بررسی اثر تغییر کاربری اراضی بر برخی خصوصیات فیزیکی و شیمیایی خاک و فرسایش‌ در مناطق خشک (مطالعه موردی: منطقه‌ی هیرمند سیستان)

هدف از اجرای این تحقیق، بررسی خصوصیات فیزیکی شیمیایی و فرسایش‌پذیری خاک در اراضی تغییر کاربری یافته ی منطقه ی سیستان است. برای اجرای این پژوهش تغییرات مکانی کاربری‌ اراضی براساس تصاویر ماهواره‌‌ای بررسی شد. با استفاده از تصاویر سنجنده‌های etm و oli ماهواره ی لندست مربوط به سال‌های 2001 و 2019، نقشه ی کاربری اراضی تهیه و نقشه تغییر کاربری یافته از مرتع به کشاورزی سیلابی و بایر مشخص و صحت‌سنجی شد. 10 نمونه خاک از هر کاربری‌ در قالب طرح بلوک تصادفی و از دو عمق 25 0 و 50 25 سانتی‌متر برداشت شد. یافته‌ها نشان داد که درصد رس، سیلت و شن در اراضی تغییر کاربری یافته از مرتع به کاربری‌های کشاورزی سیلابی و بایر تفاوت معنی‌دار داشته است (0.05 >p). در بررسی شاخص پایداری خاکدانه‌ها (dsa) نیز یافته‌ها نشان داد که مقادیر این شاخص در کاربر‌های کشاورزی سیلابی و بایر به ترتیب 34 و 45 درصد کاهش یافت. همچنین نتایج بیانگر کاهش به ترتیب 18 و 43 درصدی رطوبت خاک و افزایش معنی‌دار مقادیر وزن مخصوص ظاهری نسبت به کاربری مرتع بوده است. در بررسی خصوصیات شیمیایی خاک نیز یافته‌ها نشان داد که مقدار اسدیته، هدایت الکتریکی، نسبت جذب سدیم، سدیم و درصد آهک خاک در کاربری‌های کشاورزی سیلابی و بایر به طور معنی‌دار نسبت به کاربری مرتع، افزایش و در مقابل درصد مواد آلی و پتاسیم به طور محسوسی کاهش یافته است (0.05 >p). بر این اساس با توجه به نتایج به دست آمده از این تحقیق، تغییر کاربری اراضی به ایجاد محدودیت هایی در خصوصیات فیزیکی و شیمایی خاک منجر شده که چنین تغییراتی تخریب خاکدانه‌ها و افزایش فرسایش‌پذیری خاک را در این اراضی به همراه داشته است. با توجه به بحران های زیست محیطی موجود، اتخاذ برنامه‌های مدیریتی مناسب در بهره‌برداری اصولی از اراضی منطقه ی سیستان ضروری به نظر می رسد.

Investigating of land use change effect on some soil physical-chemistry characteristics and Erosion in arid areas (case study: Hirmand of sistan)

Extended abstract1 IntroductionThe landuse change is one of the critical worldwide issues that has caused a problem in natural resource sustainability. The dynamics of landuse and landcover change (LULC) affected by the anthropogenic activities and climate change in arid areas, were caused environmental degradation of these areas. This process has the negative effects on soil physicochemical properties. Soil degradation is the key component of land degradation that affected by landuse changes. So that it causes organic waste carbon, decreases the soil aggregate stability and structure and, consequently the raises of soil erodibility. So to understand the impacts related to these changes in landuse (LU), assessment of the effects of these changes on soil characteristics is important. Therefore, the current study aim was to investigate the effect of landuse change on physicochemical characteristics of soil and erosion in Sistan area.2 MethodologyThis research has done in Sistan area. This area laid southeastern border Iran and Afghanistan. The Sistan region forms a part of the DashteLut and hence an exhibits extreme arid climatic regime. The region is nearly flat and featureless arid plain with an average height of 465 -500m ASL in its eastern parts. In this study, at first spatial landuse changes in Sistan area determined. To achieve this purpose, used satellite images. By using the Landsat satellite images related to the years 2001 and 2019, the land use maps prepared, and by comparison approach in Idrisi Selva software, the map of landuse change was extraction. After that, the areas that converted from rangeland to floodagri and bare land determined and that accuracy were assessed. Infield operation, 60 soil samples were collected from tow depths 025 and 2550 cm in different landuse such as rangeland, floodagri, and bare land. The Samples were collected in a completely randomized block design. To study the physical properties of soil, by hydrometer method, by the soil texture, and by measuring the mean weight diameter (MWD), the geometric mean diameter (GMD) and dry stable aggregates (DSA), the aggregate stability was determined. Also, the soil moisture and bulk density were measured. To investigate the chemical characteristics, the soil properties such as organic carbon, acidity (PH), electrical conductivity (EC), sodium absorption ratio (SAR), CaCO3, Na, and available K and P measured in the soil laboratory. The soil erodibility index calculated five characteristics, including sand, silt with fine sand, organic matter, soil structure class, and the infiltration rate class of the soil profile. To analysis the mean of parameters among different land uses were used the Duncan test.3 Results The result of the study of physical properties showed that the percentages of sand, silt, and clay particles among the landuse that under study were significantly different. So that by the landuse change from rangeland to floodagri and bare land, the distribution of soil particle size differently, that consequently the soil texture has changed from loamsiltclay class in rangeland to lighter class loamsilt and loamsand in floodagri and bare land respectively. According to this change, the aggregate stability of soil inland converted from rangeland to floodagri, and bare land 34 and 45 percent have decreased. Also by landuse change, the soil moisture 18% and 43 % has decreased respectively. The results also showed that the bulk density of soil, acidity, electrical conductivity, Na, CaCO3 and absorption ratio (SAR), increased in converted landuse whereas, the organic carbon and available K soil, have decreased significantly. In addition, after landuse change, the erodibility index has increased significantly (P < 0.05). So that the amount of this index in floodagri and bare land compared to the rangeland landuse, more than equal 4 and 7 respectively. 4 Discussion Conclusions In this study, for the first time, has investigated the physicochemistry characteristics of soil and erodibility in land converted from rangeland in Sistan area. The results revealed that the conversion of natural rangeland to floodagri and bare land had negative effects on the measured soil properties. So that the percent of sand has increased, that changed the distribution of soil particle size, and according to that, the soil texture has changed also. This caused the aggregate stability soil to reduce. In addition, by decreasing the soil moisture, the plant growth has limited in this lands and given the high evaporation potential in Sistan area, the evaporation from land surface increased and according to that the electrical conductivity, acidity, Na and absorption ratio (SAR) in converted lands have increased, whereas, the organic carbon and available K soil, have decreased. This process has caused the Soil degradation, that affected by landuse changing. Therefore, the landuse change by destroying the soil structure and landcover in converted lands, cause increases the potential of erodibility, that given exist environmental crises in Sistan area, has required the suitable planning to principle productivity of lands in Sistan area.