تخمین منحنی رطوبتی تعدادی از خاک‌های شور و شور و سدیمی با استفاده از توابع انتقالی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری مهندسی علوم خاک دانشگاه تهران

2 دانشیار گروه مهندسی علوم خاک دانشگاه تهران

3 کارشناس ارشد پژوهشکده تحقیقات کشاورزی، پزشکی و صنعتی کرج

چکیده

حدود 20 میلیون هکتار از اراضی کشورمان را خاک­های مبتلا به نمک تشکیل می­دهد. هدف از این تحقیق اشتقاق توابع انتقالی تعدادی از خاک­های مبتلا به نمک جهت پیش­بینی پارامترهای معادله وان­گنوختن و رطوبت در مکش­های مختلف با استفاده از خصوصیات زودیافت خاک بود. به­ همین منظور 68 نمونه خاک از خاک­های جنوب تهران انتخاب گردید (خاک­های شور و شور و سدیمی). منحنی رطوبتی خاک­ها در پتانسیل­های ماتریک صفر، 10-، 33-، 100-، 300-، 500-، 1000- و 1500- کیلو پاسکال تعیین شدند. فراوانی نسبی ذرات خاک، جرم ویژه ظاهری، کربنات کلسیم، کربن­آلی، EC و SAR اندازه­گیری شده و پارامترهای معادله وان­گنوختن نیز با استفاده از نرم­افزار RETC بدست آمد. همچنین کارایی توابع بدست آمده در تخمین منحنی رطوبتی با تعدادی از توابعی که قبلاً توسط محققین مختلف ارائه شده بود (13 تابع) مقایسه گردید. بطورکلی یافته­های این پژوهش نشان داد: 1- با استفاده از توابع انتقالی می­توان نقاط مختلف منحنی رطوبتی خاک و پارامترهای معادله وان­گنوختن را به میزان قابل­قبولی تخمین زد (در توابع نقطه­ای: 577/0≤ R2Adj ≤ 844/0 و 0296/0 ≥ RMSE(cm3/cm3) ≥ 0121/0). 2- نتایج آنالیز حساسیت نشان داد که حساسیت اکثر توابع نقطه­ای به تغییرات جرم مخصوص ظاهری بیشتر از بقیه متغیرها بوده و نسبت رس به سیلت، EC و شن در مراتب بعدی قرار می­گیرند. 3- با توجه به ضریب پارامتر EC در معادلات و با توجه به ضرایب همبستگی جزئی و نتایج آنالیز حساسیت، مقادیر بالای پارامترEC می­تواند تا حدودی توزیع اندازه منافذ و نهایتاً شکل منحنی رطوبتی را بواسطه انبساط و انقباض تغییر داده و این تغییرات را می­توان با وارد کردن  متغیرهای EC و SAR در ایجاد توابع، تا حدودی لحاظ کرد. 4- مقایسه توابع قبلی ارائه­شده و توابع بدست آمده نشان می­دهد که توابع بدست آمده در این تحقیق، بهترین توابع در تخمین منحنی رطوبتی خاک­های مورد مطالعه می­باشند.

کلیدواژه‌ها

عنوان مقاله [English]

Estimation of Moisture Retention Curve in Some Saline and Saline-sodic Soils with Pedotransfer Functions

نویسندگان [English]

  • Naser Khaleghpanah 1
  • M. Shorafa 2
  • S. Teimouri 3
1 Ph.D. Student of Soil Science, University College of Agriculture and Natural Resource, University of Tehran, Karaj, Iran
2 Associate Professor of Soil Science Department, University College of Agriculture and Natural Resource, University of Tehran, Karaj, Iran
3 Master Of Science-Soil Science, Agricultural, Medical and Industrial Research School, Karaj, Iran
چکیده [English]

Salt-affected soils cover up to 20 million hectares of our country. The objective of this study was to derive PTFs of some salt-affected soils to predict the parameters of van Genuchten equation and water retention at a pre-defined potential from readily/easily obtainable soil characteristics. For this purpose, 68 soil samples were chosen from south part of Tehran (saline and saline-sodic soils). Moisture retention curve for these samples were determined at matric potential of 0, -10, -33, -100, -300, -500, -1000 and -1500 kPa. Particle size distribution, calcium carbonate, bulk density, organic carbon, EC and SAR were measured and RETC program was used to obtain the Van Genuchten equation parameters. As to the EC and SAR effect on pore size distribution of soil, these parameters were used in pedotransfer functions as predictor parameters. Also, performance of derived functions in estimation of moisture retention curve was compared with a number of functions (13 functions) that previously were provided by different researchers. Generally, the result of this study showed: 1- Water retention at a pre-defined potential and parameters of van Genuchten equation can be estimated by pedotransfer functions with reasonable accuracy (point transfer functions: 0.844 ≤ R2Adj ≤ 0.577 and 0.0296 ≤ RMSE(cm3/cm3) ≤ 0.0121), 2- Sensitivity analysis results showed that the sensitivity of most point functions to changes in bulk density was more than the rest of the parameters and clay-silt ratio, EC, and sand were at the next levels,  3- Considering the coefficient of EC in the equations, partial coefficients of correlation, and results of sensitivity analysis, higher amounts of EC could somewhat affect pore size distribution and, consequently, the shape of moisture retention curve of the soils. This change, which is caused by swelling and shrinkage, to some extent can be predicted via introduction of EC and SAR parameters in developing the equations,4- Comparison of previous functions with those obtained in this study show that derived functions in this research are the best functions for estimation of soil moisture retention curve.

کلیدواژه‌ها [English]

  • Pedotransfer functions
  • van Genuchten parameters
  • Soil moisture retention curve
  • Saline soils
  • Saline-Sodic soils

مراجع

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پژوهش های خاک
دوره 26، شماره 4
اردیبهشت 1391
صفحه 391-402

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