Research Article
M. Kaveh; M.A. Esmaili; Hematolah Pirdashti; M.R. Ardakani
Abstract
Introduction: Rice is a staple food source and the most important grain in developing countries, which is most commonly consumed by more than 90 percent of the world populations. Moreover, this plant is produced and consumed in Asia. However this major crop faces severe limitations such as water scarcity ...
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Introduction: Rice is a staple food source and the most important grain in developing countries, which is most commonly consumed by more than 90 percent of the world populations. Moreover, this plant is produced and consumed in Asia. However this major crop faces severe limitations such as water scarcity and other environmental stresses. Limited water resources along with climate change effects, have increased attention to methods which improve water use efficiency in crops such as rice cultivation. On the other hand, traditional irrigation methods for rice production often waste considerable fraction of irrigation water. Therefore, it is necessary to modify irrigation and other farming methods. Furthermore, using biochar and nitrogen fixing bacteria as organic biofertilizers can be effective methods to improve water use efficiency and yield attributes of rice plant. Therefore, the present research was conducted to investigate the effect of biochar and Azosprillum lipoferum rhizobacteria on yield and water use efficiency on Tarom Hashemi rice cultivar of under flooded and alternating irrigation regimes. Materials and Methods: This study was conducted at the research fields of the Sari Agricultural Sciences and Natural Resources University in 2017 and 2018. The experimental site is located at 36º 39ʹ42ʺ N latitude and 53º03´54ʺ E longitude with -11 m above sea level. Soil samples were taken from depths of 0-30 cm before land preparation. The experiment was done in factorial split-split plot arrangement with complete randomized blocks based design with three replications. Treatments included two irrigation management methods (flooding and irrigation regimes) in combination with nine fertilizers levels (100% of recommended nitrogen or N100, N100+ 10 ton biochar or biochar 10, N100+ biochar 20, N75, N75+ biochar 10, N100+ biochar 20, N50, n50+ biochar 10 and N100+ biochar 20) as main plots and seedling inoculation with Azospirillum lipoferum bacteria (without inoculation was also included as control) as sub plots.Plot ridges were covered by plastic sheets and inserted into the soil at 50 cm to prevent water flowing from one plot to the others. The plots were then leveled and 3-4 leaf seedlings stage. A specific number of seedlings were gently washed and placed for 30 minutes in a pan containing 10 L of water mixed with 1 L of bacterial inoculum. Carboxymethyl cellulose, 15 g, was added to increase adhesion of bacteria into the plant roots. Nitrogen, phosphorus and potassium fertilizers were applied according to the results of soil analysis. Weeds and pests were controlled mechanically or by hand and no herbicides or pesticides were used. Results and Discussion: Results showed that biochar and nitrogen fertilizers, irrigation methods, and seedling inoculation with bacteria had significant effects on water use efficiency indices. Comparison of means of interaction effects showed that the highest paddy yield (5950.43 and 5330.78 kg/ha, respectively) were observed by flooding irrigation method in combination with N50 + biochar 20 treatment and inoculated by Azospirillum lipoferum bacteria and alternating irrigation management method which was along with N50 + biochar 20 without inoculation. Alternating irrigation plots experienced water shortage in some growth stages and therefore slightly lower paddy yield is acceptable. Application of biochar 20 and flooding or alternating methods which treated by N75 and N50, respectively showed 49.1% increase in economic efficiency index. Conclusion: In general, application of 20 ton biachar along with 75% nitrogen fertilizers led to 42.8% increase in economic advantages in alternating irrigation method as compared to the flooding systems. These observation indicates beneficial effect of fertilizer in economic advantage enhancement in rice cultivation.
Research Article
M. Karimi Fard; M. Zakerinia; A.R. Kiani; Mohammadtaghi Feyzbakhsh
Abstract
Introduction: Rice is the second most important edible grain after wheat in Iran. The most important factor for sustainable production in rice production lands, is water. Almost 75 percent of the world's rice is produced from paddy fields and rice is the largest consumer of water among all crops. Its ...
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Introduction: Rice is the second most important edible grain after wheat in Iran. The most important factor for sustainable production in rice production lands, is water. Almost 75 percent of the world's rice is produced from paddy fields and rice is the largest consumer of water among all crops. Its growth is significantly affected by climate change and water scarcity. This research was carried out to compare the direct cultivation and transplanting of rice under different irrigation methods from the point of view of water productivity. Material and Methods: The current work was designed as split plot based on randomized complete block design with 6 treatments and three replications in 18 plots with 6 m wide and 12 m length (72 m 2) in area of approximately 1500 m2 at the Agricultural Research Station of Golestan province in spring and the summer of 2018. Treatments including three levels of basin irrigation, sprinkler and drip (tape) irrigation were considered as main factors and two methods of direct cultivation and transplanting were considered as sub-factors. Results and Discussion: The results of analysis of variance showed that the effect of irrigation and sowing method on the yield of rice were significant at 0.01 level probability. The highest amount of biological yield in transplanting was obtained by basin irrigation (8177 kg/ha) and in direct seeding in basin irrigation and taper irrigation (7375 and 6836 kg/ha, respectively). The highest 1000-grain weight in transplanting method was obtained in basin irrigation and direct seeding method in traditional irrigation and tape irrigation. The highest number of filled grains in the panicle was observed in the basin irrigation treatment in transplanting, with significant difference compared to the amount observed in direct seeding. Traditional irrigation between planting methods had not significant effect on the number of hollow grains; while in sprinkler and tape irrigation (with an average of 51 and 56 for sprinkler and tape irrigation, respectively), the number of hollow grains had a higher rate in direct seeding (with an average of 41 and 45 for sprinkler and tape irrigation). The results showed that basin irrigation with 8177 kg/ha grain yield in transplanting method and basin and tape irrigations with 7375 and 6836 kg/ha in direct seeding method had the highest grain yield. Sprinkler irrigation had the lowest paddy yields in transplanting (4188 kg/ha) and direct seeding (5712 kg/ha). Tape irrigation with 7390 and 6840 m3 of consumed water, resulted in lower water consumption compared to traditional irrigation (10700 and 1693 m3), respectively. The highest amount of water use efficiency was obtained in direct and tape irrigation (0.99 kg/m3) and in traditional and tape irrigation (0.76 and 0.66 kg/m3, respectively). Conclusion: Adjusting water consumption both through lower water consumption and reduced water wastage can lead higher water productivity of rice production systems creating sustainable rice production systems. In transplanting method, tape irrigation and traditional irrigation had higher water use efficiency than sprinkler irrigation, although a significant water use reduction in tape irrigation rather than basin irrigation should be analyzed economically at real water prices. Overall, in this study, the tape irrigation method, by reducing water consumption, was able to increase water productivity and maintain the yield of rice in direct cultivation. Sprinkler irrigation had the lowest yield of rice in transplanting and direct cultivation. Problems such as lack of uniformity of spraying and waste water through the wind as well as poor quality of sprinklers are the main reasons for the decrease of the efficiency of sprinkler irrigation.
