Research Article
Irrigation
M. Jamshidi Avanaki; , K. Ebrahimi; S.S. Hashemi
Abstract
IntroductionDrought, as an environmental crisis, not only impacts ecosystems but also poses risks to human activities and has significant negative effects. The occurrence of intermittent and prolonged droughts, along with significant fluctuations in climate, exacerbates water scarcity, particularly in ...
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IntroductionDrought, as an environmental crisis, not only impacts ecosystems but also poses risks to human activities and has significant negative effects. The occurrence of intermittent and prolonged droughts, along with significant fluctuations in climate, exacerbates water scarcity, particularly in surface water resources; thus, groundwater resources play a key role as a vital source for supplying water for various consumption needs.Groundwater drought is one of the serious and increasing challenges that has been acutely felt in recent years. Climate change and increasing water demand in agricultural and industrial sectors has led to increase dextraction from groundwater sources, significantly affecting many plains and groundwater resources in the country, resulting in severe depletion. This has consequently led to water crises and recurrent droughts. Therefore, understanding the relationship between drought and the status of groundwater resources is crucial. This issue not only impacts agriculture and food security but also has negative effects on public health, the economy, and the environment. For this reason, proper and sustainable management of these resources in the face of drought challenges is essential. Materials and MethodsThe examination of hydrogeological droughts and the monitoring of groundwater levels is essential for providing appropriate solutions for the protection and management of water resources.In the present study, the Groundwater Resource Index (GRI) was used to assess groundwater drought in the Qazvin Plain. Additionally, to explore the relationship between the GRI and the Standardized Precipitation Index (SPI) across different time scales, the correlation coefficient between the two indices was calculated. Subsequently, the GRI was localized within the plain by analyzing its values across various monitoring wells. Results and DiscussionThe high correlation between the GRI index and the SPI drought index over a 48-month timeframe indicated that groundwater resources in the Qazvin plain were influenced by both wet and dry weather phenomena, with a time lag of approximately three to six months before meteorological drought translated into groundwater drought. Eslamian et al. (2009) also reported a three-month time lag for the effects of drought on the groundwater resources of the Qazvin, Buin Zahra, and Hamadan plains in their research. ConclusionThe localization study of the GRI index in the Qazvin Plain region concluded that the index is highly responsive for assessing and evaluating groundwater drought. It effectively identified wet and dry years and showed a strong alignment with the behavior of the groundwater table. The analysis of drought during the years from 1996-2001 also illustrated that the impacts of drought continued into subsequent years on groundwater resources, and according to the GRI index, the decline in groundwater levels persisted in later years. This was evident even with increased precipitation in 2002 and thereafter, where we continued to witness declines and the ongoing trend of groundwater drought. AcknowledgmentsWe would like to thank the University of Tehran and the Water Resources Management Company of Iran for providing the necessary facilities to conduct this research study and prepare relevant papers.
Research Article
Soil science
S.S. Hosseini; F. Rejali; P. Keshavarz
Abstract
Introduction
Water scarcity is a major challenge in Iran, with annual rainfall averaging 235 to 260 mm, only a third of the global average. Wheat, a staple crop in Iran, faces severe yield reduction under drought conditions. Utilizing biofertilizers like plant growth-promoting rhizobacteria ...
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Introduction
Water scarcity is a major challenge in Iran, with annual rainfall averaging 235 to 260 mm, only a third of the global average. Wheat, a staple crop in Iran, faces severe yield reduction under drought conditions. Utilizing biofertilizers like plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal (AM) fungi could help enhance water use efficiency (WUE) and yield in such environments. However, the effectiveness of biofertilizers varies based on several factors, including the type of biofertilizer (bacterial or fungal), the strain or species used, and the formulation (solid or liquid). Despite the established benefits of both PGPR and AM fungi in enhancing drought tolerance and WUE, there is a lack of comparative studies that examine the specific performance of bacterial versus fungal biofertilizers and their formulations under varying levels of water stress. Thus, the objectives of this study are as follows: 1) to identify the most suitable type of biofertilizer (bacterial or fungal) for improving wheat yield and WUE under drought conditions in Mashhad's climatic conditions; 2) to determine the effect of ACC deaminase enzyme on the efficiency of PGPR in enhancing wheat yield and WUE; 3) to compare the performance of AM fungal biofertilizers in two formulations (powder and liquid) and between single-species and multi-species inoculants.
