Table 2.

The modeling results of different soils and temperatures by SPA-MLR. RMSEC: root mean square error (RMSE) of the calibration set; RMSEP: RMSE of the prediction set; RPD: residual predictive deviation.

Group	Soil Type	Calibration Set			Prediction Set
		N1	Rc	RMSEC (g/kg)	N2	Rp	RMSEP (g/kg)	RPD
1 (50 °C)	Black soil	118	0.9725	0.11	58	0.9486	0.22	2.82
	Loess	118	0.9649	0.072	58	0.9265	0.13	2.34
	Calcium soil	118	0.9681	0.039	58	0.9290	0.120	2.63
2 (80 °C)	Black soil	118	0.9203	0.251	58	0.9373	0.234	2.55
	Loess	118	0.9727	0.067	58	0.9541	0.090	3.20
	Calcium soil	118	0.9492	0.108	58	0.9320	0.162	2.12
3 (95 °C)	Black soil	118	0.9692	0.156	58	0.9132	0.282	2.16
	Loess	118	0.9660	0.075	58	0.9758	0.070	4.35
	Calcium soil	118	0.9670	0.087	58	0.9517	0.103	3.24
4 (25 °C)	Black soil	118	0.6061	0.486	58	0.7129	0.418	1.25
	Loess	118	0.5473	0.247	58	0.6217	0.246	1.20
	Calcium soil	118	0.4391	0.302	58	0.5824	0.365	0.94