Research Article
M.R. Ansari; F. Soleimani; A. Ahmadi
Abstract
Introduction: Soil erosion is the most widespread form of soil degradation jeopardizing food security worldwide. In Iran, gully erosion is important because about 90% of the country has arid and semi-arid climates and rainfall is not adequately distributed. In such conditions, the absence or lack of ...
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Introduction: Soil erosion is the most widespread form of soil degradation jeopardizing food security worldwide. In Iran, gully erosion is important because about 90% of the country has arid and semi-arid climates and rainfall is not adequately distributed. In such conditions, the absence or lack of vegetation cover with increasing runoff causes more than 2 billion tons of soil losses annually. Therefore, conducting basic and applied researches on soil erosion via different methods for comprehensive management of natural resources is emphasized. The prerequisite for all kinds of erosion, such as gully erosion, is the prediction of the risk of gully formation in different areas susceptible to erosion. Materials and Methods: The study area is located in Ghaleh Gorg watershed which sub-basin of Shahid Modarres that large part of these farmlands has been destroyed by gully erosion. The purpose of this study was to apply fuzzy logic operators for gully erosion zoning. In this research, six effective parameters on soil erosion including mean weight diameter of aggregate, sodium adsorption ratio, salinity, percent of fine sand, silt and clay were determined according to standard laboratory methods. After re-classification, standardization of prepared layers was carried out by the Fuzzy method. Hence, Fuzzy-based layers were integrated using operators of Fuzzy algebraic sum, Fuzzy algebraic production and Fuzzy gamma with 0.2, 0.5, 0.8, 0.9 values and the obtained results were evaluated. The validation of prepared maps was done based on two methods of map matching percentage of areas with very high and high sensitivity with gullies map of the study area and quality sum index (Qs). Results and Discussion: The Fuzzy results of raster layers showed the relative accumulation of silt, clay and fine sand grains in the middle to western parts of the region due to leaching and soil aggregation of Aghajari formation with a high slope of >20%. The deposition of this sediments was with 0-5% slope in the middle and western part of the basin. Results of layer integration indicated the fact that the fuzzy summation and multiplication method are not suitable approaches for final mapping because of their high increasing and decreasing effects, respectively. About Fuzzy Gamma operator 0.2, the results revealed that about 17.07% of the area was in the high and very high-risk zone and 67.07% of the area was in the low risk zone. In Fuzzy Gamma 0.5, about 31.16% of the area was in high risk and 55.38% in low risk zone. And only 60.38 percent of the gullies was in the high-risk area. Thus, these both operators 0.2 and 0.5 cannot be an acceptable method for preparing the final fuzzy map. The results of gamma operator 0.8 showed that about 43.21% of the area was in high and very high risk classes and 42.45% of the area was in low and very low risk classes. In the gamma operator 0.9, about 60.92% of the area was in high and very high risk zone and 17.1% of the area was in low and very low-risk zone. Also, regarding the distribution range of gullies, 94.93% of gullies was in high and very high risk classes, which is more acceptable and better than gamma 0.8. According to the obtained results, Fuzzy gamma 0.9 with 94.93 matching percentage of areas containing very high and high sensitivity and maximum quality sum index (0.73) among different operators was selected as the best method for preparing Fuzzy map in the study area. Conclusion: According to the results of this study and its comparison with field observations, effective factors contributing to the initiation and development of gully erosion were sensitivity of the geological formations, soil texture type, salinity and alkalinity and non-implementation of biological and biomechanical operations to the soil and vegetation cover restoration. Around 3855 hectares (60.38%) out of 6327.5 hectares of the total studied area were at high and very high erosion risk. Furthermore, 2056 hectares (94.93%) out of the 2166 hectares of the gullies area were at high and very high risk of erosion, denoting the high accuracy of the final map. Among the available methods, Fuzzy Gamma 0.9 with the highest overlap between the area of high and very high-risk classes of the gully map (94.93%), and the highest qualitative sum index (0.73), was selected as the best fuzzy method for zoning in the study area.
Research Article
E. Shirmohammadi; H.A. Alikhani; Ahmad Ali Pourbabaee; H. Etesami
Abstract
Introduction: Stresses of drought, salinity and deficiency of nutrients especially phosphorus (P) are the most important challenges for wheat production in Iran. One of the ways to achieve more wheat yield production is increasing of this plants tolerance to stresses of water-deficit, salinity and deficiency ...
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Introduction: Stresses of drought, salinity and deficiency of nutrients especially phosphorus (P) are the most important challenges for wheat production in Iran. One of the ways to achieve more wheat yield production is increasing of this plants tolerance to stresses of water-deficit, salinity and deficiency of essential elements such as P; and/or alleviate destructive effects of these stresses. In this respect, use of PGPR can be useful. Research has shown that PGPR with multiple mechanisms reduces the negative effects of water-deficit and salinity stresses, and also increases the resistance of plants to these stresses, which ultimately leads to increase of plants growth. This study was designed and carried out to investigate the effect of three superior PGPR on qualitative and quantitative indices of wheat under water-deficit stress in saline soil. Materials and Methods: The soil used in this experiment was collected from longitude of 49° 26' 25'' E, latitude of 35° 52' 26'' N and elevation of 1534 m (located in the Qazvin province of Iran) from depth of 0-30 cm of soil. According to the experimental design, 3.5 kg of soil with applying P-fertilizers treatments was filled to the pots. The factorial arrangement based on completely randomized design (CRD) was used in this study. The treatments were replicated three times. The first factor: soil water content at two levels including 80% and 55% FC (W80 and W55); the second factor: Bacterial inoculants at four levels including control or non-inoculated seeds with bacterium (B0), inoculated seeds with Bacillus pumilus strain W72 (B1), inoculated seeds with B. safensis strain W73 (B2), inoculated seeds with Staphylococcus succinus strain R12N2 (B3); and the third factor: P-fertilizers at six levels including control or non-treated plants with P-fertilizers (F0), and plants treated with (rock phosphate) RP - (F1), RP + 19 mg triple superphosphate (TSP) / kg of soil (F2), RP + 38 mg TSP / kg of soil (F3), RP + 57 mg TSP / kg of soil (F4), with 57 mg TSP / kg of soil (F5), generally there were 144 experimental units (pots). Also, 192 mg RP (containing 13.8% P2O5 or 6.13% P) was mixed per kg of soil in each of RP treatments. Statistical analysis of data was performed using SAS software and comparison of means was evaluated by using the Tukey's test (HSD) at p < 0.05 level. There were 5 plants in each pot and irrigated up to 80% FC with distilled water. With the beginning of stem elongation stage, water-deficit stress was applied and continued until the harvest. During the experiment, pots were kept in greenhouse at 25/20±2°C day/night temperatures and 16 h photoperiod with 23,000 lux light intensity. At the end of the experiment, plants height, fertile clusters, root dry weight /shoot