Soil Fractions Mineralogy in Some Long term Cultivations with Xeric Moisture Regimes

The identification of soil fractions minerals types that have different vegetations is a matter of special importance. The aim of this study is investigation of the soil particles’minerals under continues cultivation. Hence, three different regions with similar soil moisture regime (xeric) including Gyan, Doroud and Kangavar plains were selected. Then 13 pedons with different properties and crops’cultivation history were selected and soil profiles were dug and analysed. The selected soils were under cultivation of rice, wheat, canola and sugar beet. Soil samples were collected from different horizons and their physicochemical and mineralogical characteristics were measured in the laboratory. All size fractions were separated and content of minerals in sand, silt and clay fraction was determined. X-ray diffraction, TEM and SEM analysis results from clay fraction in rice cultivation indicated that the most semi quantitative of minerals is sequential: chlorite> vermiculite> smectite> illite. The ponding condition provided a suitable posotion for stability of chlorite and vermiculite minerals. The presence of vermiculite in paddy rice might cause biotite weathering. The most of smectite content was observed in clay fraction in sugar beet cultivation and then in canola cultivation. The neoformation of smectite containing Ca as exchangeable cation was dominant in cultivated soils. The mixed minerals as vermiculite–chlorite, illite- smectite and illite-vermicultie were predominantly observed in silt fraction under rice cultivation and then in sugar beet and canola cultivations. The variability of sand fraction mineral was negligible and it was similar in all cultivation almost.