Soil Genesis and Classification
Mahyar Moshtaghi; hasan ramezanpour; Nafiseh Yaghmaeian Mahabadi; Mahmoud Shabanpour
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 ...
Read More
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.
Soil Physics, Erosion and Conservation
Sahar Akhavan; Soheila Ebrahimi; Maryam Navabian; Mahmoud Shabanpour; Alireza Movahedi; Ali Mojtahedi
Abstract
Introduction Soil macropores are the prominent factor in the transfer of wastewater, fertilizers, and microorganisms, including fecal bacteria to deeper soils and even underground waters. On the other hand, a vast majority of land in Iran is located in arid and semi-arid regions. Therefore, the use of ...
Read More
Introduction Soil macropores are the prominent factor in the transfer of wastewater, fertilizers, and microorganisms, including fecal bacteria to deeper soils and even underground waters. On the other hand, a vast majority of land in Iran is located in arid and semi-arid regions. Therefore, the use of salty and unconventional waters has recently gained considerable importance. The aim of this study is to investigate the preferential transportation and storage of Escherichia coli (as an important bacterium in commonly used fertilizers) under the condition of saline water application. Materials and methods The laboratory studies were conducted in a preferential flow system with artificial macropores with different diameters (1 and 2 cm) and varying salinity treatments (1, 2 and 4 dsm-1) under a saturated flow condition. The leaching test was performed at 20°C within several phases. Microbial transfer tests were carried out in two phases with boundary conditions and flow velocities similar to the zero-phase condition. In order to evaluate the bacteria in the soil profile, after the end of the bacterial transfer test, the soil column was divided and cut into 3 layers. Two samples were collected from 3 depths and at macropore and matrix zones. The experiment was conducted in a factorial format and completely randomized design with three replications. The results showed that the mutual effect of salinity and macropore diameter was significant (at 5%) on mean output concentration (Cav), soil filtration coefficient (fλ), relative absorption index (SR), and maximal predicted depth of bacteria transfer (Zmax). Results The results indicated that the bacteria were affected by the treatments during the transfer, so that with increasing the salinity and reducing the diameter of macropores, the average bacterial concentration output decreased. The presence of macropores and the integrity of pores in a column with a diameter of 2 cm accelerated the bacterial movement and increased the pollutant outflow index due to high porosity; therefore, more bacteria passed (compared to the control column without macropores). The salinity treatment, however, served as an inhibitor and hindered further transmission of bacteria. Moreover, The macropore-free column with a salinity of 4 dsm-1 exhibited a higher refining coefficient (0.85 cfuml-1) compared to other treatments. A salinity treatment involving a 1 dsm-1 salinity and a pore diameter of 2 cm showed the least filtration coefficient (0.82 cfuml-1), so by doubling the ionic strength, 30% reduction can be seen in the bacterial filtration coefficient. Increasing the salinity up to 2 dsm-1 and decreasing the macropores diameter increased the relative absorption index. The macropore-free treatment with a 2 dsm-1 salinity showed the highest relative sorption index (0.92). Although the bacterial growth and mortality are unknown during the bacterial transfer process, according to the results, it is expected that the bacterial mortality rate increases by the salinity enhancement from 2 to 4 dsm-1 and the relative adsorption index reduction which may result in lower surface sorption. The significant treatment for the maximum predicted depth of bacterial transfer was the mutual effect of salinity and diameter at a probability level of 5%, which confirmed the significant impact of salinity on the bacterial filtration and transfer. The maximum depth of predicted bacterial transfer was obtained in the macropore-free treatment with the salinity of 1 dsm-1 (16.81 cm). The role of the underlying layers in the bacterial refinery seems to be more profound compared to the surface layer. Conclusion Overall, the results showed that the main source of transmission of bacteria is the preferential flow due to the macropore continuity. However, the salinity reduced the amount of bacterial refining by increasing the ionic strength of the soil solution. The salinity had a significant effect on the average output bacterial concentration, bacterial refining coefficient, relative sorption index, and maximum predicted bacterial transmission depth. The results of this study revealed that increased ionic strength of soil solution can enhance the bacterial refining and the further elimination of bacteria which can be effective in controlling the pollution of underground water by saline irrigation management. Regarding the quantitatively and qualitatively critical water status in the country, conditions can be provided for the use of unconventional water sources, without threatening the environment and contaminating the underground water.
