فهرست مطالب m. h. salehi

The kinetics of potassium release may be affected by P When phosphorus (P) fertilizer is applied to soils. The objective of this study was to the effect of Ca(H2Po4)2 fertilizer on the kinetics of non-exchangeable potassium (NEK) release in 10 calcareous soils. The amount of 100 mg kg-1 of P as Ca(H2Po4)2 was added to the soils. Treated and untreated soils were incubated at 70% of field capacity and 25±1°C for 90 days. After that, the NEK release was studied by 0.01 M CaCl2 extractant in 2017 hours by successive extraction methods in the treated and untreated soils. The results showed the NEK released in treated soils less than in untreated soils. The mean cumulative NEK released after 2017 h in the treated and untreated soils was 260.6 and 303.3 mg kg-1, respectively. The release of NEK in all soils was fast in the initial stages and continued at a lower speed in the later stages until the end of the experiment. The kinetics of NEK release was evaluated using kinetic equations. Based on the highest coefficients of determination (R2) and the lowest standard error (SE), the kinetics of NEK release in treated and untreated soils were described by the power function equation. The results of this research could be helpful for the precise fertilizer recommendation for the study in calcareous soils.

 In addition to the minerals, weathering in soil which depends on soil forming factors and processes, plants rhizosphere release components which affect soil minerals and finally their weathering. If the soil is polluted by heavy metals, root exudates will be influenced resulting in decreasing microbial activity. Many studies showed minerals weathering in rhizospheric medium for both natural soils and pure clay minerals but information about the effect of pollution of rhizosphere on clay minerals weathering is limited. This study was conducted to investigate the effect of cadmium pollution on the transformation of clay minerals in wheat rhizosphere in a dominant soil of Shahrekord plain (Chaharmahal soil series).

 Soil samples were collected from 0-20 cm depth of Chaharmahal soil series based on the 1:50,000 scale soil map. A factorial experiment as completely randomized design with three replications and three cadmium levels (0, 5, and 10 mg kg-1 from cadmium) was performed in two environments including bulk soil and rhizospheric soil (18 samples in total) in greenhouse conditions for 16 weeks. Necessary care was taken during the growth period and the soil moisture was kept constant at the field capacity. At harvest time, the rhizosphere soil was separated from bulk soil. Then, the soil samples were air dried and passed through a 2 mm sieve. The mineralogy was examined by X-ray diffraction (XRD) in the studied soil after plant harvest (including rhizospheric soil and bulk soil) in unpolluted samples. Then, results were compared with minerals in polluted rhizosphere media. Dissolved organic carbon (DOC) and pH in the rhizosphere and bulk soils were also determined.

The results showed that the effect of contamination on soil pH was not significant but the pH value in rhizosphere soil was significantly lower than the bulk soil. The average pH in the soil was 7.8 and in the rhizosphere reduced to 7.5. The interaction of medium (rhizosphere and bulk soil) and contamination on the amount of dissolved organic carbon was significant (p < 0.01). The amount of dissolved organic carbon in the rhizosphere at 170.6 mg Kg-1 was significantly higher than the bulk soil (104.6 mg kg-1), which could be due to root secretions. In the rhizosphere, increasing the contamination level to 5 mg kg-1 decreased by 19% and contamination of 10 mg kg-1 caused a 21% decrease in dissolved organic carbon. The amount of dissolved organic carbon in the rhizosphere was 39% higher than the bulk soil. The average of dissolved organic carbon in the rhizosphere and bulk soil was 170.6 and 104.6 mg kg-1, respectively. Based on mineralogical results, mica, smectite, chlorite, kaolinite and palygorskite minerals were detected in the bulk soil. Comparison of clay minerals samples in the bulk soil and rhizosphere showed that the trioctahedral chlorite transformed to hydroxy-interlayer vermiculite (HIV) in the rhizosphere soil. The presence of HIV was identified by an increase in the intensity ratio of the 10 and 14 angstrom peaks after K-saturation. In rhizospheric soils, the intensity of the 14 angstrom peak decreases in K-550ºC treatment. Furthermore, in the rhizospheric soils, a clear increase in the intensity of the 10 angstrom peak was observed from K-air dried to K-550ºC treatments which can be related to the presence of HIV which can be attributed to the changing conditions of the rhizosphere, including reducing pH and increasing the dissolved organic carbon and the activity of microorganisms. Comparison of diffractograms for clay fraction of rhizospheric soil with different contamination levels after cultivation showed that the type of minerals in contaminated levels was similar to non-contaminated conditions, but the amount of trioctahedral chlorite was the highest in higher contaminated soil. The peak intensity of 14 angstrom in potassium saturated sample heated at 550°C was lower in non-contaminated soil. Also, at the level of 10 mg kg-1 cadmium contamination, the chlorite peak had the highest intensity which indicates less chlorite was transformed to HIV in the contaminated soils.