dry weight ratio, total dry weight of plant, grain number, thousand grain weight, also, root, shoot and grain P-concentration were measured. Results and Discussion: Generally, it can be said that the moisture level of W80 compared to W55 increased all of measured traits in wheat plant. Due to the unique properties of water and its role in biological and non-biological reactions, by reducing soil water content to near of the permanent wilting point (W55), water absorption by the plant hardly occurs. Therefore, the plant needs to consume more energy for water absorption or grow with less water than normal status, which these factors disturb the metabolism of cells and eventually decreases natural activity and growth of plant. Also, it seems that under water stress condition, wheat plant by formation of “Rhizosheaths” around of their own roots, enters to the defensive phase and by this strategy prevents expansion of their own rhizosphere. With attention to the special importance of the rhizosphere in the supply of water, nutrients and activity of microorganisms, as well as the effect of microorganisms secretion and root exudates on the solubility and availability of nutrients. Thus, it is reasonable that qualitative and quantitative traits of plants decrease by reduction of the rhizosphere diameter due to the water-deficit stress. There was no significant difference between application of rock phosphate and control (F0) for most of measured traits of soil and plant; but, application of RP with bacterial treatments (B1 and B2 at W80 and B3 at both level of W55 and W80) compared to the control, often increased measured traits. Also, each level of TSP compared to the control, often increased this trait. Research indicates that RP can be used as a P-fertilizer, but its efficiency depends on its reactivity in the soil. There is ample evidence that RP has not enough efficiency in neutral and alkaline soils; but, it can be used as the P-fertilizer with proper efficiency in acidic soils or alkaline soil with application of PGPR. Often, all of three bacterial treatments (B1, B2 and B3) at level of W80 and B3 treatment at level of W55, compared to control (without bacterial inoculation) improved qualitative and quantitative traits of plant. Research also shows that under stressful and non-stressful conditions, PGPR can improve plant growth by different strategies. However, this microorganism does not always improve plant growth under all conditions. It seems to be due to differences in genetic and function of bacteria and with conditions change, each bacterium may behave differently. Conclusions In general, for wheat cultivation that may get exposed to moisture stress at one or more stages of its growth (such as dry-farming of wheat), the use of B3 bacterial inoculant (Staphylococcus succinus strain R12N2) seems appropriate for crop management. Because in this study at both W80 (non-water-deficit stress) and W55 (severe water-deficit stress) levels of soil water content, B3 treatment increased qualitative and quantitative of wheat traits. In other words, because of the natural conditions of the dryland farming, the probability of precipitation is different; it seems that B3 treatment can increase wheat production under these conditions. However, the use of this bacterium as a biofertilizer for dryland wheat farming in Iran or other place of the world requires further testing and evaluation in dryland farms of that countries.
Research Article
atena mirbolook; Mirhasan Rasouli-Sadaghiani; E. Sepehr; A. Lakzian; M. Hakimi
Abstract
Introduction: Iron (Fe) is an important micronutrient that plays a role in several crop physiological processes such as photosynthesis, respiration, and synthesis of heme proteins, DNA, RNA, and hormones. The most common Fe source used in agriculture is Fe-EDDHA. However, the usage of this chelate may ...
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Introduction: Iron (Fe) is an important micronutrient that plays a role in several crop physiological processes such as photosynthesis, respiration, and synthesis of heme proteins, DNA, RNA, and hormones. The most common Fe source used in agriculture is Fe-EDDHA. However, the usage of this chelate may be problematic for plant growth. In the recent years, organic chelates have gained attention as they increase the microelements solubility and prevent iron precipitation in nutrient solution. Organic chelates such as amino acids and polysaccharides have many physicochemical (reactive OH, COOH and NH2 groups) and biological (biocompatible and biodegradable) properties that make these attractive materials usable for the agricultural practice. Biodegradability, low toxicity, immune system stimulation, the ability to coordinate metal, less sensitivity to photodegradation, and the effect on physical properties of rhizosphere and root growth dynamic are ideal properties of these components. The objective of this study was to evaluate Fe-organic-chelates efficiency as Fe sources for bean (Strategy I) and corn (Strategy II) growth in the hydroponic system. Materials and Methods: In this research, we synthesized Fe-amino acid chelates including Fe-Glycine (Fe-Gly), Fe-Phenylalanine (Fe-Phe), Fe-Tyrosine (Fe-Tyr), Fe-Methionine (Fe-Met), and Fe chitosan chelates in two forms of acidic hydrolyzed chitosan [Fe-C(A.hyd)] and enzymatic hydrolyzed chitosan [Fe-C(E.hyd)] and characterized by FTIR and CHN analyzer. The efficiency of these iron sources for bean (Strategy II) and corn (Strategy I) in hydroponic system was then evaluated. Seeds of bean and corn were washed with distilled water and transplanted into special containers containing coco peat, perlite and vermicompost (1:1:1) at 25 °C for germination and initial growth. The seedlings were transferred to polyethylene plastic lids fitting tightly over 8-L polyethylene containers under controlled conditions in the greenhouse with a light period of 8 hours per day, the temperature of 20 to 25°C and relative humidity of 65 to 75%. The pots were stacked in black color to prevent light reaching the root of the plant and the solution. In each pot, one plant seedling was placed and the basic nutrient solution was prepared in deionized water. The plants were harvested after 8 weeks, their root and shoot were separated and dried after washing with distilled water in an oven at 75 ° C. The dried samples were ground to fine powder to pass through a 20-mesh sieve. The analysis of Fe in samples was performed using atomic absorption spectrophotometer. Result and Discussion: Application of organic chelates of amino acids and chitosan increased the shoot dry matter per plant compared to Fe-EDDHA. Fe content in shoot of corn and bean was highest using Fe-Tyr, Fe-Met and [Fe-C(A.hyd)]. Uptake and accumulation of Fe in roots were observed by using all chelates, but the highest translocation factor was found for the treatments including [Fe-C(A.hyd)] and Fe-Tyr. Translocation factor in bean plants was higher than corn, and around half of Fe in bean plants was translocated from root to shoot. The use of iron chelates in plant growth medium increased the activity of ferric chelates reductase enzymes in bean and corn compared to Fe-EDDHA. However, the mean of this enzyme activity in bean was higher than that in corn. Therefore, the activity of this enzyme can be used as an indicator for determining the iron availability in leaf cells in Strategy I and Strategy II plants. In general, the plants need less energy to absorb Fe when the chelates with a simpler structure are used. Conclusion: The results indicated that using Fe organic chelates in the hydroponic system could supply sufficient amounts of iron for the plant uptake and also improve the root and the shoot growth of bean and corn. Overall, the effect of Fe organic chelates on Fe content of bean and corn shoots was in the following order: Fe- Chi(A.hyd) > Fe-Tyr > Fe-Met > Fe-Gly >. Activity of leaf ferric chelate reductase in bean was higher than that in corn.
