R2, coefficient of regression; MBE, Mean bias error;
RMSE, Root mean square error; RPD, ratio of performance to deviation.
MARS, Multivariate adaptive regression splines; PCR, Principal component
regression; PLSR, Partial least square regression; RF, Random forest;
SVR, Support vector regression.
pH, soil pH; EC, Electrical conductivity; SOC, Soil organic carbon; BD,
Bulk density; N, Soil available nitrogen; P, Soil available phosphorus;
K, Ammonium extractable potassium; Na, Ammonium extractable sodium; Ca,
Ammonium extractable calcium; Mg, Ammonium extractable magnesium; S,
soil available sulphur; Fe, soil available iron; Mn, Soil available
manganese; Cu, Soil available copper; Zn, Soil available zinc; B, Soil
available boron.
PC, Principal component; mtry, ; γ, sigma ; c, cost.