Material and Methods
The experiment was conducted as a split-plot design with three replicates, where irrigation levels constituted the main plots, and biofertilizer treatments formed the subplots. The irrigation treatments included full irrigation (100% of wheat’s water requirement), mild drought stress (85%), and severe drought stress (65%). The biofertilizer treatments were: no biofertilizer (F1), serving as a control; Pseudomonas fluorescens producing ACC-deaminase (F2); P. fluorescens without ACC-deaminase (F3); AM fungi (Rhizophagus irregularis) in liquid form (F4); and (5) AM fungi (R. irregularis, Funneliformis mosseae, and Claroideoglomus etunicatum) in powdered form (F5).
Results and Discussion
Both irrigation levels and biofertilizer types had significant impacts on root colonization, yield, and WUE. Reducing irrigation from 100% to 85% and 65% of crop water requirements significantly reduced root colonization across all treatments. Among the bacterial treatments, only P. fluorescens producing ACC-deaminase (F2) showed a significant positive effect under severe drought (65% irrigation). This treatment increased grain yield by 9%, biological yield by 7%, and WUE by 6.8% compared to the control (F1). The presence of ACC-deaminase likely contributed to mitigating the effects of drought-induced ethylene, promoting better root growth and nutrient uptake under water stress. In contrast, P. fluorescens without ACC-deaminase (F3) did not significantly improve yield or WUE, emphasizing the importance of ACC-deaminase in promoting drought tolerance. Fungal biofertilizers outperformed bacterial treatments in grain and biological yield, as well as WUE. Under severe drought, powdered AM fungi (F5) increased grain yield by 26% and biological yield by 21% compared to the control, and WUE based on grain yield improved by 26%. This superior performance of AM fungi, particularly in powdered form, can be attributed to their ability to enhance nutrient and water uptake under drought conditions. These findings corroborate earlier studies that demonstrated AM fungi's ability to improve crop yield and WUE under drought stress by enhancing water uptake, nutrient availability, and improving the plant's physiological responses, such as maintaining cell membrane stability and increasing antioxidant activity. The powdered formulation of AM fungi (F5) showed greater effectiveness than the liquid form (F4). The higher colonization rates and performance in yield improvement may be due to the inclusion of multiple fungal species in the powdered form. The performance differences between the liquid and powdered AM fungi formulations may also be influenced by the physical properties of the biofertilizer since powdered inoculants are most effective when applied to the seeds of grasses like wheat and barley, as the structure of these seeds allows for better adhesion of the powder.
Conclusion
In conclusion, among the bacterial biofertilizers, only P. fluorescens producing ACC-deaminase significantly enhanced plant performance under severe drought, underscoring the importance of ACC-deaminase in alleviating drought stress. However, fungal biofertilizers, especially in powdered form, were more effective overall in improving yield, biological productivity, and WUE under varying levels of water stress. This research confirms that the application of AM fungi can serve as an effective strategy for improving wheat yield and increasing WUE in the climatic conditions of Mashhad. Overall, the observed differences in the effectiveness of these biofertilizers suggest that the appropriate selection of both type and formulation of biofertilizers can significantly contribute to managing water stress and improving crop production.
Research Article
Soil science
N. Khalili; R. Ghorbani Nasrabadi; M. Barani Motlagh; R. Khodadadi
Abstract
Introduction
Actinobacteria are one of the most abundant microbial groups in soil and play a crucial role in preserving ecosystems. They are among the soil microbial groups capable of releasing phosphorus from low-soluble or insoluble phosphorus sources, which enhances plant growth. Their application ...
