	0.9043	0.3317	0.0004	0.6465	0.4760	−0.0369
	MSC	0.8790	0.3709	0.0052	0.5749	0.5162	0.0465
	MC	0.8927	0.3505	0.0093	0.5445	0.558	−0.0577
	SNV	0.8767	0.3755	0.0050	0.5931	0.5324	−0.0753
	FD	0.8901	0.3543	0.0071	0.5796	0.5105	−0.0040