Visible and Near-Infrared Reflectance Spectroscopy for Investigating Soil Mineralogy: A Review

Table 2

A review of VNIR spectroscopy for the prediction of soil attributes using feature-based and chemometric methods in previous studies.

Soil mineralogic attribute^a	Soil type^b	Location	Sample^c	ncal/nval^d	Method^e	R^2f	RMSE^g	Source
ClayT	Alfisols and entisols	Romania	Lab/sieved (2)-air-dried	210/90	SVR	0.27	84.4	[90]
ClayT	Not mentioned	France	Lab/sieved (2)-air-dried	99/49	PLSR	0.76	33.6	[59]
ClayT	Diverse	Romania	Lab/sieved (2)-air-dried	210/90	SVR	0.46	85.3	[91]
ClayT	Vertisols and alfisols	India	Lab/sieved (2)-air-dried	175/58	PLSR	0.80	2.2	[92]
ClayT	Diverse	Denmark	Lab/sieved (2)-air-dried	480CV	PLSR	0.94	17	[84]
ClayT	Entisol and inceptisols	Italy	Lab/sieved (2)-oven-dried	175/60	PLSR	0.80	0.17	[93]
ClayT	Diverse	Australia	Lab/sieved (2)-air-dried	1104CV	DWT-ANN	0.88	64.2	[45]
ClayT	Diverse	Australia	Lab/sieved (2)-air-dried	1104CV	PLSR	0.83	77.7	[45]
ClayT	Entisol	Turkey	Lab/sieved (2)-air-dried	502CV	PLSR	0.84	38.20	[89]
ClayT	Entisol	Turkey	Lab/sieved (2)-air-dried	502CV	MARS	0.86	35.10	[89]
ClayT	Diverse	France	Lab/sieved (2)-oven-dried	52CV	PLSR	0.85	31.2	[22]
ClayT	Diverse	France	Lab/sieved (2)-oven-dried	52CV	CR	0.73	44	[22]
ClayT	Diverse	France	Field/fresh	52CV	PLSR	0.64	49.6	[22]
ClayT	Diverse	France	Field/fresh	52CV	CR	0.58	82	[22]
ClayT	Diverse	USA	Lab/sieved (2)-air-dried	72CV	PLSR	0.92	41	[85]
ClayT	Diverse	USA	Field/fresh	72CV	PLSR	0.83	61	[85]
ClayK	Diverse	Australia	Lab/sieved (2)-air-dried	102CV	PLSR	0.95	111.5	[94]
ClayK	Not mentioned	China	Lab/sieved (2)-air-dried	20CV	CR-MLR	0.80	10.41	[88]
ClayK	Diverse topsoil	Australia	Lab/sieved (2)-air-dried	4606CV	Model trees	0.52	0.8	[95]
ClayK	Diverse subsoil	Australia	Lab/sieved (2)-air-dried	2492CV	Model trees	0.46	1.1	[95]
ClayK	Mineral-organic mixes	Australia	Lab/sieved (0.2)-oven-dried	8CV	PLSR	0.94	0.36	[2]
ClayI	Diverse	Australia	Lab/sieved (2)-air-dried	90CV	PLSR	0.96	102.1	[94]
ClayI	Not mentioned	China	Lab/sieved (2)-air-dried	20CV	CR-MLR	0.79	28.14	[88]
ClayI	Diverse topsoil	Australia	Lab/sieved (2)-air-dried	4606CV	Model trees	0.41	1.2	[95]
ClayI	Diverse subsoil	Australia	Lab/sieved (2)-air-dried	2492CV	Model trees	0.40	1.5	[95]
ClayI	Mineral-organic mixes	Australia	Lab/sieved (0.2)-oven-dried	8CV	PLSR	0.96	0.34	[2]
ClayS	Diverse	Australia	Lab/sieved (2)-air-dried	98CV	PLSR	0.94	118.7	[94]
ClayS	Not mentioned	China	Lab/sieved (2)-air-dried	20CV	CR-MLR	0.84	21.35	[88]
ClayS	Diverse	France	Lab/sieved (2)-air-dried	63CV	CR	0.83	158	[20]
ClayS	Diverse topsoil	Australia	Lab/sieved (2)-air-dried	4606CV	Model trees	0.61	0.8	[95]
ClayS	Diverse subsoil	Australia	Lab/sieved (2)-air-dried	2492CV	Model trees	0.44	1.2	[95]
ClayS	Mineral-organic mixes	Australia	Lab/sieved (0.2)-oven-dried	8CV	PLSR	0.92	0.34	[2]
ClayS	Not mentioned	USA	Lab/sieved (2)-air-dried	178CV	PLSR	0.83	1	[96]
Clay2:1	Argiudoll, hapludolls, and eutrudox	Brazil	Lab/sieved (2)-oven-dried	29CV	CR	0.80	—	[47]
FeT	Not mentioned	France	Lab/sieved (2)-air-dried	99/49	PLSR	0.84	24^h	[59]
FeT	Vertisols and alfisols	India	Lab/sieved (2)-air-dried	175/58	PLSR	0.78	0.15^h	[92]
FeT	Diverse	Moravia	Lab/sieved (2)-air-dried	97CV	MLR	0.37	12.76^h	[97]
FeT	Cambisols and luvisols	South Africa	Lab/sieved (2)-air-dried	123/40	CR-MLR	0.21	9.3	[98]
FeT	Cambisols and luvisols	South Africa	Field/fresh	94/31	CR-MLR	0.23	16.3	[98]
FeT	Cambisols and luvisols	South Africa	Lab/sieved (2)-air-dried	123/40	PLSR	0.43	9.8	[98]
FeT	Cambisols and luvisols	South Africa	Field/fresh	94/31	PLSR	0.43	8.0	[98]
FeH	Typic hapludox and typic eutrudox	Brazil	Lab/sieved (2)-air-dried	206CV	PLSR	0.77	10.7	[99]
FeG	Fe-oxide mixes	USA	Lab/sieved (2)-oven-dried	6CV	CR	0.95	25.3	[86]
C	Entisols, inceptisols, and aridisols	Iran	Lab/sieved (2)-air-dried	30/10	PLSR	0.71	52.4	[67]
C	Not mentioned	France	Lab/sieved (2)-air-dried	99/49	PLSR	0.89	42.1	[59]
C	Diverse topsoil	Iran	Lab/sieved (2)-air-dried	251CV	PLSR	0.58	117	[100]
C	Diverse topsoil	Iran	Lab/sieved (2)-air-dried	251CV	CR	0.35	149	[100]
C	Entisol	Turkey	Lab/sieved (2)-air-dried	502CV	PLSR	0.65	6.80	[89]
C	Entisol	Turkey	Lab/sieved (2)-air-dried	502CV	MARS	0.71	6.20	[89]
C	Diverse	France	Lab/sieved (2)-oven-dried	52CV	PLSR	0.94	38.34	[22]
C	Diverse	France	Lab/sieved (2)-oven-dried	52CV	CR	0.92	52	[22]
C	Diverse	France	Field/fresh	52CV	PLSR	0.77	76.67	[22]
C	Diverse	France	Field/fresh	52CV	CR	0.47	132	[22]

