Comparison of multivariate methods for estimating soil total nitrogen with visible/near-infrared spectroscopy

Aims This study aimed to compare stepwise multiple linear regression(SMLR), partial least squares regression(PLSR) and support vector machine regression(SVMR) for estimating soil total nitrogen (TN) contents with laboratory visible/near-infrared reflectance (Vis/NIR) of selected coarse and heterogeneous soils. Moreover, the effects of the first (1st) vs. second (2nd) derivative of spectral reflectance and the importance wavelengths were explored.