Research Article
Soil science
Fatemeh Bibi Shahabi; Reza Khorasani; zahra gheshlaghi
Abstract
Introduction:
This study examined the influence of glutathione on iron availability in calcareous soils and its effect on the iron availability from various sources for peanut plants. Calcareous soils, prevalent in many regions, challenge nutrient availability, particularly for micronutrients such as ...
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Introduction:
This study examined the influence of glutathione on iron availability in calcareous soils and its effect on the iron availability from various sources for peanut plants. Calcareous soils, prevalent in many regions, challenge nutrient availability, particularly for micronutrients such as iron, manganese, and zinc, owing to their high pH levels. Despite adequate iron levels in these soils, plant accessibility remains restricted, often resulting in iron deficiency symptoms, such as chlorosis, due to impaired chlorophyll synthesis. Various strategies, including the development of resistant cultivars, organic amendments, and mineral or chelated iron fertilizers, have been explored to mitigate Fe deficiency. Chelated iron fertilizers, especially iron sequestration (EDDHA) agents, are commonly used in calcareous soils to enhance iron availability in plants. However, their environmental impact and cost-effectiveness are concerns, prompting interest in alternatives such as iron oxides, which are cost-effective and environmentally friendly. Research suggests that iron oxides, particularly magnetite nanoparticles, support plant growth and enhance the availability of iron. Additionally, growth stimulants, such as glutathione (a tripeptide with antioxidant properties), have been investigated for their potential to alleviate iron deficiency. Glutathione not only boosts plant defense mechanisms but also improves reactive oxygen species availability. Recent studies have shown that the foliar application of glutathione in iron-deficient plants can significantly increase total iron uptake and enhance photosynthesis. This study aimed to investigate the effects of glutathione on iron bioavailability from various iron sources and growth parameters in peanuts cultivated in calcareous soils.
Materials and Methods (331 words):
The experiment was conducted in a greenhouse at the Agricultural Research Center of Ferdowsi University of Mashha and, employed a completely randomized factorial design with three replications. The factors were iron sources (control, iron sequestration (EDDHA), iron oxide, and iron filings) and glutathione foliar application (0, 1, and 2 mM, four times per growth season: 29, 38, 42, and 48, after planting). Soil was collected from a farm, and some of its physical and chemical properties were analyzed using conventional methods. Macronutrients were added at the recommended dosage to minimise interference with iron treatment. The iron levels were 0 and 50, 1.37, and 0.108 mg/kg for sequestration, iron oxide, and iron filings, respectively. Glutathione foliar treatments were applied at four growth stages (29, 38, 42, 48 days after planting) in concentrations of 0, 1, and 2 mM. The plants were grown in pots with soil moisture maintained at the field capacity. After 66 days, the plants were harvested, and parameters such as dry shoot weight, total iron uptake, and nitrogen were measured. The iron content in plants was determined using atomic absorption spectroscopy, and nitrogen was quantified using the Kjeldahl method. Statistical analyses were conducted using SAS software, and mean comparisons were performed using Duncan's test at the 5% significance level. This study aimed to assess the effects of different iron sources and glutathione on iron bioavailability and plant growth in calcareous soil conditions.
Results and Discussion
The study revealed that glutathione, either alone or in combination with iron sources, notably improved peanut plant growth and iron uptake. Iron sequestration (EDDHA) was the most effective treatment, significantly increasing dry shoot weight, particularly when combined with 2 mM glutathione. The combination of glutathione and iron treatment substantially boosted total iron uptake in both the shoots and roots of peanut plants. Notably, iron sequestration (EDDHA) with glutathione resulted in a 20% increase in shoot iron uptake and a 34.3% increase in shoot nitrogen uptake compared to glutathione treatment alone. Glutathione application also enhanced iron filings, leading to a 55.6% increase in root iron uptake by shoots and a 50.6% increase in iron concentration in shoots, as extracted by phenanthroline. The results indicated that glutathione improves and facilitates iron translocation from the roots to the shoots. Iron filings, a cost-effective iron source, showed significant results when paired with glutathione, enhancing both shoot dry weight and iron uptake. This synergy between glutathione and iron treatments suggests that iron sequestration (EDDHA) is more effective when combined with glutathione, resulting in alleviating deficiency symptoms of iron, such as chlorosis, and promoting overall growth.
