The present work was designed to study the pH, sand, silt, clay, lime, organic carbon (OC), cation exchange capacity and heavy metals (Fe, Mn, Cu and Zn) in agricultural soils of Mashhad plain, Northeastern Iran. Pearson's correlation analysis showed that OC influenced the retention of Cu and Mn in both surface and subsurface agricultural soil samples. The results of contamination factor, pollution index and potential ecological risk (RI) indicated low pollution of Mn, Zn and Cu in the agricultural soil samples. The enrichment factor showed very high enrichment of heavy metals in surface (88.1%) and subsurface (79.1%) agricultural soil samples. The geoaccumulation index also indicated very high contamination of heavy metals in surface (87.5%) and subsurface (82.6%) soil samples. The modified potential ecological risk (MRI) showed 37.5% ecological risk in surface, and 32.5% ecological risk in subsurface soil samples of Mashhad plain, Northeastern Iran. Abbreviation: Fe: Iron; Mn: Manganese; Cu: Copper; Zn: Zinc; PCA: Principal component analysis; CA: Cluster analysis; CF: Contamination factor; EF: Enrichment factor; Igeo: Geoaccumulation index; PI: Pollution index; MPI: Modified pollution index; RI: Potential ecological risk index; MRI: Modified potential ecological risk index.
Keywords: Agricultural soil; heavy metals; multivariate techniques; pollution indices.