Soil science
H.R. Owliaie
Abstract
Introduction
Soil classification is the systematic categorization of soils based on distinguishing soil characteristics, aiding in the comprehension of soil properties through soil surveys, and establishing suitable strategies for effective soil utilization and management. One of the main reasons ...
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Introduction
Soil classification is the systematic categorization of soils based on distinguishing soil characteristics, aiding in the comprehension of soil properties through soil surveys, and establishing suitable strategies for effective soil utilization and management. One of the main reasons for creating soil classification systems is to identify the differences in important soil characteristics for management purposes. Globally, Soil Taxonomy (ST) and the World Reference Base for soil resources (WRB) are widely used for soil classification. However, these two classification systems have varying criteria which can pose difficulties when exchanging classification results. After years of intensive worldwide testing and data collection, new versions of the ST and WRB systems have been released. In its current state, ST has a strong hierarchy with six categorical levels: order, suborder, great group, subgroup, family, and series (Soil Survey Staff, 2022), while the WRB has a flat hierarchy with only two categorical levels: reference soil groups and soil units (IUSS Working Group WRB, 2022). Several scientists have endeavored to evaluate the merits and demerits of these soil classification systems and offer recommendations for their enhancement. The arid and semi-arid regions located in the western and southwestern parts of Kohgiluyeh and Boyerahmad Province, distinguished by their considerable diversity in parent materials, topography, climate, and land use, present an excellent opportunity for scrutinizing and contrasting the effectiveness of soil classification systems. Remarkably, no prior research has delved into this subject in this specific geographical area. Consequently, this research aims to compare the effectiveness of the ST and WRB systems in characterizing soil attributes. Furthermore, it seeks to analyze the alterations that these two systems have undergone during an eight-year period, spanning from 2014 to 2022.
Materials and Methods
This study was conducted in the western and southwestern regions of Kohgiluyeh and Boyerahmad Province, specifically in the divisions of Gachsaran, Basht, Choram and Kohgiluyeh. A total of 26 soil profiles were excavated, described, and sampled based on aerial photos, satellite images, topographical and geological maps, as well as field observations. These profiles were selected following the soil description guide provided by the Department of Soil Conservation of the US Department of Agriculture. Subsequently, after reviewing the preliminary results and aligning with the research objectives, 12 representative soil profiles were chosen for further analysis. Soil samples were collected from all genetic horizons and transferred to the laboratory. After air-drying, the samples were passed through a two-millimeter sieve and the routine physical and chemical analyses were conducted, including soil texture, pH, electrical conductivity (EC), calcium carbonate equivalent (CCE), organic carbon, cation exchange capacity (CEC), and gypsum analyses. For mineralogical studies, soil clay minerals were separated and identified using standard methods. Additionally, soil thin sections were prepared from intact soil samples of selected soil horizons and examined under a polarizing microscope. Finally, the soil profiles were classified based on the criteria outlined in Soil Taxonomy (2022) and WRB (2022).
Results and Discussion
Soil Taxonomy and WRB, as the two most popular classification systems, aim to encompass as manysoil characteristics as possible. According to the ST classification, the soils were classified into four orders: Entisols, Inceptisols, Alfisols, and Mollisols. In the WRB system, they were grouped into seven reference soil groups: Regosols, Flovisols, Luvisols, Cambisols, Kastanosems, Gypsysols and Glysols. The results revealed that WRB was significantly more effective in describing the characteristics of the studied soils. One of the key advantages of this two-level system is its flexibility, allowing for the inclusion of additional principal and supplementary qualifiers to cover all essential soil characteristics. Moreover, in many cases, WRB exhibits better prioritization compared to ST. For example, the presence of gypsic, combic, calcic horizons, as well as fluvic and gley properties, can allocate the soil to the reference groups of Gypsisols, Cambisols, Calsisols, Fluvisols, and Gleysols, respectively. However, a limitation of the WRB system is the absence of mineralogical information in soil classification. Enhancing this classification system's quality and making it more appealing to planners could be achieved by incorporating suitable mineralogical attributes for the reference groups or criteria that express soil fertility conditions with relatively straightforward measurements. In addition, it is proposed to add three subgroups to ST: Gypsic Haplustalfs, Fluventic Gypsiustepts and Cambic Haplustolls. Similarly, following the WRB model, it is recommended to introduce a qualifier in ST to indicate the presence of lithological discontinuity. Regarding the WRB system, suggestions include adding qualifiers such as "Cutanic" to gypsisols with clay films, "hypercalcic" to reference groups of Kastanozems and Luvisols with a calcic horizon comprising more than 50% of calcium carbonate, and "aridic" for better expression of soil characteristics with Aridic-Ustic moisture regimes.