Conclusion):
This study underscores the positive impact of glutathione on iron availability and growth in peanut plants grown in calcareous soils. Appliying glutathione significantly increased iron uptake in both shoots and roots, nitrogen uptake, and plant biomass. Iron sequestration (EDDHA), combined with glutathione, emerged as the most effective treatment, improving shoot iron and nitrogen uptake by 20% and 34.3%, respectively. Additionally, glutathione enhanced the efficacy of iron filings, an economical iron source, suggesting its potential as an alternative to expensive iron fertilizers. Glutathione application also reduced chlorosis and improved iron translocation from roots to shoots, supporting its role in enhancing iron nutrition in crops grown in iron-deficient soils. This study offers insights into the role of glutathione in managing iron deficiency stress and recommends further exploration of optimal application rates and effects on diverse crops and soil conditions.
Research Article
Soil science
Mahsa Hasanpour Kashani; Shokrollah Asghari
Abstract
Introduction Soil available water (SAW) is defined as the difference between field capacity (FC) and permanent wilting point (PWP). FC is the amount of soil water content held by the soil after the gravitational water was drained from the soil. PWP is defined as a minimum water content of a soil which ...
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Introduction Soil available water (SAW) is defined as the difference between field capacity (FC) and permanent wilting point (PWP). FC is the amount of soil water content held by the soil after the gravitational water was drained from the soil. PWP is defined as a minimum water content of a soil which is needed for the crop survival and if the water content decreases lower than PWP, a plant wilts and can no longer recover itself. The direct measurement of FC and PWP soil water contents is very costly and time consuming; Therefore, it is useful the use of different intelligent models such as neuro-fuzzy (NF), gene expression programming (GEP) and random forest (RF) to estimate FC, PWP and SAW through easily accessible and low-cost soil characteristics. The objectives of this research were: (1) to obtain NF, GEP and RF models for estimating SAW from the easily accessible soil variables in the cultivated lands of Ardabil plain (2) to compare the accuracy of the mentioned models in estimating SAW using the coefficient of determination (R2), root mean square error (RMSE), mean error (ME) and Nash-Sutcliffe coefficient (NS) criteria.
Materials and methods The measured data from 102 soil samples taken from 0-10 cm soil depth of the cultivated lands of Ardabil plain, northwest of Iran, were used in this study. Sand, clay, mean geometric diameter (dg) and geometric standard deviation (σg) of soil particles, bulk density (BD) and organic carbon (OC) were introduced as input variables to the applied three intelligent models for estimating soil available water (SAW). Data randomly were divided in two series as 82 data for training and 20 data for testing of models. In all models, six different input variables combinations were used; SPSS 22 software with stepwise method was applied to select the input variables. MATLAB, Gene Xpro Tools 4.0 and Weka softwares were used to derive neuro-fuzzy (NF), gene expression programming (GEP) and random forest (RF) models, respectively. One of the important steps using NF method is selecting the appropriate membership functions (MFs) and its numbers. Based on a trial and error procedure, 3 numbers of MFs and 50 to 100 optimum replications were found for the NF modeling. Also, the input MFs were chosen as “triangular”, “trapezoid”, “generalized bell” and “pi” and the output MF was selected as “constant”. A set of optimal parameters were chosen before developing a best GEP model. The number of chromosomes and genes, head size and linking function were selected by the trial and error method, and they are 30, 3, 8, and +, respectively. The rates of genetic operators were chosen according to literature studies. Various tree numbers were analyzed for choosing the best random forest (RF) method. Increasing the tree numbers beyond 100 made lower variations in the average squared error values for the SAW estimation cases. The accuracy of NF, GEP and RF models in estimating SAW was evaluated by coefficient of determination (R2), root mean square error (RMSE), mean error (ME) and Nash-Sutcliffe coefficient (NS) statistics.