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Introduction
Actinobacteria are one of the most abundant microbial groups in soil and play a crucial role in preserving ecosystems. They are among the soil microbial groups capable of releasing phosphorus from low-soluble or insoluble phosphorus sources, which enhances plant growth. Their application in agricultural systems is recognized as an environmentally friendly strategy to limit the negative effects of chemical inputs and improve the availability of nutrients, especially phosphorus, in the rhizosphere. Additionally, humic acid, as an organic growth stimulant, plays an important role in improving soil fertility and biological communities, and its combined use with actinobacteria increases the efficiency of fertilizer use, particularly phosphorus-based fertilizers. Therefore, the aim of this research was: (i) to screen the phosphorus solubilization potential of actinobacteria isolates at different incubation times, (ii) to investigate the effect of adding humic acid on the phosphorus solubilization capacity actinobacteria isolates under laboratory conditions, and (iii) to monitor the impact of selected actinobacteriun isolate and humic acid, at various phosphorus fertilizer levels, on soil phosphorus content, plant phosphorus uptake, and some biochemical properties of the soil.
Materials and Methods
In this study, five actinobacteria isolates, collected and purified from various agricultural, orchard, and rangeland ecosystems of Golestan Province, were screened based on their morphological characteristics. These strains were utilized for screening purposes. To prepare fresh cultures of the actinobacteria isolates, they were subcultured on solid yeast extract-malt extract agar medium. The effects of incubation time and the application of humic acid on the phosphate solubilization ability of the actinobacteria isolates were then investigated. This experiment was conducted in a factorial arrangement within a completely randomized design, with the following factors. To examine the effect of the selected superior actinobacterium isolate and its interaction with different phosphorus levels and humic acid application, a factorial pot experiment was conducted in a completely randomized design. The experimental factors included a mineral phosphorus source at three levels (control, 20 kg, and 40 kg of phosphorus per hectare from monoammonium phosphate), Streptomyces inoculation at two levels (control and inoculation with the selected isolate), and humic acid application at two levels (control and 2 mg per kg). The experiment was carried out on maize (Single Cross 704) with three replications. For seed preparation, a sufficient number of healthy maize seeds were selected and surface sterilized by immersing them in alcohol for 30 seconds. They were then exposed to 5% sodium hypochlorite for 2 to 3 minutes, followed by rinsing eight times with sterile distilled water. To prepare the microbial inoculum, the selected superior isolate was grown in yeast extract-malt extract medium at an appropriate (107 CFU/mL). The seeds were then placed in pots, and one milliliter of the Streptomyces suspension was applied to the seeds for inoculation. At the end of the experiment, the phosphorus content in the soil and plant, as well as the soil biochemical responses were measured.
Results
Based on the results obtained from this study, the application of humic acid led to an increase in microbial biomass and enhanced phosphorus release by actinobacteria isolates under laboratory conditions. As the incubation period extended from 7 to 14 days, the solubility of phosphate showed an increasing trend. The results showed that the highest phosphorus content in the soil was associated with the combined application of a high phosphorus level (40 mg per kg) along with humic acid and Streptomyces inoculation. Analysis of microbial biomass phosphorus revealed that the highest level was related to the treatment combining the highest level of phosphorus fertilizer and humic acid. According to the findings related to phosphatase enzymes, the combined application of the Streptomyces treatment, humic acid, and phosphorus resulted in an increase in the levels of these enzymes. Additionally, the results of microbial respiration in the soil indicated that the combined treatment of Streptomyces and the highest level of phosphorus fertilizer enhanced microbial respiration in the soil. The phosphorus content in the plants under the combined treatments of Streptomyces, humic acid, and phosphorus showed that the integration of Streptomyces inoculation and humic acid was effective in improving soil phosphorus availability and led to an increase in the phosphorus content of the plants. The results of this study showed that inoculation with the selected Streptomyces isolate, along with the combined application of humic acid, enhanced the efficiency of phosphorus fertilizer utilization, making it more readily available to the plant.
Conclusion
In general, the results of current study revealed that the simultaneous application of humic acid and Streptomyces inoculation led to an increase in the availability of phosphorus in the soil and the phosphorus content in the plants, as well as an improvement in the biochemical responses of the soil. However, field experiments are necessary to confirm its effectiveness.
