Table 5.

Performance results (validation R²≥0.5) of trialled preprocessing and multivariate methods for the prediction of nitrogen in wheat.

Calibration
		PLSR	PCR	MLR	RF	SVM
SMO	R2	0.56	0.50	0.53	0.42	0.60
	RMSE	0.42	0.45	0.43	0.48	0.40
	RPD	1.49	1.40	1.46	1.31	1.58
Raw	R2	0.59	0.49	0.48	0.42	0.62
	RMSE	0.41	0.45	0.45	0.47	0.39
	RPD	1.53	1.38	1.39	1.32	1.60
Validation
		PLSR	PCR	MLR	RF	SVM
SMO	R2	0.59	0.54	0.57	0.33	0.43
	RMSE	0.41	0.44	0.42	0.52	0.48
	RPD	1.56	1.47	1.53	1.22	1.33
Raw	R2	0.57	0.52	0.58	0.33	0.43
	RMSE	0.42	0.44	0.42	0.52	0.48
	RPD	1.53	1.44	1.54	1.23	1.33

R² = coefficient of determination, RMSE; root mean square error; RPD; ratio of performance to deviation. PLSR; partial least-squares regression; PCR; principal components regression; MLR; multiple linear regression; RF; random forest; SVM; support vector machine; SMO; smoothed.