^aSoil attributes: clay_T, total clay content; clay_2:1,2:1 clay mineral content; Clay_K, kaolinite content; Clay_I, illite content; Clay_S, smectite content; Fe_T, total iron content; Fe_H, hematite content; Fe_G, goethite content; C, carbonate content. ^bsoil type: soil type is not given in the study (not mentioned); the soil samples in the study include more than three soil types (diverse). ^csample treatment: oven-dried, sieved (<2 mm), and measured under laboratory conditions (lab/sieved (2)-oven-dried); oven-dried, sieved (<0.2 mm), and measured under laboratory conditions (lab/sieved (0.2)-oven-dried); air-dried, sieved (<2 mm), and measured under laboratory conditions (lab/sieved (2)-air-dried); fresh (wet and unprocessed) and measured under field conditions (field/fresh). ^dn_cal/n_val shows the number of samples used in the spectral calibration and validation, respectively. CV indicates that the validation was conducted independently using a statistical cross-validation technique. ^epartial least squares regression (PLSR); multivariate adaptive regression splines (MARS); support vector regression (SVR); the discrete wavelet transform-artificial neural networks (DWT-ANN); continuum removal (CR); feature-based multiple linear regression (CR-MLR). ^fcoefficient of determination. ^groot mean-square error (g·kg⁻¹). —, RMSE is not given in the study. ^hmg·kg⁻¹.