مقایسه سامانه های رده بندی جهانی و آمریکایی برای طبقه بندی خاک های متکامل دارای افق تجمع رس تراس های رودخانه ای زاینده رود

با توجه به ارتباط چندجانبه خاک و سایر اجزاء سیستم های سطحی زمین، رده بندی خاک ابزاری ضروری در جهت پهنه بندی صحیح و اتخاذ تصمیمات مدیریتی در عرصه های منابع طبیعی می باشد. به منظور بررسی توانایی دو سامانه طبقه بندی جهانی و رده بندی آمریکایی در توصیف تغییرپذیری های جزئی موجود بین خاک های متکامل (دارای افق تجمع رس) تراس بالایی رودخانه زاینده رود، این پژوهش در سطح مطالعاتی نیمه تفضیلی طراحی و پس از انتخاب چهار خاکرخ شاهد، کلاس بندی خاک طبق الگوی دو سامانه انجام گرفت. نتایج نشان داد که سامانه طبقه بندی جهانی به دلیل مزایایی چون توصیف کننده های clayic، cutanic، ochric، ruptic، endocalcaric و نیاز به داده های آزمایشگاهی کم تر، در توصیف ویژگی های درون خاک رخی در این پژوهش بسیار موفق تر از سیستم رده بندی آمریکایی بوده، اما همچنان توانایی نمایش تفاوت در توالی افق های مشخصه تمامی خاک رخ های موجود در این مطالعه نیمه تفضیلی را نداشته است. از طرف دیگر سامانه آمریکایی بر خلاف الگوی جهانی، با بهره گیری از رژیم رطوبتی و حرارتی خاک، توصیفی از شرایط محیطی ارائه نموده است و اسم خاک در این سامانه نشان دهنده وجود خاک با افق آرجیلیک در شرایط اقلیمی خشک بوده است. بنایراین می توان بیان نمود که میزان کارآیی هر یک از سامانه های طبقه بندی جهانی و آمریکایی بسته به نوع هدف بکارگیری و مقیاس مطالعه متفاوت خواهد بود.

Appraisal of The World Reference Base for Soils (WRB) and US Soil Taxonomy for Classification of Developed Soils of Zayandehrud River’s upper Terrace

Introduction: Sustainable management of natural resources is one of the main goals of land use planning and is quite complicated due to various interactions in any given ecosystem. Therefore soil as the bed for interactions of main ecosystem components can be a good indicator candidate as the main requirements of sustainable land use management. Soil classification is a valuable technique for transferring a large set of data along with soil history and is a necessary tool for zoning and soil management plans. This indicates efficiency and potential of classification for showing inner and outer soil properties and stimulating for achieving the best possible soil classification system. Among various existing soil classifications, the  World Reference Base for Soil Resources (WRB)  as an international  soil classification  system and USDA Soil Taxonomy (STus) are more globally accepted and applied. In both systems soil orders are similar and their classifications are based on acceptable rules. However each one of them has its own characteristics and reflects its potentials. Also the relationship between soil and landscape and the necessity of sustainable nature management convert soil classification to a tool which is essential for appropriate management decisions about utilization and conservation of natural resources. This study was conducted to investigate the efficiency of Soil Taxonomy and WRB for classification of developed soils of Zayandehrud River’s upper terrace.;Materials and Methods: This study applied on the current pathway of Zayandehrud River.  Several pedons were studied in a semidetailed scale study. Finally, four different pedons were selected. Routine physical and chemical analyses Selected physicochemical properties of the soil samples were determined according to the Soil Survey Laboratory Manual and soils were classified according to Soil Taxonomy (2014) and WRB (2015) systems. Argillic (Argic), and Cambic diagnostic horizons were investigated after field and laboratory work.;Results: Based on both field and lab studies, for these soil pedons due to lithologic discontinuity, presence or absence of Cambic horizon and accumulated clay horizon, four different sequence of horizons are realizable. Calceric matrix of soil pedons is also another prominent property of them. Due to aridity condition of the region and presence of Argilic horizon based on STus, all soil pedons were classified in great group of Haplargids. According to WRB, all pedons considered as reference group of Luvisols. As the results show, the difference between these two systems of classification was originated at family level for STus and qualifiers for WRB. In fact the difference is due to environmental qualifiers and intrinsic soil profile propertie. STus is performing better than WRB indefining the environmental conditions. Such pattern reflects the climate conditions in any given soil name. Moisture regime (Aridic) at order level (Argids) and temperature conditions (Thermic) at family level have been realized for all soil pedons. However WRB not only at first level but also for second level of classification (qualifiers) was not able to indicate. On the other hand this study results showed that main qualifiers have enhanced WRB efficiency compared to STus and was also able to define the variety of horizon sequences. STus did not show such potential even at family level and all four soils were classified under one name.;Based on the findings of the research, using qualifiers and little laboratory data requirement by WRB caused this system to be more successful than Soil Taxonomy to describe internal attributes in the pedons. WRB was more flexible in reflecting described properties in soil nomenclature. But WRB was not able to reflect soil variability in this semidetailed study, completely. Also results showed that Soil Taxonomy couldcharacterize environmental properties of soils using soil moisture and temperature regimes. On the other hand, the presence or absence of Cambic diagnostic horizon in the four pedons can indicate a difference in their evolutionary pathway, but the presence or absence of Cambic horizon has been disregard in the names of both systems.;Conclusion: The efficiency of each system is vary according to the aims of soil survey, and both systems have advantages and disadvantages in relation to displaying the internal features and the soil environment. The WRB was more succeed than STUS in displaying variety of the characteristics of developed soils in this study, due to its advantages such as Clayic, Cutanic, Ochric, Ruptic, Endocalcaric and also requires less laboratory data. On the other hands, WRB is facing a serious challenge to management objectives related to climatic conditions and vegetation. Therefore, it can be concluded that purpose and scale of a study affects the efficiency of Soil Taxonomy and WRB classification systems to describe soil properties.;