Conclusion
The results of this research demonstrated that WRB is more effective in describing the conditions and characteristics of the studied soils. The WRB system, through its diverse set of qualifiers, is capable of representing field conditions more efficiently. However, it is suggested that the surveyors have the freedom to select an appropriate qualifier from the list provided by WRB without limitation, which can enhance its success in practical applications. Furthermore, it is recommended that both classification systems be used to categorize soils, not only to evaluate their efficiency for the soils in other regions but also to gain a comprehensive understanding of their suitability for different contexts.
Z. Saieedifar; H.; F. Akram ghaderi
Abstract
Introduction: Soil compaction has become a widespread problem in the world and it is considered as one of the main factors affecting land degradation in arid and semi-arid agricultural land. Compaction in arable soils is a gradual phenomenon that appearing over time and most important factors that influence ...
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Introduction: Soil compaction has become a widespread problem in the world and it is considered as one of the main factors affecting land degradation in arid and semi-arid agricultural land. Compaction in arable soils is a gradual phenomenon that appearing over time and most important factors that influence it include: soil properties, high clay content, low organic matter, and frequency of wet-dry in the soil, impervious layer of soil, load heavy agricultural implements and soil and water mismanagement. Compaction induced soil degradation affects about 68 million hectares of land globally. The vast majority of compaction in modern agriculture is caused by vehicular traffic. Carbon sequestration by long-term management operation of the plant and soil, not only increase the soil carbon storage but also lead to reduce the carbon exchange and greenhouse gases emissions like CO2 from the soil profile. The aim of this study was evaluating the effect of soil compaction on carbon and nitrogen sequestration of wheat and soil and some soil physical properties such as: aggregate stability, saturated soil moisture content, bulk density and soil porosity.
Materials and Methods: This experiment was accomplished in which is located near Aq Qala in a randomized completely block design (with 4 treatments and 3 replications). Soil compaction was artificially created by using a 5/7 ton heavy tractor. The treatments arrangements were: 1) T1: control, 2) T2: twice passing of tractor, 3) T3: four time of passing tractor, and 4) T4: six time of passing heavy tractor. Utilize of all agricultural inputs (fertilizers, herbicides, etc.) has been identical for all treatments. Since rain-fed farming is the common method to cultivation of cereals in the study area, so no complementary irrigation was carried out in this period. In this study, after the measurement of the parameters, the data were analyzed by using SPSS 16.0 Software. LSD test was used for comparison of means.
Results and Discussion: The results showed that the different levels of soil compaction significantly increased soil bulk density. All the soil compaction treatments have caused a significant reduction on carbon and nitrogen sequestration in soil and wheat, soil aggregates stability and saturated soil moisture values. In the other hand the amount of soil pH and EC has increased significantly by increasing soil compaction levels that Indicates the negative effect of compaction on salinization of arable land.
Conclusion: The results of this study showed that the negative effects of soil compaction on soil physiochemical attributes are dependent on escalation of compaction. In total, even low levels of soil compaction (the treatment of two passes of a heavy tractor) is able to remarkably alter soil physiochemical attributes and thus carbon and nitrogen sequestration in soil and wheat. Induced changes in nitrogen and carbon sequestration levels are important for who concerned of global warming and climate change. Regarding the inability of deactivating soil compaction adverse effects in the deep soil layers of agricultural fields is the best way of handling and preventing soil compaction. Using these sluggish renewable resources should be consistence with land capability and its physical nature. This type of land use will result in sustainable development. From the remarks given here, it might be concluded that revising agricultural regimes and production methods is inevitable. On this ground, revisiting current agricultural systems should be considered and an urgent demand for state-of-the-art methods consistent with environmental objectives is being felt. To prevent soil compaction as much as possible, tractors and machinery traffic must be avoided to an acceptable level and this is of high priority during the time which soil is wet. It is more preferable to perform the operations with lighter machineries. As much as possible in a sophisticated agricultural plan these recommendations must be considered:
Increasing soil organic matter, leaving crop residue from the previous crop at the soil surface, using crops with deep-and-vertical-penetrating roots during crop rotation, tillage depth variation in different years, using super absorbent for better ventilation and reduces soil compaction, implementing no-tillage system to reduce traffic of farming machineries, maintaining plant residues at the soil surface, applying lacking nutrients to the soil, and subsoil operations to reduce the detrimental effects. As a field-based study, the results could be transferred to the local farmers. Authorities have to remove the obstacles to deliver the message to the farmers in order to enhance production and reach nation self-sufficiency.