Research Article
S. Sanjari; M.H. Farpoor; M. Mahmoodabadi; S. Barkhori
Abstract
Introduction Increasing demand for an international classification system as a unique communication tool in soil science has caused development of different systems. Like many other countries, Soil Taxonomy and WRB are the most popular soil classification systems in Iran. Genetic and morphologic ...
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Introduction Increasing demand for an international classification system as a unique communication tool in soil science has caused development of different systems. Like many other countries, Soil Taxonomy and WRB are the most popular soil classification systems in Iran. Genetic and morphologic soil properties are used for soil classification in both systems. However, correlation of the two systems and efforts to harmonize them have been a major concern among soil scientists. Comparing Soil Taxonomy and WRB in gypsiferous and calcareous soils of central Iran, Sarmast et al. (13) reported that WRB using various qualifiers is more effective than Soil Taxonomy. Since no study on soils of Iranshahr and Dalghan Regions located in Sistan and Baloochestan Province has performed and/or no reported data is available, the present research was performed to: 1) study morphological, physical, and chemical soil properties in the area, 2) classify soils based on Soil Taxonomy (2014) and WRB (2015) systems, 3) compare the two systems for soil description in Iranshahr and Dalghan regions as a part of Sistan and Baloochestan Province, central Iran. Material and Methods: The study area starts from Iranshahr (590 m asl) in the center of the province and extends to Dalghan (390 m asl) in west. Alluvial fan, pediment, playa, and hill were among different landforms identified using field studies, topography maps (1:50000), and Google Earth image observations. To cover the maximum soil variations in the area, 10 representative pedons were selected, described, and sampled. Results and Discussions: Calcic, gypsic, anhydritic, argillic, natric, and salic horizons identified after field work and laboratory analysis. Results of the study showed that addition of Yermic Torrifluvent, Yermic Torriorthent, Calcic Gypsiargid, Gypsic Natrsalid, Natric Gypsisalid, Anhydritic Gypsisalid, Anhydritic Calcisalid subgroups to Soil Taxonomy system from one hand, and addition of anhydrite and aquic (for Solonchak reference soil group) qualifiers to WRB system from the other hand, causes a higher correlation and more harmonization between the two classification systems. Meanwhile, the minimum percentage of calcium carbonate equivalent necessary for calcic horizon identification in coarse textured soils including gravel in Soil Taxonomy is also suggested to be added to WRB system. Besides, requirements of salic horizon in WRB system is recommended to be added to Soil Taxonomy. At the same time, soil names in WRB system provide more information and data about soil properties and characteristics in young soils (such as yermic qualifier showing desert pavement) compared to Soil Taxonomy. Soil Taxonomy is not able to properly classify saline soils of arid regions down to subgroup level which is a weak point for this system. That is why newly added Gypsic Natrsalids is suggested for soils with natric, gypsic, and salic horizons in the upper 100 cm of the soil. On the other hand, the requirements of salic horizon in WRB system (the minimum EC content of 15 dS/m and the EC multiplied by the horizon thickness of more and/or equal to 450) are also suggested for Soil Taxonomy. Conclusion: Results of the study for both saline and sodic soils show more capability of WRB system compared to Soil Taxonomy to classify soils. From soil management point of view, natric horizon causes more negative effects compared to salic horizon because Na disperses the soil particles and destroys soil structure and sodic soils need more practices to be improved compared to saline soils. Results for gypsiferous soils also show more capability of WRB system compared to Soil Taxonomy because gypsum content which is important for gypsiferous soils management is properly concerned in WRB system. However, lack of anhydritic horizon in WRB seems to be a weak point for this classification system. That is why it is suggested to be added to WRB (13). Since Soil Taxonomy does not use independent abbreviations for anhydritic horizon compared to gypsic horizon, the Ba and Baa abbreviations are also suggested for Soil Taxonomy to be added.
Research Article
Sh. Haghighi; Z. Sharifi
Abstract
Introduction: Calcareous soils are described as soils containing quantities of calcium carbonate which have an enormously effect on the soil properties (physical, consisting of soil water relations and soil crusting, or chemical consisting of the availability of plant nutrients) and plant growth. Calcareous ...
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Introduction: Calcareous soils are described as soils containing quantities of calcium carbonate which have an enormously effect on the soil properties (physical, consisting of soil water relations and soil crusting, or chemical consisting of the availability of plant nutrients) and plant growth. Calcareous soils arise clearly in arid and semi-arid areas due to rare precipitation and little leaching. It has been evaluated that these soils contain over one-third of the world's surface zone and their CaCO3 content ranged from a few to 95%. Calcareous soils faced many challenges such as shortage of organic matter, low structure stability, low water holding capacity, low CEC, high pH, surface crusting and cracking and great infiltration rate which cause loss of essential plant nutrients via leaching or deep percolation. Another problem in calcareous soils is low availability of plant nutrients particularly phosphorous and micronutrients specially zinc, iron and manganese, and a nutritional imbalance between elements such as potassium, magnesium and calcium. Although a calcareous soil is dominated by free lime, it could also incorporate large quantities of iron, aluminum, and manganese. These metals provide more strong sorption sites for phosphorus and are mostly more significant in controlling phosphorus solubility in calcareous soils than calcium carbonate itself. Under such severe conditions, desired yield levels are difficult to attain. Calcareous soils lack the organic matter required for optimal crop yield. Therefore, numerous studies have made efforts to increase the availability of nutrients in the soils through different treatments. Common methods for dealing with these deficiencies, is the use of chemical fertilizers that have the risk of environmental pollution in addition to the high cost and low efficiency. Oxidation of sulfur leads to sulfuric acid formation which can decrease the soil pH and increase dissolution of insoluble soil minerals and release of essential plant nutrients. Furthermore, the addition of organic amendments improves the soil chemical and physical properties, initiates nutrient cycling, and provides a functioning environment for vegetation. Materials and Methods: The objective of this research was to increase solubility of nutrient elements in a calcareous soil considering nine treatments (i.e., control (Blank), Soil + Humic Acid (HA), Soil + Sulfuric Acid (H2SO4 ), Soil + Thiobacillus (T), Soil + Sulphur (Sº), Soil + Sulphur + Thiobacillus (Sº +T), Soil + Vermicompost (VC), Soil + Vermicompost + Thiobacillus (VC+T) and Soil + Sulphur + Vermicompost + Thiobacillus (Sº +VC+T)). The experimental design was factorial arrangement in randomized complete block, with all the treatments replicated three times. All the treatments were incubated under the laboratory condition for 90 days in 25 ± 2 °C and 70% of water holding capacity by distilled water. During the incubation period, the moisture of the samples was kept at 70% FC by daily addition of deionized water based on weight loss. At the end of incubation period the pH value, electrical conductivity (EC), available form of macro elements (K, P and N) and micro elements (Zn, Mn, Fe and Cu) were determined in all treatments by standard methods. Results and Discussion: The results showed that, the soil pH value significantly decreased in Sº+T and Sº+VC+T treatments, in com\pared to the blank. While, the EC of these treatments significantly increased with respect to the blank. The results also showed that most of the treatments have been able to increase the solubility of the nutrients. However, the effect of Sº +VC+T treatment on increasing the availability of studied soil nutrients and decreasing pH value was more significant than the other treatments. Conclusion: Analysis of the results obtained from this study using classical statistic methods showed that applying a single treatment cannot remove all obstacles to increase nutrient availability in calcareous soils. This may be attributed to high buffering capacity of calcareous soils and complexity of factors which control mineral solubility and nutrient availability. While, treatments that simultaneously provide soil organic matter and lower pH (such as Sº+VC+T) can significantly remove barriers to increase nutrient uptake in these soils. As a result, the simultaneous application of organic fertilizers, elemental sulfur and Thiobacillus bacteria can be a promising approach to increase the solubility of nutrients in calcareous soils and to increase the quantitative and qualitative growth of plants in these soils.
