Soil science
Zeinab Barati; Hamidreza Owliaie; ebrahim adhami; Mahdi Najafi Ghiri
Abstract
Introduction
Zagros oak forest ecosystem is one of the largest forest ecosystems under destruction in Iran, which is of great importance in terms of water and soil protection. Moisture stress in recent years has caused the deterioration of these forests in a wide area. Iranian oak (Quercus brantii Lindlb.) ...
Read More
Introduction
Zagros oak forest ecosystem is one of the largest forest ecosystems under destruction in Iran, which is of great importance in terms of water and soil protection. Moisture stress in recent years has caused the deterioration of these forests in a wide area. Iranian oak (Quercus brantii Lindlb.) is the main tree species forming these forests. Potassium (K) is considered to be the most important nutrient cation in terms of its quantity in plant tissue and its physiological and biochemical functions. Soil tests measure the quantity of a nutrient element that is extracted from soil by a particular extracting solution. Over the years, many different soil testing methods and extracting solutions were evaluated to identify a technique that provides the most reliable prediction of crop yield response to nutrient application. It was determined that some soil testing procedures are best suited for particular soil types and climatic regions. There has been no research on the general status of K in the soil of Zagros forests, related to oak trees. It is important to introduce appropriate K extractants for extracting available K in these soils. Therefore, this research was carried out to achieve the mentioned goals in some forest areas of this Province.
Materials and Methods
Ten forest areas with dominant coverage of oak trees were selected in different parts of Kohgiluyeh and Boyerahmad Province. The physiochemical properties of the soil samples were determined based on standard methods. Soil pH, texture, electrical conductivity, calcium carbonate equivalent (CCE), organic carbon, and cation exchange capacity (CEC) were identified. The content of K present in different forms was determined by standard methods. Solution K was measured in the saturated extract. Exchangeable K was determined by extraction of 5 g soil sample with 20 mL 1 M NH4OAc (pH 7) for 5 min. Nitric acid-extractable K was measured by extraction of 2.5 g soil sample with 30 mL of boiling 1.0 M HNO3 for 1 h. Non-exchangeable K was calculated as the difference between HNO3-extractable K and NH4OAc-extracteable K. Total K was determined following digestion of 0.5 g soil sample with 10 mL of 48% HF and 1 mL of aqua regia. The 12 extracting solutions were 1M NaCl, 2M NaCl, 0.01M CaCl2, Morgan, AB-DTPA, 1M NH4OAC, 0.25M NH4OAC, 1M MgOAC, 1M NaOAC, 2M HCl, 0.1M HNO3, and 0.025M H2SO4. The K content of leaf samples was determined in 1g of each sample. The samples were dried and then ashed in 450°C for 4 h. 2M HCl was used to digest the samples. Potassium was measured on all filtrated extracts using a Corning 405 flame photometer.
Results and Discussion
The soils are all calcareous (average of 42.9 and 44.7% CCE in surface and subsurface, respectively), with pH in range of 7.0-7.8. The textural classes were sandy clay loam, clay loam, and clay. The range of soluble potassium is between 4.8 to 32.7 with an average of 15.4 mgkg-1, exchangeable potassium from 65.1 to 364 (with an average of 247 mgkg-1, non-exchangeable potassium from 106 to 876 with an average of 515 mgkg-1, structural potassium was from 761 to 7322 with an average of 4026 mgkg-1and total potassium was from 1051 to 8110 with an average of 4493 mgkg-1. Soluble, exchangeable, non-exchangeable, and structural potassium were 0.49, 9.6, 12.1, and 77.8%, of the total K, respectively. Among the 12 tested methods, 1.0 mol/L NH4OAC extracted the highest amount of K (mean 229.3 mgkg-1, ranging 64.9-384.2 mgkg-1) and 1.0 mol/L MgOAC removed the lowest amount of K (mean 53.0 mgkg-1, ranged 19.1-88.0 mgkg-1). Correlation coefficients between K extracted by 12 extractants were positive and significant. Maximum correlation between K leaf and extracted soil K was noticed in AB-DTPA, 0.25M NH4OAC, 1M NaCl, and Morgan-Wolfe (r=0.60, 0.59, 0.56, and 0.55, respectively) and the minimum correlation was noticed in 2M HCl and 0.025 M H2SO4 (r= 0.41 and 0.44, respectively). The amount of potassium in oak leaves (in the range of 0.65% to 1.18%) showed a significant correlation with exchangeable potassium in the soil. The amount of potassium in 50% of the oak leaf samples was less than the critical limit (1%). As a general result, 1M NaCl and 0.25M NH4OAC extractants are recommended for extracting potassium, due to greater correlation, simplicity of the method, and economic considerations.