Research Article
Soil science
E. Fathi; M. Ekhtesasi; A. Talebi; J. Mosaffaie
Abstract
IntroductionWatersheds, as diverse ecosystems, play a fundamental role in water provision, soil conservation, biodiversity, and ecological sustainability. In addition to delivering environmental services, these areas serve as vital resources for supporting the livelihoods and well-being of local communities. ...
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IntroductionWatersheds, as diverse ecosystems, play a fundamental role in water provision, soil conservation, biodiversity, and ecological sustainability. In addition to delivering environmental services, these areas serve as vital resources for supporting the livelihoods and well-being of local communities. However, population growth, climate change, land-use changes, and overexploitation have imposed significant pressures on these ecosystems, jeopardizing their health and natural functionality. The degradation of these areas can lead to serious consequences for water resources, biodiversity, and environmental sustainability. Therefore, identifying and implementing effective strategies to preserve and enhance watershed health is essential. In this regard, the present study utilizes the strategic SWOT model to identify the strengths, weaknesses, opportunities, and threats within the Ilam Dam watershed and aims to propose practical solutions for improving and strengthening the health of these valuable ecosystems. Materials and MethodsTo achieve optimal strategies for resource management and improving the health of the study area, the SWOT analysis method was employed. This method provides a comprehensive framework for developing operational strategies by identifying existing strengths, weaknesses, opportunities, and threats. Data for this research were collected through field studies, specialized interviews with local experts, and a review of scientific resources and available information. To enhance accuracy and reliability in evaluating and weighting internal and external factors, the Analytic Hierarchy Process (AHP) and Expert Choice software were utilized. Subsequently, the collected data were analyzed using the Internal Factor Evaluation (IFE) and External Factor Evaluation (EFE) matrices, leading to the formulation of appropriate strategies. These strategies were categorized into four main types: aggressive, conservative, competitive, and defensive. Finally, to ensure the selection of the best options, the Quantitative Strategic Planning Matrix (QSPM) was applied. At this stage, each strategy was scored and prioritized based on its attractiveness and feasibility, ensuring the identification of the most effective and actionable strategies. Results and DiscussionAccording to the results of this study, seven factors were identified as strengths and seven as weaknesses (internal factors), along with seven opportunities and seven threats (external factors). The total score for strengths was 3.33, and for weaknesses, it was 3.57. Additionally, the score for opportunities was calculated at 3.54, while threats scored 3.28. Based on these scores and the internal and external factors evaluation matrix analysis, the WO strategy position was recommended, with specific solutions determined for each strategy. In the SO strategy, the QSPM matrix analysis indicated that optimal management of surface and groundwater resources, along with the establishment of suitable infrastructure for water capture and storage (strategy SO2), was recognized as the top priority. Within the ST strategy, the strategy of leveraging high organizational and local capacity to address the negative impacts of climate change and sustainably engage stakeholders and local communities in decision-making and watershed resource protection (strategy ST4) was prioritized. For the WO strategy, enhancing water and soil conservation programs and developing research and management initiatives through encouragement, support, and both material and spiritual contributions for specialized studies (strategy WO2) was identified as the main priority. Likewise, under the WT strategy, expanding and diversifying educational programs, developing educational content on water crises and climate change, and addressing the consequences of natural resource degradation in the basin, along with planning and approving national and international projects on climate change and dust storm mitigation (strategy WT1), emerged as the top priority. These strategies can provide an effective framework for improving resource management in watersheds and addressing environmental challenges. Conclusion The findings of this study clearly demonstrate that strengthening protective, managerial, and educational programs plays a crucial role in improving the health of this watershed. These strategies, by optimizing available opportunities and minimizing weaknesses, can significantly contribute to sustainable development and effective natural resource conservation. In particular, the implementation of these programs requires collaboration and synergy among the local community, governmental and non-governmental organizations, and related agencies. It is recommended that conservation and management planning be accompanied by education and awareness initiatives for the local community, so residents understand the importance of preserving natural resources and are encouraged to participate in conservation efforts. This active community involvement not only enhances the effectiveness of these strategies but also contributes to achieving desirable outcomes and ecosystem sustainability, setting the stage for more effective management and long-term conservation of water and soil resources.