Research Article
Z. Dianat Maharluei; M. Fekri; M. Mahmoodabadi; A. Saljooqi; M. Hejazi
Abstract
Introduction: Today, soil pollution is an important environmental issue that should be taken into account. Industrial activities cause pollution and accumulation of heavy metals in the soil. Soil pollution significantly reduces the quality of the environment and threatens human health. Heavy metals are ...
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Introduction: Today, soil pollution is an important environmental issue that should be taken into account. Industrial activities cause pollution and accumulation of heavy metals in the soil. Soil pollution significantly reduces the quality of the environment and threatens human health. Heavy metals are one of the most important pollutants in the environment, which has received a lot of attention in recent decades. Heavy metal pollution is a serious problem in developing countries and urban areas. Among heavy metals, lead is found in large amounts in the Earth's crust, which has several effects on human health and the environment. Lead is an essential element for the plant and one of the most important pollutants, which is toxic even at very low concentrations. Its presence in the culture medium has a negative effect on germination rate, water status in the plant, dry root weight and aerial part of the plant, photosynthesis, absorption of nutrients and enzymatic activity. Much research has been done to use alternative and modern methods to clean the environment of heavy elements. One way to stabilize heavy metals in the soil is to use biochar. Due to its cation exchange capacity and high specific surface area, biochar is able to reduce the pollution caused by organic pollutants and heavy metals, stabilize heavy metals and improve the condition of plants and soil in terms of pollution. The aim of this study was to investigate the effect of modified biochars rice husk and almond soft husk on lead desorption kinetics in contaminated calcareous soil. Materials and Methods: To conduct this research, a sufficient amount of soil from a depth of zero to 30 cm was collected from the farm of Shahid Bahonar Agricultural College in Kerman. Physical and chemical properties of the studied soil were measured after air drying and passing through a 2 mm sieve. To prepare the biochars (rice husk and almond soft husk), the residues, after collection, were air-dried and ground and then packaged in aluminum foil to limit the oxygenation process. They were then placed in an oven at 500 0C for four hours to produce a charcoal called biochar. Also, to prepare the modified biochar (NaOH and HNO3), one gram of biochar was added to 100 ml of distilled water and then 10 ml of concentrated acid (or 10 g of alkali) was added to it. Stirring at 60 0C for 24 hours. Finally, it was filtered using a centrifuge and washed several times with distilled water to neutralize the pH. The produced powder was dried at 70 0C for 24 hours. The lead desorption kinetics experiment was studied at several times (5, 15, 30, 60, 120, 240, 480, 960, 1440 and 2880 minutes) in two levels of biochar (0 and 4 wt %) and three levels of lead (0, 300 and 600 mg kg-1), which were incubated for 5 months under field moisture in a greenhouse. Results and Discussion: The kinetics results showed that the desorption of lead has the same pattern in all the time studied. Early rapid desorption occurred in the early desorption times (initial 30 minutes) followed by low-velocity desorption (8 hours) and finally, equilibrium was observed in the treated and control samples. The significant difference between the amount of lead released from the treated soils and control indicated a positive effect of both used engineered biochars on reducing lead desorption. The highest amount of lead desorption was observed in soil without biochar, while the lowest desorption rate occurred in treatments of rice husk and almond soft husk modified by sodium hydroxide. The application of modified biochar rice husk highly reduced lead desorption, compared to modified biochar almond soft husk. Conclusion: According to the results, the modified biochar with sodium hydroxide caused a significant reduction in lead desorption compared to other treatments, and this reduction was more in biochar rice husk than the almond soft husk one. It can be stated that rice husk biochar has been more successful than almond soft husk biochar due to its more porous structure and cation exchange capacity. Among the equations used for lead desorption estimation, the two-constant rate equation was selected as the best model for data fit due to high explanatory coefficient (R2) and low standard error (SE). According to the above, the use of biochar can be recommended as a modifier in lead contaminated soils.
Research Article
Rasoul Mirkhani; A.R. Vaezi; hamed rezaei
Abstract
Introduction: Awareness of the physical, chemical and biological quality of soil in agriculture and natural resources is essential for optimal land management and achieving maximum economic productivity. Soil has various functions, including crop production ability, carbon storage, water retention, nutrient ...
