فاطمه ولی زاده کاخکی

Fire is a big threat to natural resources in the world and is an important factor in changing the physical and chemical characteristics of the soil. The purpose of this study was to investigate the effect of fire on the physical and chemical properties of the soil in oak forest of Badreh located in 70 km of Ilam province and to compare it with unburnt (control) areas. Soil sampling carried out in two topsoil (0-5cm) and subsoil (5-20cm) depths. Five plots in 50×50m dimension designed in burnt and unburnt forests and in each plot 5 soil samples were collected randomly from topsoil and subsoil and were transferred to the laboratory to soil physical and chemical analyses. According to the results fire increased the amount of sand and silt by 15.56%, 15.18% respectively, compared with unburnt forest. But, the percentage of clay decreased under burn condition. Fire declined aggregate stability in soil 0-5 and 5-20cm depths by 10.61 and 17.81 respectively. The most CEC content (20.98 cmol/kg) and the least one (16.56 cmol/kg) was observed in unburnt forest comparison with burnt forest respectively. Burned increased soil organic carbon but by increasing soil depth decreased it. In the study area, fire affected significantly K and P available in forest soil. To sum up, fire changed soil physical and chemical properties of oak forest in Badreh region in Ilam Province as well as this phenomenon increased essential nutrient elements resulting from soil fertility improvement in the study area.

Among the soil forming factors, climate by effect on weathering severity and parent material degradation plays a basic role on soil evolution. In order to investigate the effects of climate on soil physicochemical properties and evolution in Ilam province, two regions from a climosequence were selected. The purpose of this study was to compare soil evolution in a climosequence according to the soil indices of clay, iron, aluminum, manganese, and 5 profiles in each land units of Salehabad and Ilam plains were dug, described and sampled. The results of physicochemical analysis of Salehabad and Ilam soil profiles in two regions were different and significant difference were observed within the all parameters except pH and silt. In addition, electrical conductivity increases in Salehabad soils with ustic moisture regime and hyperthermic temperature regime comparing to Ilam soils with xeric moisture and thermic temperature regimes revealed the climate effect on them and changes in soil orders from Inceptisols in Salehabad to Mollisols in Ilam were related to the changes in moisture and temperature regimes. Soil classification showed that Salehabad soils were placed in Gypsic Haplustepts and Ilam soils were placed in Gypsic Calciusteps, Typic Calcixerolls and Typic Haploxerolls subgrops. Based on obtained results the iron, aluminum and manganese amounts in Ilam soil profiles were higher than those in Salehabad ones and less weathering in Salehabad region were happened by drier climate, lower humidity and higher temperature. Additionally, the results showed that the horizons with gypsum did not have potential to store clay and metal oxides, and the soil evolution according to the distribution and amount of iron, aluminum and manganese offered a better understanding of the soils and their forming conditions and the Ilam soils showed further evolution.

Fire is a major threat for natural resources in the world and is an important factor in changing physical and chemical properties of soil. Knowledge of the positive or negative effects of fire on soil properties can be a great importance for the management of natural resources. This study was conducted with the aim of the effect of fire on physical and chemical properties of soil in rangelands of Badreh area in Ilam provice and comparison with non-fire areas (control). After field studies in Badreh area in the eastern of Ilam province, soil samples were taken from 0-5 and 5- 20cm depths and collected randomly and transferred to the laboratory. Physical analysis (soil texture, mean weight aggregate diameter, saturation moisture and bulk density) and chemical (organic matter, total nitrogen, phosphorus available, potassium available, calcium and magnesium exchangeable, cation exchange capacity) were carried out on soil samples. The highest amount of sand (46.4%) and soil silt (24.4%) were found in burned pasture and the highest clay content (39%) was found in control rangelands. Fire decreased the stability of aggregates and soil porosity in burned rangelands compared to unprocessed rangelands (14.28 and 8.68%) significantly (α= 0.05). The bulk density of the burned pasture was 9.1% higher than that of the control pasture. In the soil surface layer, the soil moisture content increased 16.98% compared to the control treatment. The fire decreased the amount of soil organic matter from 2.66% in control pasture to 2.19% in burned pasture (α= 0.05). Soil acidity increased significantly in burned pasture (pH=7.45) compared to control pasture (pH=7.07). The highest cation exchange capacity (24.82 cmol kg-1) and the lowest (18.98 cmol kg-1) were obtained in control and burned rangelands respectively. Also, with an increase in soil depth, the cation exchange capacity of soil decreased to 14.10%. The most available phosphorus, magnesium and calcium were obtained in burned pasture at the soil surface. Fire had no significant effect in the subsoil layer, on the amount of soil phosphorus, magnesium and calcium exchangeable. In general, the results indicate that fire in rangelands of Badreh area in Ilam province affected physical and chemical properties of soil. In most cases, soil quality is decreased chemically (decreasing organic matter, nitrogen, cation exchange capacity) and physically (soil texture changing, soil aggregate stability, porosity and bulk density), and in some cases, fire caused to release the nutrient elements such as phosphorus, calcium and magnesium in the soil and improved the nutrient cycling nutrients in the soil.