Conclusion
The results of this research showed that the range of the values of different forms of potassium in different parts of the province had a relatively large difference (6 and 8 times difference in exchangeable and non-exchangeable potassium values). The amounts of available forms of potassium in the western regions of the province with less rainfall were in most cases higher than the more humid eastern regions. The average amount of exchangeable potassium in 60% of the studied areas was less than the critical limit of 250 mgkg-1 soil. Also, the average amount of leaf K in 50 percent of the samples was less than the critical level. Considering the great importance of potassium in the nutrition of oak trees and dealing with environmental stress, especially the shortage of soil moisture, it is recommended to pay more attention to the conditions of this element in the soil of the forest areas of the province. Also, fertilizing and foliar spraying of trees in some forest areas should be considered.
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 ...
Read More
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.
Soil science
H.R. Owliaie; E. Adhami; M. Najafi Ghiri
Abstract
IntroductionGlobal observations have confirmed that in recent decades, forests have been converted into agricultural land at a swift pace; this is a major global concern. Forests around the world have also experienced severe disturbances due to other anthropogenic activities. The conversion of forests ...
Read More
IntroductionGlobal observations have confirmed that in recent decades, forests have been converted into agricultural land at a swift pace; this is a major global concern. Forests around the world have also experienced severe disturbances due to other anthropogenic activities. The conversion of forests to cropland often results in soil degradation. Slope gradient and land use change are known to influence soil quality; therefore, the assessment of soil quality is important in determining sustainable land-use and soil-management practices. Magnetic susceptibility (χlf) measurements are widely used to study soil-forming processes. Many efforts have been made to correlate soil magnetic susceptibility with different soil properties, such as topography, parent material, Fe oxide forms, etc. The Yasouj area of Kohgilouye Province is one of the most densely forested areas in Zagros mountainous region. Parts of the area have been cultivated to feed the growing population, which has led to forest degradation. The objectives of this study were to assess some soil properties focusing on soil χlf and Fe- oxides forms in different land uses and slope positions.Materials and Methods Forty soil samples were taken from dense forest, sparse forest, eroded lands and dryland farming from different slops (0-15 and 15-30 percent) in Mokhtar Plain, west of Yasouj city. Soil samples were taken from the depth of 0–15 cm in a completely randomized design with five replications. Soil moisture and temperature regimes in the study area are xeric and thermic, respectively. Particle size distribution was determined by the hydrometer method and soil organic matter, CaCO3 equivalent and bulk density were determined using standard procedures. Fe (Feo) were extracted by acid ammonium oxalate, using a single 4-h extraction at pH 3 in the dark. Total free iron (Fed) was extracted with the CBD method. The total Fe contents (Fet) in the soil samples were determined after extraction with 5 mol L-1 HNO3. Magnetic susceptibility of the soils was measured at low (0.46 kHz; χlf) and high (4.6 kHz; χhf) frequencies, respectively; using a Bartington MS2 dual-frequency sensor, with approximately 10 g of air-dry soil in polyethylene vials. The percentage of frequency-dependent magnetic susceptibility (χfd%) was calculated to study the size of magnetic crystals in soils and the abundance of pedogenic ferrimagnetic in SP-SSD (~0.03 μm) boundary.Results and DiscussionThe results of this study showed that the land use and slope positions were among the important factors affecting the change of soil properties in this area. Land use change along with the reduction of organic matter reduced the stability of aggregates and increased land erosion. This process caused the loss of clay particles and magnetic minerals and affected many soil properties. Organic matter as an important indicator of soil quality, showed a decrease of about 3 times as a result of land use change from dense forest to eroded lands following by an increase in bulk density and a decrease in soil permeability and other soil quality indicators. Long-term afforestation and agricultural activities on sloping lands changed the soil texture from a class of silty loam in the forest to a lighter class of silty loam in agricultural use. Soil magnetic susceptibility, which is a function of soil magnetic particles was greatly affected by land use change and to a lesser extent by slope position. Due to the fact that magnetic susceptibility is influenced by factors such as soil texture, drainage class, erosion conditions, magnetic mineral contents, soil evolution conditions, land use changes from forest to other uses had significant effects (about 2 times) on χlf. Significant decrease in the amount of calcium carbonate in low slope positions was another reason for the increase in magnetic susceptibility in these positions. According to the measured values of χfd (ranged from 1.9 to 7.2%), the magnetic particles of the soils had low to moderate amounts of superparamagnetic (SP) particles, which indicates the combined effect of pedogenic superparamagnetic ultrafine particles and lithogenic (inherited) magnetic particles in χlf of the soils. The effect of slope on Fe forms (Feo, Fed and Fet) has been significant (p < 0.01) in almost all land uses. Due to the relatively high correlation of χlf with some soil properties such as Fe forms, soil clay, the amount of diamagnetic compounds including calcium carbonate in the studied soils, it is possible to estimate the value of these soil properties using χlf, which is a quick and cost-effective approach. Overall, it seems that magnetic susceptibility could be applied successfully to estimate some soil properties in hilly regions of Zagros Mountains of southwestern Iran, especially for monitoring the consequences of land use changes. It should also be noted that any change in the use of the area should be defined in accordance with the potential of the land in the long term to prevent a reduction in soil quality.