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Introduction: Awareness of the physical, chemical and biological quality of soil in agriculture and natural resources is essential for optimal land management and achieving maximum economic productivity. Soil has various functions, including crop production ability, carbon storage, water retention, nutrient cycling, water filtering and etc. Thereby, the quality of soils can be taken into consideration depended on the purpose of their use. The soil quality indices are often regional; therefore, a set of indices cannot be used consistently to determine soil quality in all areas. In this study, the Nemero Soil Quality Index (NQI), the Weighted Additive Soil Quality Index (SQIw), and the Additive Soil Quality Index (SQIa) were determined using the total data set (TDS) and minimum data set (MDS) and the impact of properties affecting the soil quality and the yield of irrigated wheat were investigated, in Nazarabad region. Materials and Methods: This study was carried out in 26000 hectares of Nazarabad agricultural lands, known as an area with irrigated farms in western Alborz province. The Nazarabad area was sub-divided into a network consisting of 95 squires of 1650 m × 1650 m. The surface soil (0-30 cm) was sampled from the farms located in the middle of each squire (9+5 soil samples from 95 farms) and the irrigated wheat was sampled from 32 farms. Then, soil physical properties including sand, silt, and clay percentages, soil structural stability (MWD), bulk density (BD), particle density, soil porosity (F), field capacity (FC) and permanent wilting point (PWP), available water (AW), saturated hydraulic conductivity (Ks) and soil chemical properties including salinity (EC), pH, organic matter (OM), equivalent calcium carbonate (TNV), available phosphorus )p < sub>ava(, available potassium )Kava(, sodium absorption ratio (SAR) and soil microbial respiration (SMR) were measured. Effective properties on soil quality were selected using SPSS 24 by principal component analysis method (PCA). For this purpose, components with Eigen values greater than one were selected and in each component, properties with high loading coefficient up to 10% lower than the highest loading coefficient were selected MDS affecting soil quality. Then, the Nemero Soil Quality Index (NQI), the Weighted Additive Soil Quality Index (SQIw) and Additive Soil Quality Index (SQIa) were determined using TDS and MDS. For validating soil quality indices, the correlation between the yield of irrigated wheat and NQI, IQIa and IQIw indices were determined in MDS and TDS. Results and Discussion: The results showed that the correlation between the soil quality indices (NQI, SQIw and SQIa( using total data set and MDS were significant (p <0.01). In addition, a significant correlation was observed between methods of MDS and TDS in IQIw (r=0.76), IQIa (r=0.73) and NQI (r=0.68) indices. According to the results, there was a significant correlation (p <0.01) between the yield of irrigated wheat and IQIw (r=0.68), IQIa (r=0.67) and NQI (r=0.62) using MDS method; and using total data set method this correlation was 0.61, 0.58 and 0.58, respectively. The results indicated that using NQI, SQIw and SQIa indices based on MDS, 42, 57 and 57% of the study area were in very high quality category and 29, 25 and 24% were in high quality category, respectively. However, using NQI, SQIw and SQIa indices based on TDS, 16, 16 and 18% of the study area were in very high quality class and 42, 39 and 45% were in high quality class, respectively. Conclusion: The results showed that in Nazarabad region, the yield of irrigated wheat was affected by texture, p < sub>ava, B, SAR, Bd and TNV. There was no significant difference between IQIw and IQIa and NQI indices. In addition, the correlation between soil quality indices based on MDS and total data set was significant, and the correlation between the yield of irrigated wheat and the soil quality indices was stronger while using MDS rather than the use of TDS. Therefore, the use of MDS is more appropriate due to better results and fewer properties and less cost. According to the results obtained from Nazarabad region using NQI and SQIw indices, nearly 82% and 72% of the area are in the very high and high quality class, about 6% and 8% are in the moderate quality class and about 7% are in very low and low quality class, respectively. The studied area is less restricted in terms of physical properties such as soil texture and bulk density. Consequently, due to the high quality of soils in Nazarabad region, it is possible to improve the yield of wheat by proper management.
Research Article
B. Mirkamandar; Seied Hosein Sanaei-Nejad; H. Rezaee-Pazhand; M. Farzandi
Abstract
Introduction: The behavior of daily changes in temperature is not straightforward. We first drew the curve of this variable on a normal day. It can be seen that the distribution of this variable was not normal. The curve of this variable was a skewed curve to the right. Therefore, the equal coefficients ...
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Introduction: The behavior of daily changes in temperature is not straightforward. We first drew the curve of this variable on a normal day. It can be seen that the distribution of this variable was not normal. The curve of this variable was a skewed curve to the right. Therefore, the equal coefficients could be used only as approximation for estimating daily average temperature. Climatic conditions of the meteorological stations were also another parameter to be considered. This research presents a new method for estimating daily average of temperature in three climatic regions of Iran. The patterns for the sample stations in each climatic region were presented separately. Materials and Methods: E. Eccel (2012) developed algorithms to simulate the relative humidity of the minimum daily temperature in 23 weather stations in the ALP region of Italy. In this research, the base pattern was calibrated by temperature and precipitation measurement. Ephrath, et al. (1996) developed a method for the calculation of diurnal patterns of air temperature, wind speed, global radiation and relative humidity from available daily data. During the day, air temperature was calculated by: (1) (2) where S (t): Dimensionless function of time, DL: Day Length h, LSH: the time of maximum solar high h, ta: Current air Temperature, P: the delay in air Tmax with respect to LSH h. Farzandi, et al. (2012) presented more accurate patterns for estimating daily relative humidity from humidity of Iranian local standard hours and daily precipitation variables, the minimum, maximum and average daily temperature in coastal regions. The purpose was to present linear and nonlinear patterns of daily relative humidity separately for different months (12 patterns) and annually in coastal regions (the Caspian Sea, the Persian Gulf, and the Oman Sea). Rezaee-Pazhand, et al. (2008) introduced new patterns for estimating daily average temperature in arid and semiarid regions of Iran. Final pattern has interception and new coefficients for estimate daily average of temperature. (3) Veleva, et al. (1996) showed that the atmospheric temperature-humidity complex (T-HC) of sites located in a tropical humid climate cannot be well characterized by annual average values. Better information is given by the systematic study of daily changes of temperature (T) and relative humidity (RH), which can be modeled with linear and parabolic functions. Farzandi et al. (2011) divided Iran into three climatic clusters used in the present work. First a classification which provides climatological clustering. This clustering was used the data of annual relative humidity, temperature, precipitation, altitude, range of temperature, evaporation and three indices of De Martonne, Ivanov and Thornthwaite. Iran was partitioned into three clusters i.e. coastal areas, mountainous range and arid and semi-arid zone. Several clustering methods were used and around method was found to be the best. Cophenetic correlation coefficient and Silhouette width were validation indices. Homogeneity and Heterogeneity tests for each cluster were done by L-moments. The “R”, software packages were used for clustering and validation testes. Finally clustering map of Iran was prepared using “GIS”. The data of 149 synoptic stations were used for this analysis. Systematic sampling was done to select sample stations. The linear regression model was fitted after screening and data preparation. A model was presented for estimating daily average of temperature in each climatic region and sampling stations in each cluster. The best models were presented by reviewing the required statistics and analyzing the residuals. The calibration and comparison of the presented patterns in this paper with commonly applied models were undertaken to calculate the mean squared error. “SPSS.22” software was used for analysis. Results and Discussion: The coefficient of determination (R2) and the Fisher statistics show that the patterns have a good ability to estimate the daily average of temperature. The daily average temperature pattern confirmed an interception in the equations. Standardized coefficients showed that predictor variables were not weighted in all of the patterns. The average values of the residuals in each pattern was zero. According to the graphs, stabilization of variance can be seen based on the residual on each pattern in each cluster. The mean squared error is a measure of the applicability of patterns. The accuracy of the estimating daily average temperature by the recommended models in three climates was confirmed by calculating the mean squared error. The proposed patterns of this study had less error than common patterns. Thus, the patterns have a good ability to estimate daily average temperature. Conclusion: The maximum temperature in calculating daily average of temperature is more effective than the minimum temperature. The standardized coefficient (Beta) of the daily average temperature patterns in coastal cluster was 48.2% for the minimum temperature and 51.8% for the maximum temperature. The largest influence of the maximum temperature was 63.1% in mountainous cluster for estimating daily average temperature. Range of the interception in the equations was from -1.735 to 0.26. The independent assumption of the residual was confirmed with the acceptable value of Durbin-Watson statistics. The average of the residuals in each patterns was zero. According to the graphs stabilization of variance can be seen based on the residual on the each pattern in each cluster. The proposed patterns were calculated according to mathematical principles but the common patterns did not consider these mathematical principles. The mean squared error (MSE) of the proposed patterns are less than common patterns. Therefore, the patterns presented in this study are more powerful than common patterns. The largest difference between the proposed patterns and the common patterns for estimate the daily average of temperature was 24% in mountainous cluster. Climatic clustering was done for states. The monthly and annual average temperature can be reliably estimated by using the data of sample stations in each state. These findings can be used to estimate daily, monthly and annual average of relative humidity in three climates and sample stations. In addition, one can employ the method for estimating daily, monthly and annual average of relative humidity and temperature based on around climatological clustering of Iran and other stations. Annual relative humidity, temperature, precipitation, altitude, range of temperature, evaporation can also be applied to estimate daily, monthly and annual average of temperature and relative humidity more accurately.
