جستجوی مقالات مرتبط با کلیدواژه « central zagros » در نشریات گروه « آب و خاک »

The amount of energy received from the sun on the ground needed to estimate crop water use, use of clean energy and issues related to climatic factors. In this study, the ability of two estimation methods based on statistical and dynamic methods were evaluated. Angstrom equation, as a widely accepted statistical model, and Regional Climate Model (RegCM version 4.0) were chosen to obtain radiation estimations. To perform this study, meteorological data of 6 IRIMO’s automatic weather stations located in Chaharmahal and Bakhtiari province, west of Iran, were used. RegCM4 model was run considering initial values and boundary conditions of NNRP1 ,at 18 sigmoid levels, with spatial resolution of 30 km and temporal resolution of 150 minutes, in the period of 2010 to 2014. Results showed the RegCM4 model output has the minimum Root mean square error (RMSE) of 10 W m-2 in warm months (June to September) and highest RMSE of 408 W m-2 in February. The lowest RMSE was obtained in September in Borujen station and the highest value was recorded in month of February in Ardal. The average value of overall RMSE in the region was 175 W m-2. Monthly values of Angstrom model was calibrated for study stations. The highest correlation coefficient and lowest RMSE and MBE were obtained for September. The maximum value of RMS was 321 W m 2 in April. Angstrom model showed an underestimation in 73% of the cases while RegCM showed an overestimation 93 % of the cases. These results tend to confirm the need for post processing of the climate model outputs.

Soil saturated hydraulic conductivity (Ks) is an essential property in managing irrigation projects, water and solute transport modeling and for predicting unsaturated hydraulic conductivity functions. Laboratory and field measurements of Ks are time-consuming and costly especially in the large scales. Moreover, Ks is affected by different factors and thus its predicting and modeling by derived pedotrasfer functions (PTFs) or those in the literature can be useful for many purposes. This study was performedto evaluate the already existed in literature and derived PTFs for predicting Ks in Farsan and Koohrang regions, Chaharmahal-va-Bakhtiari province in the central Zagros. Undisturbed samples (volume of 100 cm3) were collected from the surface soil at 100 locations which were well distributed in the region and in different land uses. The Ks of the undisturbed samples was measured using the constant-head method in laboratory. Easily-available soil properties were also determined and PTFs for Ks prediction were derived by multiple stepwise regression. The measured Ks values were also compared with the predictions of several PTFs in the literature. Results showed that PTFs in the literature could not accurately predict the Ks in the region. Among the literature PTFs, powerful neural network model of Rosetta (SCC) was the best. The worse PTFs for Ks prediction in the studied structured soils were Brakensiek et al. (1984) PTFs. However, the derived PTFs predicted the Ks in the region better (R2=52%, RMSE=0.5 mm/h) than the literature PTFs. The findings revealed that logarithm of Ks negatively correlates with relative bulk density (relative compaction), effective bulk density, clay to carbonate content (Clay/CaCO3) and carbonate to organic matter content (CaCO3/OM) ratios and bulk density and clay interaction [ln (BD×Clay)] and has positive correlations with OM, ln(OM/Clay), very fine sand content and soil porosity. The studied soils had good structure and the structural properties had significant role in the derived PTFs. Therefore, it is suggested to include additional structural properties such as aggregate's mean diameter as a predictor for better Ks prediction in future.

Free and uncontrolled pasture grazing by animals may decrease soil aggregate stability through reductions in plant cover and subsequent soil organic C، and trampling. This could expose the soil surface layer to degradation and erosion. The objective of this study was to determine the influence of pasture management (free grazing، controlled grazing and long-term non-grazing regimes) on aggregate-size distribution and aggregation parameters by wet and dry sieving methods in two native pastures، protected areas in Chaharmahal va Bakhtiari province. The studied pastures were 1) SabzKouh pastures protected from grazing for 20 years، and 2) Boroujen pastures protected from grazing for 25 years. Soil samples were collected from 0-15 cm depth during the grazing season in summer 2008. Samples (finer than 2 mm) were analyzed for aggregate-size distribution and aggregation parameters by wet and dry sieving methods. Results showed that pasture management had a significant influence on aggregate-size distribution and aggregation parameters in the two areas. The two methods indicated that macro-aggregates in non-grazing and controlled grazing regimes were higher than those in free grazing regime، whereas in free grazing management micro-aggregates showed an opposite trend، and were greater compared with the other grazing regimes. Similarly، soil aggregate stability indices (i. e. mean weight diameter، aggregate geometric and ratio mean diameter) were all improved by non-grazing regimes، suggesting that animal grazing and trampling break down large soil aggregates due largely to compaction and reduced plant coverage. However، the extent to which grazing affects soil aggregation depends in large part on grazing intensity and duration، and the area involved.

Vegetation is the most important factor in sustainable and dynamic equilibrium of natural ecosystems. Considering the relation between environmental factors and vegetation is an essential step in order to identify the effective factors in the habitats. The purpose of this study was to evaluate the relations between vegetation and soil characteristics in rangelands of Ferydounshahr (Sardab-Sibak watershed). The flora and vegetation types were studied using Physionomic-floristic method in the field and eight vegetation types were identified. Vegetation was sampled by Systematic–randomized method in 1× 2 m plots. The canopy cover and species composition percentage were estimated in each plot. After digging a soil profile in vegetation types, the physical and chemical factors were measured. The influences of edaphic factors on vegetation were analyzed using RDA ordination technique. Results showed that based on soil characteristics the eight vegetation types can be classified in to three main range habitats including, Ferula ovina, Astragalus adscendens and Astragalus brachycalyx. The most important factors which cause the separation in these three habitat ranges were clay percentage, organic matter, soil depth, CaCO3, pavement and barren soil.

The effect of overgrazing on vegetation changes in central Zagros has been studied by a few scientists, but there is no detailed information on the impact of such practices on soil properties. The objective of this study was to assess the effect of climate and grazing management on selected soil biochemical properties. Fourteen experimental range sites protected against grazing as well as their adjacent overgrazed sites in Chadegan, Pishkuh and Poshtkuh were selected. In each site, samples were collected from the depths 0-5 and 5-15 cm. Soil organic C (OC), microbial biomass C (MBC), total nitrogen (TN), organic C to total N ratio (C/N), microbial biomass C to organic C ratio (Cmic/Coc) and metabolic quotient (qCO2) were measured and/or calculated. The results showed that the lowest SOC, MBC, TN and Cmic/Coc occur in Chadegan due to low fresh materials input. The above parameters in Pishkuh and Poshtkuh regions are 2.5 to 3 times greater than those in Chadegan area. Grazing intensity in Pishkuh is less than that in Poshtkuh region and there is no significant difference between grazed and protected sites in Pishkuh. But, there is a significant difference between grazed and protected plots in Poshtkuh due to a higher grazing intensity. Higher Cmic/Coc and lower qCO2 suggest that the quality of organic matter is better in Poshtkuh and Pishkuh. In conclusion, highly degraded rangelands in Pishkuh and Poshtkuh seem to be able to recover very quickly with proper management, while Chadegan region needs a much longer period of time to restore.