Research Article
Soil science
Z. Movahedi Rad; M. Hamidpour; A. Tajabadipour
Abstract
Introduction
Recently, layered double hydroxides (LDHs) with a unique structure and unbeatable characteristics have been widely studied and investigated in various fields. One of these fields is the investigating the potential of these compounds to supply essential nutrients for plants. Several studies ...
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Introduction
Recently, layered double hydroxides (LDHs) with a unique structure and unbeatable characteristics have been widely studied and investigated in various fields. One of these fields is the investigating the potential of these compounds to supply essential nutrients for plants. Several studies have reported the application of LDHs as fertilizers for macronutrients and micronutrients. These compounds have a very high potential as fertilizers and can increase agricultural productivity. Micronutrients such as Zn, Cu and Mn can be structurally incorporated in the metal hydroxide layer. According to recent research, LDHs have shown a suitable potential to release micronutrients. However, more studies are needed to enhance our understanding of the mechanism and reaction of layered double hydroxides in different conditions. Although various studies have explored the potential of LDHs as slow-release fertilizers, our research focuses on the role of citric acid and tartaric acid and as well as the ratio of divalent to trivalent cations on the kinetics of Zn, Mn and Mg release from Mg-Zn-Mn-Al-LDH intercalated with nitrate.
Materials and Methods
All chemicals used in this study including citric acid (C6H8O7.H2O), tartaric acid (C4H6O6) KCl, Zn (NO3)2.6H2O, Mn(NO3)2.4H2O Mg(NO3)2.6H2O and Al(NO3).9H2O were of analytical grades, purchased from Chem-Lab or Merck Chemical Corporations. Solutions were prepared using decarbonated ultrapure water (electrical resistivity = 18 MΩcm). The LDHs were synthesized by co-precipitation method at constant pH = 9.2-9.6. Two types of LDHs were synthesized by varying the M+2(Zn+Mn+Mg)/M+3(Al) ratios of 3:1 and 4:1 in the precursor solution while stirring vigorously in a nitrogen atmosphere. The pH was kept at 9.2-9.6 by adding volumes of 3 M NaOH. The LDH crystals were allowed to ripen in the mixture for 2 hours, after which the precipitates were centrifuged at 3000 rpm for 20 min and washed several times with distilled water and placed in an oven at 70°C for 8 hours to dry.
The chemical composition of the synthesized layered double hydroxides (LDHs) was analyzed using furnace atomic absorption spectrophotometry (SavantAA, GBC) following acid digestion. The physical, chemical, and morphological characteristics of the LDHs were assessed through several techniques, including X-ray diffraction (Panalytical X Pert Pro X-ray diffractometer), field emission scanning electron microscopy (FE-SEM, Sigma VP), Fourier-transform infrared spectroscopy (FT-IR, Nicolet iS10 spectrometer), and Brunauer-Emmett-Teller (BET, BELSORP Mini II) analysis.
A batch study was conducted to evaluate the effects of varying M²⁺/M³⁺ ratios in LDHs and the influence of citric acid and tartaric acid on the release of Zn, Mn, and Mg from LDH (3:1) and LDH (4:1). In brief, 0.01 g of synthesized LDH was placed in a centrifuge tube and mixed with 10 ml of background electrolyte (0.01 M KCl) and 1.25 mM of citric acid or tartaric acid, maintaining an initial pH of 6–7 at a constant temperature of 25 ± 0.5 °C. Blank samples (without ligands) were also included for comparison. The suspensions were shaken for time periods ranging from 5 to 720 minutes at an agitation speed of 180 rpm. After shaking, the supernatant was separated by centrifugation at 4000 rpm for 20 minutes. The concentrations of Zn, Mn, and Mg in the supernatant solutions were determined using graphite furnace atomic absorption spectrophotometry.
