عنوان مقاله [English]
Introduction: Iron is found in different forms in the soil. In the primary minerals, iron is found as Fe3+ or Fe2+ which converted to Fe2+ and released in unsuitable reduction conditions. Minerals such as sulfide or chlorine and bicarbonate can affect and change the different forms soil Fe. FeAs these elements are abundance in groundwater or soil, they are capable to react chemically with Fe and change different Fe forms and also may deposit or even leach them by increasing its solubility in the soil. Water table fluctuation is a regular phenomenon in Khuzestan that Fe forms change under these situations. The study of Fe oxide forms and its changes can be applied for evaluation of soil development. Therefore, the aim of this study is the water table fluctuation and its quality effects, and some physio-chemical properties on Fe oxides forms in non-saline and saline soils in Khuzestan.
Materials and Methods: Soil samples were collected from two regions: saline (Abdolkhan) and non-saline (South Susa) regions. soil samples were collected from all horizons of 12 soil field studied profiles . The samples were analyzed for soil texture, pH, EC (soil: water ratio 1:5), organic carbon and aggregate stability (Kemper and Rosenau method). Fe forms also were extracted by two methods in all samples: di-tyonite sodium and ammonium oxalate extraction. Fe oxalate extracted was related to Feo (non crystal Fe) and Fed-Feo was related to Fec (crystalline Fe). The Fe content were determined by atomic absorbtion spectrophotometer (AAS). Data were analysis in SAS and Excel software and results were presented.
Results and Discussion: The results showed that texture were loamy sand to silty clay loam, OM was very poor (0.1-0.7%). The soil salinity was also 2.8-16.8 dS/m. Calcium carbonate equivalent was 38-40%. All pedons were classified in Entisols and Inceptisols according to Keys to soil taxonomy (2010). The results showed that the proportion of Fe with oxalate to di-tionite treatments was different regarding the salinity, texture, organic matters, cultivation and the water table fluctuation. The total Fe content in the middle layers had permanently increased due to the groundwater fluctuation levels and this caused the creation of mottle in this layer. All saline soils had saline subsurface water. The salinity has caused that the effective microorganisms have not been actived on the reduction processes in some profiles and the Fe deposit more in the Fe3+forms. The Fe was found more in non-crystal form in saline regions, but it was in the crystal form in non-saline regions which indicated the suitable conditions for Fe’s nodule formation. For example, when soil salinity decreased from 14.9 to 8.1 dS/m, Fec increased from 460.1 to 497.8 mg/kg soil. With increasing the amount of clay, and cultivation periods, the Fed content has also been increased. The Feo/ Fec ratio in undevelopted soils was higher than developed soils. This ratio was low in non-saline soil and was high for saline soil. this indicates that non-saline soil had more development than saline soils. The maximum amount (1.6) was belonged to saline soil and minimum was for no saline soils. With increasing in soil age, tillage periods and clay content this ratio was decreased., statistical analysis Also showed that there was significant difference between Fec and Feo in saline and no saline soils. Also, with increasing in salinity, Fec content decreased and Feo increased. aggregate stability was also increased with increasing Fec content.
Conclusions: The Feo content was more in surface of saline soil than subsurface when pedon was ponded and saturated from surface. Feo was very higher in saline soils than no saline soils. Fec had not significant difference between saline and nonsaline soils. Salinity decreased Fec and increased Feo content in soils. Feo/Fec ratio of saline soils was 4 to 5 times fold of non-saline soils. Increasing Feo/Fec ratio in saline soils and decreasing in this ratio in nonsaline soil showed that nonsaline soils had more development than saline soils. Organic matter was more effective in Feo and Fec contents in nonsaline soil than saline soils. Also, Fec content increased with increasing clay content in all horizons that this shows that mottling and more Fe concentration in nonsaline soils.