كليدواژه :
دشتسر پوشيده , دشتسر اپانداژ , دشتسر لخت , فرسايش بادي , فرسايش پذيري
چكيده فارسي :
فرسايش بادي وسعتي بالغ‌بر 20 ميليون هكتار از كشور پهناور ايران را در متأثر ساخته است. هفت ميليون هكتار از مناطق تحت تأثير فرسايش بادي كانون‌هاي بحراني ناميده مي شود كه كانون‌هاي جمعيتي، اراضي كشاورزي و مناطق صنعتي را در برمي‌گيرد. فرسايش پذيري خاك از مهم‌ترين شاخص هاي نشان‌دهنده پتانسيل فرسايش بادي در يك منطقه است. اين شاخص بستگي به ويژگي‌هاي فيزيكي و شيميايي ذاتي خاك دارد. منطقه موردمطالعه حوضه دشت يزد – اردكان كه در بخش شمالي استان يزد قرار دارد و در فلات مركزي ايران گسترده شده است. به منظور بررسي پتانسيل فرسايش پذيري بادي خشكه رودها و مجاور آنها 83 نمونه خاك در كف و بستر خشكه رودها و مجاور آنها در سه نوع دشتسر لخت، اپانداژ و پوشيده برداشته شد و برروي نمونه ها به منظور محاسبه مقدار فرسايش پذيري آزمايشات فيزيكي و شيميايي خاك صورت گرفت. مقدار فرسايش پذيري به دو روش دلگيلويچ و همكاران (1973)، مدل (1) و عظيمزاده و همكاران (1380)، مدل (2) بر حسب ton/ha-hr محاسبه شد. نتايج نشان داد كه هر دو مدل در اراضي دشت سر پوشيده با بافت ريزدانه خاك از نوع Loam و Clay Loam مقدار فرسايش پذيري را متوسط تا زياد پيش بيني كرد و در اراضي دشت سرهاي لخت و اپانداژ كه درصد پوشش سنگ فرش متوسط تا زياد مي باشد، در مدل (1) مقدار فرسايش پذيري را در بعضي نقاط كم و در بعضي نقاط ديگر متوسط تا زياد به دست آمد ولي در مدل (2) با در نظر گرفتن پوشش سن گفرش در تمامي نقاط دشتسرهاي لخت و اپانداژ كم بدست آمد. مدل (1) بدون در نظر گرفتن رخساره هاي مختلف ژئومورفولوژي، بيشتر در مورد بررسي ميزان فرسايش پذيري بادي خاك در اراضي كشاورزي و دشت رسي با بافت ريزدانه خاك مناسب است و برآورد مقدار فرسايش پذيري را در قسمت مياني منطقه در مقايسه با مدل (2) به‌درستي پيش بيني كرد. به‌منظور سهولت و كاهش دادن زمان و هزينه به‌منظور محاسبه فرسايش پذيري، مدل (1) در اراضي بافت ريزدانه و كشاورزي و بدون سنگ فرش شامل دشت سر پوشيده توصيه مي شود. مدل (2) در دشتسرهاي لخت و اپانداژ كه داراي پوشش سنگ فرش متوسط تا زيادي هستند، مدل مناسبي است و به‌منظور دقيق تر محاسبه فرسايش پذيري در دشت سر پوشيده علاوه بر پارامتر فيزيكي خاك، پارامترهاي شيميايي خاك هم كه در عامل فرسايش پذيري دخالت دارند، مدل (2) مناسب مي باشد. به‌منظور كاهش فرسايش پذيري در دشت سرهاي لخت و اپانداژ باوجود درصد سنگ فرش متوسط تا زياد توصيه مي شود هيچ‌گونه دست كاري بر روي پوشش سنگ فرش انجام نشود و در دشت سر پوشيده اقداماتي نظير احداث بادشكن در اراضي كشاورزي و مالچ پاشي بر روي تپه هاي ماسه اي انجام شود.
چكيده لاتين :
Introduction
Wind erosion is a serious problem throughout the world. Wind erosion is due to the increase wind velocity and air turbulent. This phenomenon usually is seen in soft, smooth, bare, dry, disperse and fine soil. It always classifies to two main factors named erodibility and erosivity. The first depends on the physical and chemical properties of soil and the second depends on wind physic and kinetic energy.
The aim of this study is estimating the potential soil wind erodibility in oueds and adjacent from them in coarse and medium grain plain and in fines and agricultural lands located in fine grain plain presented using two models. The first model based on percentage of particles larger than 0.84 millimeter in soils and the second model based on soil physical and chemical properties in study area.
Methodology
The case study is Yazd-Ardakan plain is located in north of Yazd province. Which is geographical location in the northern latitude 31 degrees 48 minutes and 32 degrees 13 minutes and eastern longitude 52 degrees 57 minutes and 54 degrees 59 minutes and has been widespread in the central plateau of Iran. In the case study, 83 soil samples were taken in 3 pediment including coarse grain plain, medium grain plain and fine grain plain in depth of 0-20 cm. Most of the samples were in oueds with high density and adjacent from them. some samples were in fines and agricultural lands in fine grain plain. To evaluate the potential soil wind erodibility in ton/ha-hr with Dolgelivich et al. method, it was calculated with percent of soil particle more than >0.84 millimeter and with Azimzadeh et.al.’s method, the potential soil wind erodibility was measured with physical and chemical soil parameters including: percent of pavement (reg), mean diameter (d50), Electrical Conductivity (EC), Sodium Absorb Ratio (SAR).
Results and Discussion
In 83 soil samples, the most soil texture was Sandy Loam which means that the area has the most percent of sand content. pavement was measured in range of 30 to 80 percent in coarse and medium grain plain and zero to 5 percent were variable in fine grain plain. The maximum amount of mean diameter was in range of 0.06 to 0.07 millimeter and the most percent of soil particle >0.84 millimeter was in range of 3.6 to 4. The amount of EC was variable from 1.5 to 6 dS/m and SAR was in range of 5.3 to 125.6 wich means soils in study area in terms of salinity were low to medium and in terms of alkali were medium to high. The amount of soil erodibility with model (1) was obtained in range of 30 to 36.98 ton/ha-hr and in model (2) was obtained in range of 0.04 to 80 ton/ha-hr. Both two models in fine grain plain with fine textured soil any kind of Loam and Clay Loam were estimated the amount of soil erodibility from medium to high and in coarse and medium grain plain lands which have medium to high desert pavement, in model (1) the amount of soil erodibility obtained low in some points and were high in the other points. But in model (2) with considering the percentage of desert pavement in all of the points in coarse and medium grain plain, the amount of soil erodibility obtained low. Model (1) without considering the geomorphological facies, is more useful and appropriate in agricultural and clayey plain lands and estimated properly the amount of soil erodibility in central of study area in comparison with model 2. In order to lower the time and cost to estimate the amount of soil erodibility in fine texture soils and agricultural lands located in fine grain plain, model (1) recommended. Model (2) is appropriate in coarse and medium grain plain which have medium to high desert pavement and in order to calculate more exactly the amount of soil erodibility in fine grain plain, in addition to soil physical parameters, soil chemical parameters that involve in soil erodibility factor, model (2) is appropriate.
Conclusion
Soil erodibility is an important issue in areas which were vulnerable to wind erosion. In clay and agricultural lands and some areas with sand dunes located in fine grain plain, we must have use some ways for lowering soil erodibility and controlling wind erosion for example making wind breaks surrounding agricultural lands and sprinkle mulch on sand dunes. In some areas which have low to high desert pavement, soil erodibility is low and any manipulation in the area is not recommended.
