A GEOCHEMICAL INVESTIGATION OF PADDY (P) AND NON- PADDY (NP) SOILS ON A CATENA: A CASE STUDY OF GHAEMSHAHR IN MAZANDARAN PROVINCE, IRAN

Paddy soils are a main soil resource for food production and they cover a large area of the world's surface. A geochemistry study was performed on a catenary sequence of Paddy and Non-Paddy soils in the lowland and upland areas of Ghaemshahr City in Mazandaran Province, Iran. 10 soil profiles were investigated and then, a comparison was made between the Paddy and Non-Paddy soils based on their geochemical compositions and developments. Soil clay mineralogical analysis showed that the Non-Paddy soils had a large amount of vermiculite, whereas smectite was the dominant clay mineral of the Paddy soils. The cation exchange capacity, clay content, and bulk density are higher in the Paddy soils. Rice cultivation increases the amount of amorphous Fe and decreases the amount of free Fe-oxide. The results of free Fe-oxide and amorphous Fe assessments, revealed that the Non-Paddy and upland soils were more developed than the Paddy and lowland soils. The mean concentrations of the major elements did not show any significant differences between the two types of soils. The mean values of all the heavy metals, except for Mn and As, in the Paddy soils were lower than those of the Non-Paddy soils. The reason for the reduction of heavy metals in the P compared to NP soils was their probable relationships with Fe/Mn oxide minerals and subsequent leaching. Based on principal component analysis, the differences between the Paddy and Non-Paddy soils were related to Mn and Fe group elements. The results indicated that the concentrations of the elements and other properties of the Paddy soils were dependent on the soil parent materials, especially on the textures of the sedimentary layers.