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.