3.4.13 Soil Mn prediction
Excellent predictions (R2c=0.99;
MBEc=-0.72; RMSEc=2.16;
RPDc=3.34) were obtained using the SVR model for Mn
(Figure 4m). The MARS models also recorded an excellent prediction
(R2c=0.93; MBEc=-0.25;
RMSEc=3.19; RPDc=2.25). Though the
predictions for calibration using SVR and MARS were excellent, the
validation predictions using PCR
(R2p=0.73; MBEp=-0.84;
RMSEp=6.20; RPDp=1.24) and PLSR
(R2p=0.52; MBEp=-0.89;
RMSEp=6.04; RPDp=1.28) were better than
other models tested. These results of prediction were considered as
non-reliable. The results pertaining to Mn are in agreement with those
reported by Janik et al. , (1998), who recorded
R2 of 0.57 and 0.66 to predict DTPA extractable-Mn and
exchangeable-Mn using the PLSR analysis of the MIR spectral data
(2500-25000 nm). Mehlich-III extractable-Mn could be monitored using PCR
of the VIS–NIR (400–2498 nm) with an accuracy of
R2=0.70 (Chang et al. , 2001). Similar to Fe, Mn
also showed poor prediction accuracy and this is in accordance with
Vendrame et al. (2012) who reported poor prediction with
R2=0.35 and RPD=1.1 using multivariate analysis of NIR
spectral data to predict soil MnO2 content.