To describe the time-dependent release of Zn, Mn, and Mg, several kinetic models were tested. Among the five models evaluated, the pseudo-second-order and power function models provided the best fit for the kinetic data. Additionally, the chemical species present in the initial solution and the saturation index (SI) of various minerals were predicted using the Visual MINTEQ 3.1 computer code.
Results and Discussion
The results indicated that the calculated molar ratio of divalent cations to trivalent cations closely matched the molar ratios used in the synthesis of the layered double hydroxide (LDH) samples. The X-ray diffraction (XRD) patterns for both LDH (3:1) and LDH (4:1) samples exhibited strong and sharp peaks corresponding to the 003 and 006 reflections, confirming the layered structure of the synthesized materials. Fourier-transform infrared (FT-IR) spectroscopy revealed two significant absorption bands around 3480 cm⁻¹ and 1620 cm⁻¹ in all synthesized LDH materials, which are indicative of stretching vibrations associated with the O-H groups in the hydroxide layers and the interlayer water molecules. Additionally, a sharp band at approximately 1382 cm⁻¹ in LDH (3:1) and a band at around 1354 cm⁻¹ in LDH (4:1) were attributed to the antisymmetric stretching mode of the nitrate anion present in the LDH structure. The specific surface areas of LDH (3:1) and LDH (4:1) were measured at 5.50 m²/g and 16.54 m²/g, respectively. Correspondingly, the average pore diameters were found to be 1.92 nm for LDH (3:1) and 2.55 nm for LDH (4:1), indicating differences in porosity between the two samples. The time-dependent cumulative release of Zn, Mn, and Mg from LDH (3:1) and LDH (4:1) in the presence and absence of citric acid and tartaric acid was investigated. The release of these micronutrients was accelerated in the presence of both organic acids. The release process appeared to occur in two stages: during the initial stage (0 to 50 minutes), the release rate of Zn, Mn, and Mg was rapid, followed by a period from 50 to 720 minutes where the release rate either fixed or slightly increased.
In this research, among the non-linear models which were used to determine the release kinetics of Zn, Mn, and Mg, the one with the highest R2 values was chosen. The R² values ranged from 0.81 to 0.99 for the pseudo-first-order model, 0.89 to 0.93 for the pseudo-second-order model, 0.97 to 0.99 for the Elovich model, 0.89 to 0.99 for the power function model, and 0.55 to 0.86 for the parabolic diffusion model. Ultimately, the pseudo-second-order and power function models were chosen to analyze the kinetic data. The amount of Zn, Mn and Mg released at equilibrium (qe) were higher in the presence of citric acid (42%) compared to tartaric acid. Additionally, the release of these elements was greater from LDH (4:1) than from LDH (3:1). This suggests that increasing the ratio of divalent cations to trivalent cations reduces the stability of LDH, enhancing the release of micronutrients.
Conclusion
The results of this study demonstrated that the release of Zn, Mn, and Mg from layered double hydroxides (LDHs) was influenced by time, the type of low molecular weight organic acid, and the ratio of divalent to trivalent cations in the LDH structure. Kinetic modeling revealed that the release rates of Zn, Mn, and Mg from LDH with a 4:1 ratio were higher than those from LDH with a 3:1 ratio. Additionally, the dissolution rates of LDHs were faster in the presence of citric acid compared to tartaric acid. To further assess the potential of LDHs as slow-release micronutrient fertilizers in calcareous soils, additional greenhouse and soil experiments are recommended.
Research Article
Soil science
A. Ansori Savari; , M. Nabipour; M. Farzaneh
Abstract
IntroductionThe high water demand of sugarcane in arid and semi-arid regions, combined with declining rainfall, has led to increased use of drainage water as a strategy for sustainable production management. It has been estimated that 20% of all cultivated land and 33% of irrigated agricultural land ...
