فهرست مطالب مهناز ختار

Fire affects all components of the ecosystem and reduces its quality. In this study, to investigate the effect of fire on soil properties, burned and control soil samples were taken from the surface depth (0-30 cm) during three years 2018-2020 from the Solan region of Hamadan; then, organic carbon, phosphorus, and potassium, salinity, pH, lime, sand, clay, and silt were measured. The results showed that the fire increased the percentage of sand (12.75%) and decreased silt and clay percentage (12.09 and 0.66%, respectively). Available soil phosphorus increased (90.32%) in the burned treatment. Lime and soil pH levels were very close in both control and burned treatments. The amount of organic matter (30%), available potassium (8.45%), and soil salinity (more than 16%) decreased in burn treatment. During the three years after the fire occurrence, the percentage of sand increased, and the lime percentage and soil salinity decreased; however, the other characteristics did not show a definite trend of changes. According to the results, it is necessary to prevent intentional and unintentional fires with proper management of natural ecosystems. In case of such incidents, these areas should be rehabilitated and their production capacity strengthened by increasing organic matter and soil organisms.

Daily increasing salinity is one of the main problems of agricultural lands, especially in arid and semi-arid regions, with high evapotranspiration rates. The purpose of this research was to investigate the simultaneous effect of salinity at five levels 2, 4, 8, 16 and 20 dSm-1 for wheat and 0.7, 2, 4, 6 and 8 dSm-1 for bean and matric suction at four levels 2, 6, 10 and 33 kPa, on evaporation rate and redistribution of moisture and salinity in the soil profiles of sandy loam and clay loam. This study was conducted in greenhouse conditions in pots by compeletly randomized factorial desigh with 3 replicates.  It was found that evaporation rate decreased by time in the saline and water stress treatments, especially in the clay loam soils, and this reduction was more in the high suction and salinity levels. The lowest evaporation reduction was observed in treatments with the highest soil moisture content. Because, water availability reduced the salinity effect on evaporation. As, at the 2kPa matric suction, the evaporation rate was approximately the same at all levels of salinity and the highest throughout the day after treatment. In the 15th day after treatment and at the 33kPa suction, different salinity levels (from 0.7 to 20 dSm-1) reduced the evaporation rate by 19% in both soils. Also, the results showed that the ECe of the drained soils with 10kPa constant suction increased exponentially with moisture reduction. This trend was more in the clay loam soils. Because the evaporation/drainage ratio of the clay loam soil is more than the one in the sandy loam soil. The salinity redistribution in the both soil profiles and for the two plants were almost constant over time. Also, moisture reduction over the time was higher in the clay loam soil than the one in the sandy loam soil, especially under low salinities.

The effects of soil matric suction and salinity were investigated on the yield components and root development of the corps, wheat and bean within greenhouse conditions. The results showed that yield components and root dry weights of wheat and bean increased with increase in matric suction (from 2kPa) and reached their maximum values at suctions of 6-10 kPa. At suctions higher than 10kPa and under EC≤8dSm-1 for wheat vs. EC≤4dSm-1 for bean, all the yield components of wheat and bean (except for 1000-kernel weight) decreased, while under higher salinities, their values remained nearly the same. At suctions higher than 10kPa and under all salinity levels, 1000-kernel weights of wheat and bean remained nearly constant. The salinities of low to medium levels did not clearly affect yield and root development of either plant. Minimum root densities of wheat and bean occurred at suction 6kPa while at other points of suction (2, 10 and 33kPa), their values almost corresponded with each other. Salinity did not clearly affect wheat and bean root densities. Wheat shoot-root ratio decreased with matric suction (up to 10kPa) under EC≤8dSm-1, while under higher salinities, this ratio increased with suctions. At 10kPa suction, weight ratio values approached each other, then remained nearly constant at higher suctions. The results finally revealed that plant response to salinity stress depends on aeration conditions in the root zone and the deficit in soil aeration can amplify the salinity stress.

In this study the effects of soil matric suction (2−33 KPa) and salinity (EC: 0.7−8 dSm-1 for bean and 2−20 dSm-1 for wheat) on the wheat and bean nutrient concentrations in two sandy loam and clay loam soils at green house condition was considerd. The potassium concentration increased and sodium decreased with matric suction in both plants. The nitrogen and calcium concentrations of bean and wheat increased with matric suctions and reached their extreme values at suctions 6-10 KPa. Concentration of nitrogen reduced and concentration of calcium remained nearly constant at higher suctions. The maximum concentration of iron and zinc were at suction 2KPa in both plants. As matric suction increased from 2 to 6 KPa, iron and zinc decreased strongly and remained nearly constant at higher suctions in both soils. Salinity increased concentrations of iron and calcium and reduced concentration of potassium in both plants. While it did not affect concentrations of nitrogen, sodium and zinc. The low soil matric suctions amplified the salinity stress due to aeration deficit. Also comparing two plants showed that because of high sensitivity of bean to stresses, changes of its nutrient concentrations under different levels of salinity and matric suction were greater than wheat.

This study was conducted to investigate the effect of water salinity and sodicity on pore size distribution and plant-available water of two clay and sandy clay loam calcareous soils. All combinations of water EC values of 0. 5، 2، 4 and 8 dS m-1 and SAR values of 1، 5، 13 and 18 (in total 16 solutions) were used to wet and dry the soil samples for five cycles. Then، water retention of the soil cores was measured at matric suctions of 0 (θs)، 10 (θ10) 100 or 300 cm (θFC) and 15000 cm (θPWP). The following quantities were calculated: the difference between θ100 or θ300 and θ15000 considered as available water contrent، the θs and θ10 as macrorosity، the θ10 and θ100 as mesoporosity، and the θ100 as microrosity. The initial porosity of both soils was similar، but the greater values of pore indices and θFC، θPWP and AWC were measured in the clay soil due to clay swelling. As water EC increased، mesopores were destructed and altered to macropores and micropores. Salinity altered the mesopores into macropores due to contraction of diffuse double layer and particle’s flocculation and consequently decreased the θFC، and created new micropores which were responsible for the higher value of θPWP. These trends ultimately diminished the AWC. As water SAR increased، mesopores were destructed and altered to micropores but it did not significantly affect the macropores. With increment of SAR، both θFC and θPWP increased due to structural distruption clay swelling and dispersion resulting in increased adsorptive and interlayer surfaces. The increasing effect of SAR on θPWP was greater and more distinct so that AWC was reduced. As a result، high values of SAR of irrigation water decreased the soil available water to plants besides its toxicity and hazardous effect on plants. With increment of irrigation water salinity، the destructive impacts of SAR diminished. The influence of water quality on water retention was pronounced for the clay soil. ‎