Research Article
S.M. Farmanara; B. Bakhtiari; N. Sayari
Abstract
Introduction: Drought is an extreme climate effect and a creeping phenomenon which directly affects the human life. A drought analysis usually requires characterizing drought severity, duration and frequency (SDF). These characteristic variables are commonly not independent, so this phenomenon is a complex ...
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Introduction: Drought is an extreme climate effect and a creeping phenomenon which directly affects the human life. A drought analysis usually requires characterizing drought severity, duration and frequency (SDF). These characteristic variables are commonly not independent, so this phenomenon is a complex natural disaster and climate change makes it likely to become more frequent and immense in many areas across the world. Therefore, in drought analysis, it is needed to investigate its multivariate nature and spatial variability clearly. Copula, as a model of multivariate distribution, has been used widely in hydrological studies. As the standardized precipitation index (SPI) is more accessible than other indices, it is the most commonly used indicators for analyzing the SDF of meteorological drought. Here, the study has two major focuses: 1) Fitting drought characteristics from SPI to appropriate copulas, then using fitted copulas to estimate conditional drought severity distribution and joint return periods for both historical and future time periods in Fars province. 2) Inquiring the effects of climate change on the frequency and severity of meteorological drought. Materials and Methods: Among the weather stations of Fars province, six synoptic stations were selected, which had longer historical data than others. The data used included 24-hour precipitation during 15 (2004-2018) to 33 (1986-2018) years. Three steps were carried out. Stage one: downscaling of outputs of the large scaling (CanESM2) based on two intermediate (RCP4.5) and pessimistic (RCP8.5) scenarios using SDSM, ver. 4.2.9 during the period of 2020 to 2050. Stage two: calculation of SPIand drought characteristics in the base and future periods (2050-2020). Stage three: extracting SDF curves for the base and future periods under RCP4.5 and RCP8.5 scenarios using copula. The SPIwas used to extract the drought duration and drought severity in the Fars province using GCM models under two selected scenarios (RCP4.5 and RCP8.5) from the IPCC Fifth Assessment Report (AR5) scenarios. The gamble copula function was used to construct the joint distribution function for evaluating the drought return periods in the study area. Because short-term drought prediction is more practical than long-term prediction, we used the 1-month SPI for the copulas-based analysis. Drought severity and duration were calculated based on computed SPIvalues by using the past available data. Drought duration is defined as successive months with SPIvalue less than -1 and drought severity as the accumulative SPIvalue during the period with successive SPIvalue less than -1. The normal and log-normal functions were selected as the candidate distribution function for drought duration and drought severity. Results and Discussion: The results showed that the frequency of drought occurrence in the Fars province will increase during the period of 2020-2050 under the both two scenarios. In the RCP8.5 scenario, the duration of the drought will also increase. The increase and decrease of monthly rainfall in RCP 4.5 and RCP 8.5 were 2.8 and 6.5%, respectively.The duration of the drought were obtained to be 5.25, 5.5 and 6 days at Shiraz station, with a 2 and 5 years return period, in the baseline and future periods under RCP4.5 and RCP8.5 scenarios, respectively. These values were estimated to be 4, 3.5 and 5 days at Bavanat Station.It is expected that the precipitation will decrease at Shiraz station under the two scenarios.Similarly, this amount is expected to increase and decrease at Bavanet station in the RCP4.5 and RCP8.5 scenarios, respectively. Conclusion: Changing droughts based on climate change is important in many aspects. In this study, the performance of two-variable statistical distribution of severity and duration of drought was investigated based on the copula function. The comparison of the drought period calculated using the SPIshowed that due to the climate change, the frequency of drought periods is expected to increase in the base and future periods. The results showed that the value of the precipitation changes in the RCP8.5 scenario is higher than the RCP4.5 scenario. Generally, the performance criteria showed that the SDSM had a good performance for the past and the future periods in Fars province for precipitation data. It is expected that with consideration of the amendments in the sixth report of the IPCC, more precision can be obtained in precipitation modeling. Therefore, reviewing the output of the SDF curves with the availability of the results of this report is suggested.
Research Article
H. Mirhashemi
Abstract
Introduction: Potential evaporation is the result of the combined effects of several meteorological elements, including air temperature, relative humidity (or vapor pressure for saturation), wind speed, sunshine hours and air pressure. The amount of potential evaporation depends on how these variables ...