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IntroductionThe high water demand of sugarcane in arid and semi-arid regions, combined with declining rainfall, has led to increased use of drainage water as a strategy for sustainable production management. It has been estimated that 20% of all cultivated land and 33% of irrigated agricultural land are affected by high salinity. Salinity stress poses two main threats to plants: ionic toxicity and osmotic stress. Ionic toxicity occurs when there is a significant accumulation of Na⁺ in plant leaves under saline conditions. This disrupts the balance of water and ions, damages organelle structures, inhibits growth, and can ultimately lead to plant death. Some studies have shown that ion toxicity caused by Na+ can inflict more irreversible damage on plants than osmotic stress. Silicon application (Si) showed improved photosynthetic efficiency, growth, and yield compared to plants under salt stress. Previous studies have also shown that silicon treatments can increase salinity tolerance in various plants, including wheat, corn, rice, and canola. However, the extent of silicon-mediated benefits under salinity can vary greatly between species and is largely dependent on the plant's capacity for element uptake dictated by its genetic makeup. There is limited information regarding the use of drainage water in sugarcane irrigation management in arid and semi-arid regions, as well as the potential for improving salinity stress through silicon application. Therefore, this study was conducted to evaluate the effects of Si on two sugarcane varieties irrigated with salt water. Materials and MethodsThe pot experiment was conducted in a greenhouse under natural light at the agricultural site of Sugarcane Dehkhoda Company in Khuzestan Province, Iran, in 2021-2022. The temperature and humidity percentages are indicated in Figure 1. This study was carried out as split-split plot design based on randomized Block design (RBD). The main plot factors included three levels of salinity: control of 1.4±0.2 dS.m-1 (S0) from the river water source, salinity stress of 4.1±0.2 dS.m-1 (S1), and salinity stress of 8.2±0.2 dS.m-1 (S2) from the drain water source, with a sub-factor of variety treatment (CP73-21 and CP69-1062). The silicon application timing was also considered as a sub-factor, with four levels: Si0, non-silicon application (Control); Si1, one month before salinity stress; Si2, during salinity stress; and Si3, after 30 days of salt stress, silicon was applied. The sugarcane sprouts are grown in polyethylene pots 100 cm in height and 45 cm in width. Each pot contained 100 kg of soil. A total of 216 experimental units were used during the experiment. The experimental pots were filled with a mixture of field soil and sugarcane filter cake in a 3:1 ratio. The results of the chemical analysis of field soil and filter cake are presented in Table 2. The salt stress was applied 113 days after growing cuttings and continued until harvest. Results and DiscussionThe results of the first year showed that salt stress significantly reduced the height of the sugarcane stalk. Also, at the salinity stress levels of 4.1 and 8.2 dS/m, the SPAD index decreased by 22.3% and 27%, respectively. Additionally, leaf sheath moisture dropped by 6.4% and 11.8%, electrolyte leakage increased by 11% and 22.7%, and the photosynthesis rate decreased by 28% and 42% compared to the control treatment. The optimal time to apply silicone fertilizer was one month prior to the onset of stress, which resulted in a significant improvement in all studied traits at salinity stress levels of 1.4 dS/m (control) and 4.1 dS/m. Furthermore, the qualitative analysis of sugarcane syrup in the second year revealed a decrease in sucrose percentage (14.1% and 33.5%, respectively) and white sugar content (12.6% and 40.9%, respectively) at salinity stress levels of 4.1 and 8.2 dS/m. The photosynthesis rate of sugarcane leaves decreased by 28.3 to 41.8 percent under salt stress levels of 4.1 and 8.2 dS, respectively. The CP69-1062 variety exhibited a better response compared to the CP73-21 variety, showing relative superiority in all growth and physiological traits studied. Conclusion The results also indicated that the optimal time to apply silicon fertilizer to sugarcane plants was one month before the onset of stress, resulting in a significant improvement in all studied traits. The application of silicon fertilizer led to a 1 percent increase in sucrose, 3.7 percent increase in syrup purity, and 3 percent increase in white sugar yield compared to no application. Acknowledgments We would like to express our special thanks to the Faculty of Agriculture, Shahid Chamran University of Ahvaz for the financial support (Grant number SCU.AA98.336).
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