نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری گروه علوم خاک دانشکده کشاورزی، دانشگاه صنعتی اصفهان

2 دانشیار گروه علوم خاک، دانشکده کشاورزی، دانشگاه صنعتی اصفهان

3 استاد گروه علوم خاک، دانشکده کشاورزی، دانشگاه صنعتی اصفهان

چکیده

هدایت هیدرولیکی اشباع (Ks) خاک یکی از ویژگی­های ضروری برای مدیریت پروژه­های آبیاری، مدل­سازی حرکت آب و املاح و پیش­بینی توابع هدایت هیدرولیکی غیراشباع خاک می­باشد. اندازه­گیری Ks، به ویژه در مقیاس بزرگ در آزمایشگاه و مزرعه زمان­بر و پرهزینه است. از طرفی Ks تحت تأثیر عوامل مختلف دارای تغییرات مکانی و زمانی زیادی می­باشد. بنابراین پیش­بینی و مدل­سازی آن­ توسط توابع انتقالی خاک برای بسیاری از پژوهش­ها می­تواند مفید باشد. این پژوهش در بخشی از شهرستان­های کوهرنگ و فارسان واقع در استان چهارمحال و بختیاری با هدف ارزیابی کارایی برخی توابع انتقالی موجود در منابع و استخراج توابع انتقالی جدید (PTFs) برای برآورد Ks انجام گرفت. نمونه­های دست­نخورده به حجم cm3100 از خاک سطحی در 100 نقطه که توزیع مناسب و یکنواختی در منطقه و در کاربری‌های مختلف داشتند، برداشت شد. ضریب Ks به روش بار ثابت برای این نمونه­های دست­نخورده در آزمایشگاه اندازه­گیری شد. برخی ویژگی­های زودیافت خاک نیز اندازه­گیری شده و PTFs برای برآورد Ks به روش رگرسیون چندمتغیره گام به گام استخراج شد. هم­چنین مقادیر Ks اندازه­گیری­شده با برآورد PTFs موجود در منابع مقایسه شد. نتایج نشان داد که PTFs موجود در منابع قادر به برآورد مناسب Ks در منطقه نیستند. در بین توابع انتقالی بررسی‌شده موجود در منابع، مدل توانمند شبکه عصبی Rosetta (SSC+BD) بهترین بود. ناکارآمدترین PTFs برای برآورد Ks در خاک­های مورد بررسی مربوط به مدل­های رگرسیونی براکینز و همکاران (1984) بود. بـهر حـال PTFs استخـراج­شـده بـرای منطقـه بهتر از PTFs موجـود در منابــع توانسـت Ks را بـرآورد کنند (52%R2=،‌‌mmh-15/0RMSE =). یافته­ها نشان داد که لگاریتم Ks با چگالی ظاهری نسبی (تراکم نسبی)، چگالی ظاهری مؤثر، نسبت درصد رس به کربنات کلسیم (Clay/CaCO3)، نسبت درصد کربنات کلسیم به ماده آلی (CaCO3/OM) و لگاریتم برهم­کنش چگالی ظاهری و درصد رس (ln(BD×Clay)) هم­بستگی منفی دارد و با OM، لگاریتم نسبت OM/Clay، درصد شن خیلی ریز و تخلخل خاک هم­بستگی مثبت دارد. چون خاک­های مورد بررسی دارای ساختمان نسبتاً خوبی بودند و در استخراج PTFs ویژگی­های ساختمانی نقش بیش­تری داشتند، پیشنهاد می­شود در آینده برای پیش­بینی بهتر Ks خاک­ها در این منطقه برخی ویژگی­های ساختمانی دیگری مانند میانگین قطر خاک­دانه­ها به عنوان تخمین­گر مد نظر قرار گیرد.

کلیدواژه‌ها

عنوان مقاله [English]

Evaluating and Developing Pedotransfer Functions to Predict Soil Saturated Hydraulic Conductivity at Landscape Scale in Central Zagros

نویسندگان [English]

  • Hamid Kelishadi 1
  • Mohammad Reza Mosaddeghi 2
  • Mohammad Ali Hajabbasi 3
  • Shamsollah Ayoubi 2

1 PhD Student, Department of Soil Science, College of Agriculture, Isfahan University of Technology, Isfahan, Iran

2 Department of Soil Science, College of Agriculture, Isfahan University of Technology, Isfahan, Iran

3 Department of Soil Science, College of Agriculture, Isfahan University of Technology, Isfahan, Iran

چکیده [English]

Soil saturated hydraulic conductivity (Ks) is an essential property in managing irrigation projects, water and solute transport modeling and for predicting unsaturated hydraulic conductivity functions. Laboratory and field measurements of Ks are time-consuming and costly especially in the large scales. Moreover, Ks is affected by different factors and thus its predicting and modeling by derived pedotrasfer functions (PTFs) or those in the literature can be useful for many purposes. This study was performedto evaluate the already existed in literature and derived PTFs for predicting Ks in Farsan and Koohrang regions, Chaharmahal-va-Bakhtiari province in the central Zagros. Undisturbed samples (volume of 100 cm3) were collected from the surface soil at 100 locations which were well distributed in the region and in different land uses. The Ks of the undisturbed samples was measured using the constant-head method in laboratory. Easily-available soil properties were also determined and PTFs for Ks prediction were derived by multiple stepwise regression. The measured Ks values were also compared with the predictions of several PTFs in the literature. Results showed that PTFs in the literature could not accurately predict the Ks in the region. Among the literature PTFs, powerful neural network model of Rosetta (SCC+BD) was the best. The worse PTFs for Ks prediction in the studied structured soils were Brakensiek et al. (1984) PTFs. However, the derived PTFs predicted the Ks in the region better (R2=52%, RMSE=0.5 mm/h) than the literature PTFs. The findings revealed that logarithm of Ks negatively correlates with relative bulk density (relative compaction), effective bulk density, clay to carbonate content (Clay/CaCO3) and carbonate to organic matter content (CaCO3/OM) ratios and bulk density and clay interaction [ln (BD×Clay)] and has positive correlations with OM, ln(OM/Clay), very fine sand content and soil porosity. The studied soils had good structure and the structural properties had significant role in the derived PTFs. Therefore, it is suggested to include additional structural properties such as aggregates' mean diameter as a predictor for better Ks prediction in future.

کلیدواژه‌ها [English]

  • Pedotransfer functions
  • saturated hydraulic conductivity
  • relative compaction
  • effective bulk density
  • Central Zagros
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