Document Type : Research Paper

Authors

• Mahyar Moshtaghi ¹
• hasan ramezanpour ²
• Nafiseh Yaghmaeian Mahabadi ²
• Mahmoud Shabanpour ³

¹ Ph.D. Student, Department of Soil Science, College of Agriculture, University of Guilan, Guilan, Iran.

² Associate Professor, Department of Soil Science, College of Agricultural Science, University of Guilan, Guilan, Iran.

³ Associate Professor Department of Soil Science, College of Agricultural Science, University of Guilan, Guilan, Iran.

Abstract

Introduction: Soil classification categorizes soils into different classes on the basis of their distinguishing characteristics and provides a structured conceptual framework for describing and understanding soil properties. There are two soil classification schemes that are generally regarded as having worldwide application, the Soil Taxonomy (ST) and the World Reference Base (WRB) which are also popular in Iran. These systems of classification consider diagnostic horizons and factors of soil formation as the basis of classification. The aim of this study was to determine the classification of soils of tobacco farms in the Talesh County of Guilan Province based on ST (2022) and WRB (2022) according to the soil diagnostic characteristics, then comparing two systems for soils of tobacco farms to determine the ability of better description of soils by these two systems of soil classification.
Materials and Methods: Talesh County is considered to be the most important tobacco production areas in Guilan Province and IRAN. The most extensive area of tobacco cultivation in Guilan Province is located in this County and in Jokundan and Mountain districts. The study area has a humid climate with cold winter and hot summer. The mean annual temperature is between 15.6 and 17.2 degrees Celsius and the annual rainfall is between 786 and 1370 mm. Based on the map of moisture and temperature regimes of Iran  and with the help of jNSM software, the moisture and temperature regimes were determined as Udic and the Thermic respectively. In the study area twenty pedons (eight pedons for Mountain and twelve pedons for Jokandan) were described and the morphological characteristics of the pedons layers were studied in the field according to the Soil Survey Manual. Then, the soil of each horizon was collected, air-dried, and sieved by passing through a 2 mm sieve before analyzing the properties of the soil. Soil pH, Electrical Conductivity, Texture, Organic Carbon, Calcium Carbonate Equivalent, Cation Exchange Capacity and Base Saturation were determined in all the samples according to Methods of Soil Analysis. Soils were then classified according to classification criteria of ST (2022) and WRB (2022) systems. For showing changes of tobacco farms soils, eleven pedons were selected as representative pedons and the reference between ST (2022) and WRB (2022) was established for tobacco soils at the level of the subgroup or secondary classification unit.
Results and Discussion: The results revealed that according to ST (2022), representative pedons of Mountain district were classified as Entisols, Inceptisols and Mollisols orders while, Jokandan had Entisols, Inceptisols, Mollisols and Vertisols pedons. WRB (2022) Reference Soil Groups (RSGs) for Mountain was Regosols, Umbrisols and Phaeozems and for Jokandan district were Fluvisols, Cambisols, Phaeozems and Vertisols. At lower levels of classification, ST (2022) uses climatic data as soil moisture regime whereas WRB (2022) does not use. Therefore, the suborders or great groups of all soils were separated based on the Udic moisture regime. Finally, representative pedons were classified as Typic Udorthents, Mollic Udifluvents, Oxyaquic Udifluvents, Typic Humudepts, Dystric Eutrudepts, Typic Hapludolls, Fluventic Hapludolls, Aquic Argiudolls, Typic Argiudolls and Aquic Hapluderts at great group level.
In regard to the WRB (2022), in the secondary levels, each section had its own series of principal and supplementary qualifications. Among those, the principal qualifications were mainly Eutric, Cambic and so on, and the supplementary qualifications were mainly Clayic, Loamic, Siltic, Humic and so on.
Conclusion: It was found that when compared with ST (2022), the WRB (2022) had stronger abilities to distinguish soil properties for tobacco cultivation which was mainly reflected in the following aspects: 1- The climate-related soil moisture regimes were generally used to classify the suborders in ST (2022). It was found that the soil moisture status of all pedons was Udic, as well as the fixed format of naming soils in ST (2022), Therefore, divisions were limited in the suborders, 2- The flexibility of WRB with the utilization of multiple qualifiers brings out more sensitivity in reflecting soil characteristics in the soil name if compared with Soil Taxonomy. Also, the emphasis put on soil morphology compared with laboratory data makes the system suitable for application in areas with rather modest facilities, 3- The existence of the Mollic or Umbric horizon in pedons is well defined by WRB (2022), while this issue is ambiguous in ST (2022), 4- WRB (2022) have not fixed naming formats, the number of secondary levels qualifiers of the WRB system could be increased or decreased with the number of diagnostic characteristics of the soil pedons. 5- Nomenculture is very complicated in both systems, nevertheless, it is inevitable to transfer information to non- specialist users in a more simpler language, in WRB (2022) this information can be extracted more easily from the soil name.

Keywords

• Udic
• Mollic
• Umbric
• Vertisols
• Soil Morphology
• North of Iran

Main Subjects

• Soil Genesis and Classification