شناسايي و پهنه بندي خصوصيات فيزيكي و شيميايي خاك با استفاده از روش هاي زمين آماري در GIS (مورد مطالعاتي: منطقه ميانكنگي؛ سيستان)

Survey and Zoning of Soil Physical and Chemical Properties Using Geostatistical Methods in GIS (Case Study: Miankangi Region in Sistan)

دسترسی به اطلاعات دقیق تغییرات مكانی خصوصیات خاك، به منظور فراهم نمودن پایگاه داده‎ای در راستای مدیریت پایدار خاك، همچون كاربرد نسبت مناسب كودها، بسیار ضروری است. به این منظور در زمستان سال 1391 تعداد 189 نمونه خاك دست نخورده از عمق 0- 30 سانتی‌متری سطح منطقه میانكنگی دشت سیستان به صورت شبكه‌بندی منظم با فواصل 500 متر جمع آوری و خصوصیات فیزیكوشیمیایی آن ها مورد مطالعه قرار گرفت. نرمال سازی داده‌ها صورت گرفت و مدل‏های نیم‌تغییرنما كروی، نمایی و كی‏-‏ بسل به عنوان بهترین مدل برازش برای نتایج آزمایش بدست آمد. در نهایت بر اساس پارامتر میانگین مجذور مربعات خطا روش كوكریجینگ جهت تولید نقشه‌های اسیدیته خاك و هدایت الكتریكی با متغیر كمكی درصد رس، درصد رطوبت اشباع و كربنات كلسیم با متغیر كمكی سیلت و محتوای ذرات رس با متغیر كمكی هدایت الكتریكی مورد استفاده قرار گرفت. همچنین نقشه‌های محتوای ذرات سیلت و شن به روش كریجینگ گسسته تولید شد. هدایت الكتریكی خاك‏های منطقه با ضریب تغییرات 99/102، دامنه تأثیر كم (935 متر)، تغییرات مكانی بسیار شدیدی داشت كه بیشتر متأثر از نوع خاك منطقه می‌باشد. همچنین، تجمع بالای مواد محلول در خاك منطقه، حاكی از گسترش هر چه بیشتر شوری در اراضی فاریاب منطقه مورد مطالعه تحت تأثیر آبیاری و كوددهی می‌باشد كه كاهش كیفیت و سلامت خاك را در پی داشته و نیازمند مدیریت صحیح و اجرای برنامه‌های هدفمند پیشگیری و مرتفع ساختن مسأله شوری در راستای بهبود كیفیت خاك و تحقق توسعه كشاورزی پایدار در این منطقه می‌باشد.

Introduction: In order to provide a database, it is essential having access to accurate information on soil spatial variation for soil sustainable management such as proper application of fertilizers. Spatial variations in soil properties are common but it is important for understanding these changes, particularly in agricultural lands for careful planning and land management. Materials and Methods: To this end, in winter 1391, 189 undisturbed soil samples (0-30 cm depth) in a regular lattice with a spacing of 500 m were gathered from the surface of Miankangi land, Sistan plain, and their physical and chemical properties were studied. The land area of the region is about 4,500 hectares; the average elevation of studied area is 489.2 meters above sea level with different land uses. Soil texture was measured by the hydrometer methods (11), Also EC and pH (39), calcium carbonate equivalent (37) and the saturation percentage of soils were determined. Kriging, Co-Kriging, Inverse Distance Weighting and Local Polynomial Interpolation techniques were evaluated to produce a soil characteristics map of the study area zoning and to select the best geostatistical methods. Cross-validation techniques and Root Mean Square Error (RMSE) were used. Results and Discussion: Normalized test results showed that all of the soil properties except calcium carbonate and soil clay content had normal distribution. In addition, the results of correlation test showed that the soil saturation percentage was positively correlated with silt content (r=0.43 and p <0.01) and negatively correlated with sand content (r=0.48 and p <0.01). In addition the soil saturation percentage with clay and soil electrical conductivity of the study also showed a positive relationship at the level of one percent of the electrical conductivity of clay particles had positively correlated (r=0.51 and p <0.01). Spherical, exponential and k-Bessel models were selected as the best models which fit the experimental results. In the case of spatial correlation between soil electrical conductivity characteristics of the region (with the range of 935 meter), and the maximum effective range was less than other soil properties that the reflect the same conditions and heterogeneous, the spatial distribution the features are. The effective range of pH, soil saturation percentage, calcium carbonate, clay, sand and silt contents were calculated 2346, 5953, 3806, 3608, 2123 and 1083 meters respectively. Spherical semivariogram (for a silt content), exponential (for electrical conductivity, soil moisture, sand, acidity) and K-Bessel (to clay) models werr obtained as the best models for studied soil characteristics. Finally, maps of electrical conductivity and pH with clay as covariate, saturated moisture percent and calcium carbonate equivalent with silt as covariate and clay particles content with electrical conductivity as covariate were produced with Co-Kriging method based on the parameter of mean squared error. Also maps of silt and sand particles content with the Disjunctive Kriging were produced. Conclusions: According to the produced maps soil electrical conductivity with coefficient of variation of 102.99 and low effective range (935 meter) showed a very high spatial variability which mostly depended on the soil type of Miankangi region. The content of calcium carbonate with an average of 18.66 percentage a relatively high figure and indicates calcium carbonate precipitation as one of the most soluble salts in the soil.Miankangi soils acidity in the neutral range (8.13) is alkaline. That is due to very low coefficient of variation obtained for pH, alkalinity of soil can be seen from its inherent feature. In addition, the high concentration of dissolved substances in studied soils represents further expansion of salinity in irrigated lands in the study area, which leads to reduce in soil quality and health due to irrigation and fertilization. Accordingly, it needs a proper management, implementation of targeted programs for prevention, and overcoming the salinity problems for the sake of improving the soil quality, as well as, achieving sustainable agricultural development in this region.