Improving the performance of a spectral model to estimate total nitrogen content with small soil samples sizes

Chemical and Biological Technologies in Agriculture

Table 4 Regression results of using different particle sizes soil data

Data (n=111)	Best method^[1]	Calibration		Validation
Data (n=111)	Best method^[1]	\(R^2_c\)	\(RMSE_c (g.kg^{-1})\)	\(R^2_v\)	\(RMSE_v (g.kg^{-1})\)
Pristine mixed soil data	GPR	0.737	0.132	0.543	0.118
0.1 - 0.2mm data	UVE-PLSR	0.613	0.148	0.505	0.124
0.5 - 0.1mm data	GPR	0.739	0.132	0.570	0.107
0.25 - 0.50mm data	GPR	0.855	0.093	0.575	0.110
0.15 - 0.25mm data	Cubist	0.719	0.139	0.631	0.098
0.09 - 0.15mm data	Cubist	0.697	0.139	0.583	0.102
< 0.09mm data	GPR	0.542	0.157	0.490	0.128

\([1]\) Best method means implemented to get the optimum results among all methods