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Introduction: Potential evaporation is the result of the combined effects of several meteorological elements, including air temperature, relative humidity (or vapor pressure for saturation), wind speed, sunshine hours and air pressure. The amount of potential evaporation depends on how these variables interact in each climate region. Potential evaporation response of each of these variables depends on the importance that variable plays in the environment. For example, in windy places, the importance of wind speeds in the potential evaporation rate increases relative to places with calm air. By changing each of these meteorological elements, while the rest of the elements react to the given change, the overall effect of these changes and reactions is reflected in the amount of potential evaporation. It is therefore obvious that the potential evaporation response to meteorological variables due to spatial and time variations of these variables is of a complex nature. Materials and Methods: For this study, monthly data of air temperature, air pressure at sea level, wind speed, relative humidity and sunshine hours were used as independent variables and monthly data of evaporation pan at Tabriz Synoptic Station as response or dependent variable. In this study, firstly, the nonlinear and linear relationship between meteorological elements and potential evaporation were identified through Generalized Additive Model (GAM), MARSplines Model, and Generalized Linear Model (GLM), respectively. In the next step, by applying the simplex algorithm on the MARSplines model, the evaporation response gradient levels were determined individually for the meteorological variables. Also, to understand the process of pure evaporation response to each of these variables under different climatic conditions, first three weather conditions based on Tabriz Synoptic Station data were defined in three scenarios as S-1, S-2 and S-3. Then, by controlling and maintaining the meteorological variables under these three scenarios and combining the simplex algorithm with the MARSplines Model, the net evaporation reaction curves for the meteorological variables changes were evaluated. Results and Discussion: The computational results show that in all combinations, the computational error of the GAM model is less than the GLM model. Also considering the significant variables in each model, the combination of temperature, pressure, wind speed and sunshine are considered as the best subset of the effective variables in the distribution of potential evaporation in both models. On the one hand, relative humidity in these two linear and nonlinear models, in combination with other variables, does not show a significant relationship with potential evaporation. The results of the graphs of Splin smoothing components of the GAM model show that the overall effect of temperature on the evaporation is incremental. But the unit amount of this effect increases with increasing temperature. The individual evaporation reaction against air temperature is similar to its combined reaction. It is thus clear that other meteorological variables do not play a significant role in the influence of air temperature on the evaporation gradient. The overall and hybrid effect of air pressure variations on the amount of evaporation is singular and decreasing. Instead, the individual effect of this variable on evaporation is very intense, decreasing, and partly linear. Therefore, the major influence of air pressure on evaporation in the environment is due to the performance of other variables that interfere with the relationship between these two variables. The evaporation hybrid response to wind velocity was also incremental, although the single and nonlinear evaporation response to wind velocity was not significant, but its tendency was to increase its slope with respect to wind velocity changes. Sunny hours also have a net effect on the amount of evaporation. However, the slope of the solitary effect of this variable, like wind speed, is more than its combined effect. Based on the GLM model results, except for relative humidity, the other variables have a significant linear effect on the potential evaporation. Evaporation response to changes in meteorological variables under S-1, S-2 and S-3 scenarios, while accurately determining the interaction of these variables in plotting absolute evaporation, implicitly implying the synergistic role of these variables in determining absolute evaporation. The lowest distance between the absolute values of evaporation under these three scenarios is related to air temperature, which implies less influence of air temperature than the other variables. That is, the effect of each of the meteorological variables on the amount of evaporation depends to a large extent on the relationship of this variable to other meteorological variables, if such a matter is less weighted for temperature. Conclusion: The results of this study show that, except for air pressure, which has an increment-reducing effect on evaporation, other variables have only an incremental influence on evaporation and the intensity of this relationship has changed. This process has resulted in a nonlinear component in the relation of independent variables to evaporation. Since hybrid spline smoothing graphs determine evapotranspiration response to each of the predictor variables by eliminating the effect of other variables, therefore, consideration of the composition of these meteorological variables provides more accurate information on evaporation behavior against environmental changes. Through individually fitting evaporation against these meteorological elements, one cannot find how evaporation works against environmental changes. Comparing individual and combined evaporation responses to meteorological variables, while identifying the net effect of each of these variables, explains why evaporation responses within a given unit differ from changing meteorological variables over different times and locations.
Research Article
H. Asakereh; S.A. Masoodian; M. Darand; S. Zandkarimi
Abstract
Introduction: Studies of the atmosphere over the last hundred years have shown that human activities have caused changes in the atmosphere. The tropopause is one of the layers of the atmosphere whose changes have recently been introduced as a sign of a human impact on climate change. The height ...
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Introduction: Studies of the atmosphere over the last hundred years have shown that human activities have caused changes in the atmosphere. The tropopause is one of the layers of the atmosphere whose changes have recently been introduced as a sign of a human impact on climate change. The height of the tropopause is affected by its upper and lower layers (the stratosphere and troposphere). The results of the studies conducted by various researchers have shown that different factors affect the height of tropopause and its changes, which can be divided into two groups. The first group of natural factors (such as changes in solar radiation and weather due to volcanoes, etc.) and the second one is human factors (including changes in greenhouse gases, human-induced changes affecting the ozone of the stratosphere and the production of air vents from human resources, etc.). Thus, altitude tropopause is naturally influenced by spatial characteristics (e.g. latitude and altitude), time (such as the time of year and hours of the day) as well as the frequency of atmospheric actions that determine climatic conditions. Materials and Methods: Compared to the studies performed globally, a limited number of studies concerning the tropopause have been conducted in Iran. Moreover, the applied methods and the length of the dataset were often inadequate. Therefore, in the present study, the daily data of temperature, and geopotential height from the European Centre for Medium-Range Weather Forecasts (ECMWF) for 700 to 50 hpa with a spatial resolution of 0.25 × 0.25 longitude/latitude were applied from 1979 to 2018 for the detection of tropopause. Accordingly, 2491 cells covered across Iran. The LRT was used to detect tropopause. The tropopause is defined as ‘‘the lowest level at which the lapse-rate decreases to 2 ºC/km or less, provided that the average lapse-rate between this level and all higher levels within 2 km does not exceed 2 ºC /km”. In the present study, in addition to changing the position, changing the scale (variance) as well as the shape of the frequency distribution (skewness and elongation) of the tropopause pressure level in each of the pixels on Iran was investigated. To calculate skewness, and kurtosis, daily tropopause height data were used. For each of the months studied, diffraction, skewness, and elongation were extracted using daily data and finally using data during the 40 years. The extracted trends of variance, skewness, and kurtosis were examined for each month. To track the synchronicity and conformity of changes in altitude and trend of tropopause pressure level with the trend of changes in mean monthly temperature in the lower and upper levels of the tropopause and the trend of the temperature difference between the two layers around tropopause was also evaluated over 40 years. In order to evaluate the long-term trend of each of the studied indices (mean, variance, skewness, and kurtosis) in relation to the height and pressure level of the tropopause, linear regression method with least-squares error method was used. Results and Discussion: The results of the study of altitude trend and tropopause pressure level showed that in most of the months studied and in most parts of the country, the trend of changes in tropopause pressure level was not significant at the level of 95% confidence. According to the results obtained for the winter months, it was found that the trend of a tropopause pressure level in December had no statistical significance over Iran at a 95% confidence level. In January and February, the obtained trend was not statistically significant except for southeastern areas. In the summer months, unlike the winter months, the trend of tropopause pressure levels was significant in most regions. During the summer months, in areas where the trend was significant, the trend of tropopause pressure levels was positive. Examination of the trend of tropopause height in terms of meters showed different results with pressure level. During the winter months, the trend was positive in all regions, and in January and February, this trend was significant in many areas, while the summer months did not exhibit a significant tropopause. The results of examining the trend of the low temperature of the tropopause in summer and winter months showed that the observed trend was not statistically significant in December, but in other months, a positive and significant trend was detected. Examination of the temperature trend in the high level of tropopause also showed that the temperature trend in this part of the atmosphere, like the low level of the tropopause in large parts of the country in the studied seasons, lacked statistical significance. Examination of the trend of the temperature difference between high and low levels also showed that the trend of the temperature difference between these two levels was statistically insignificant at the majority of cases. The temperature difference trend of the two levels studied in the summer months was negative and significant at most regions. In other words, the decrease in the temperature difference between low and high tropopause in these two seasons and in some areas indicates a strong decrease in tropopause. Examination of the trend of variance, kurtosis and skewness also showed that the observed trend lacked statistical significance in the two studied chapters at most areas. There was also no relationship between the surface temperature trend and changes in tropopause height. Conclusion: The results of this study showed that tropopause had no statistically significant trend in most areas and months. Moreover, the significant trend was not related to the two temperatures around tropopause and surface temperatures.