The results showed that DOC in the rhizosphere soil was significantly higher than the bulk soil, whereas pH significantly decreased in the rhizosphere soil compared to the bulk soil. In both the rhizosphere and the bulk soils, increasing the contamination caused a decreasing trend in dissolved organic carbon. Mineralogical results of the rhizospheric and the bulk soils showed that trioctahedral chlorite was transformed to hydroxy-interlayer vermiculite (HIV). In addition, rhizosphere contamination reduced the chlorite transformation. The results suggest that soil contamination with a negative impact on plant activity and soil could even prevent the availability of nutrients from the clay minerals structure.

Geopedology is a systematic approach of geomorphic analysis for soil mapping which focuses the field operation mainly on sample area. The purpose of this study is to determine the credibility of generalization of the results of geopedological approach for similar landforms in the Borujen region, using diversity and similarity indices in a soil taxonomic hierarchical structure. After a primary interpretation of the study area on air photos (1:20000 scale), the largest delineation of Pi111 geomorphic unit was selected and 19 pedons with an approximate 125 m interval were excavated, described and sampled. The credibility of generalizing the results of the geopedological approach for the studied unit was tested by comparison with 15 pedons in a similar unit outside the sample area, named the validation area. Results showed that as the category decreases from order to soil family, the Shannon's diversity index increases in both the sample and validation areas. A significant difference at 95% confidence level was observed for pedodiversity mean values of two areas at family level. Soil diversity also remains high through the soil taxonomic hierarchy when we change the understanding level and consider the horizon/genetic diversity in both the sample and validation areas. Jaccard index and proportional similarity also indicated that up to subgroup level, the geopedological approach can be used for generalization of the similar geomorphic unit results and it does not have a good efficiency for lower soil taxonomic levels (family and series). Therefore, the use of landform phases and also phases of soil families and/or series for each of landform phases is recommended to increase the accuracy of geopedological results.

Clay minerals have considerable effects on physico-chemical properties of soils. Using different techniques, mineralogy of silicate clays and their formation were investigated in selected soils from Chaharmahal and Bakhtiari Province. The study area is about 1300 ha and its soil moisture and temperature regimes are xeric and mesic, respectively. Geomorphologically, the area consists of different landforms including pediments, outwash, hills and piedmont plain. After field and laboratory studies, five representative pedons were selected in previously determined mapping units and samples were taken for the analyses required. Clay particles from two surrounding rock formations and selected soil samples were separated and examined by electron microscopy (SEM and TEM), X-ray diffraction and infrared techniques. Illite, smectite, chlorite, palygorskite and kaolinite were present in all the soils. Considering the fact that palygorskite was not observed in nearby rock formations, this mineral is probably formed by pedogenic processes. Smectite, on the other hand, has been inherited from parent materials and also transformed from palygorskite. Other minerals had been probably inherited from parent materials. Infrared spectra confirm the X-ray diffraction and submicroscopic results.