Results and discussion The studied soils had loam (n= 53), clay loam (n= 26), sandy loam (n= 15), silt loam (n= 6) and clay (n= 2) textural classes. The values of sand (24.40 to 68.00 %), clay (3.80 to 42.90 %), dg (0.02 to 0.26 mm), σg (7.48 to 19.41), BD (1.04 to 1.70 g cm-3), OC (0.31 to 1.52 %) and SAW (5.10 to 25.10 % g g-1) indicated good variations in the soils of studied region. There were found significant correlations between SAW with BD (r= - 0.59**), clay (r= 0.56**), OC (r= 0.45**) and sand (r= - 0.44**). NF, GEP and RF models were applied to estimate SAW using six different combinations of input soil variables (sand, clay, dg, σg, BD and OC). The results of the best NF, GEP and RF models indicated that the most appropriate input variables to predict SAW were OC and BD. The values of R2, RMSE, ME and NS criteria were obtained equal 0.73, 2.51 % g g-1, 0.09 % g g-1and 0.71, and 0.76, 3.10 % g g-1, - 1.41 % g g-1 and 0.56, 0.68, 3.30 % g g-1, - 1.45 % g g-1, 0.50 for the best NF, GEP and RF models in the testing data set, respectively. Numerous investigations also showed that there are significant negative correlation between SAW with BD and sand and positive correlation between SAW with OC and clay.
Conclusion The results of three investigated intelligent models showed that OC and BD were the most important and readily available soil variables to predict soil available water (SAW) in the studied area. According to the lowest values of RMSE and the highest values of NS, the accuracy of NF models to estimate SAW was more than GEP and RF models. RF approach gave the worst estimates for SAW in this research.
Research Article
Soil science
Fereydun Nourgholipour; maryam mohammady; Hossein Mir Seyed Hosseini; Reza Soleimani
Abstract
Introduction
The cultivation area of canola (Brassica napus L.) has increased globally due to its climatic adaptability and its different growing season compared to other oilseeds. Additionally, its ability to be cropped in rotation with other plants, such as cereals, has contributed to its popularity. ...
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Introduction
The cultivation area of canola (Brassica napus L.) has increased globally due to its climatic adaptability and its different growing season compared to other oilseeds. Additionally, its ability to be cropped in rotation with other plants, such as cereals, has contributed to its popularity. Canola has the largest cultivated area among oilseed crops in Iran. Proper consumption of nutrients is crucial for improving growth and increasing seed yield in canola plants. The use of sulfur as an essential nutrient, along with selenium in low concentrations as a beneficial nutrient, plays a significant role in enhancing plant tolerance to environmental stresses. Sulfur and selenium are both elements of group 16 of the periodic elements table and have similar physical and chemical properties, and it is believed that selenium utilizes the same pathways for sulfur immobilization and uptake in plants. Given the similarity of selenium to sulfur, sulfur metabolic pathways are shared, so the effect of selenium on growth is expected to be largely influenced by sulfur nutrition. This study aims to investigate the effects of sulfur and selenium application on nutrient absorption and their interaction on canola plant growth indices.
Materials and Methods
The experiment was conducted in greenhouse conditions as a factorial in a completely randomized design with 12 treatments and three replications. For cultivation, plastic pots with a diameter of 20 cm were utilized. Four kilograms of sieved soil were added to each pot. 100 mg kg-1 of nitrogen from urea source was applied in the pre-planting stage and 100 mg of nitrogen was applied in two stages (after establishment on day 21 and then in the stem elongation before flowering stage). Triple superphosphate at a rate of 80 mg of phosphorus per kg of soil was added to the pots in powder form before planting and iron at a rate of 5 mg kg-1 in the form of iron chelate solution was added to the pots. The experimental treatments included elemental sulfur fertilizer at two levels of zero and 20 mg kg-1 (inoculated with Thiobacillus inoculum), two sources of selenium fertilizer (sodium selenate and selenite) at three levels of zero, 30, and 60 μg/kg in soil form before planting. The amount of sulfur and selenium available in the soil before planting was 3.8 and 0.025 mg/kg, respectively. The cultivated canola variety was Dalgan and grown in greenhouse conditions for 5 months. This cultivar is open-pollinated. The sulfur was in powder form with a purity of 99%, which was added to the soil of the sulfur-containing treatments, along with Thiobacillus inoculum (with a population of 1×108 cells per ml) two weeks before planting. After the seed growth and maturation period (5 months), at the final stage of growth (physiological maturity with a two-digit growth code of 80), the seed components were separated from the aerial parts. The dry weight of the seed and the aerial parts of the plant were weighed separately.
Results and Discussion
Sulfur application significantly increased shoot dry weight, root dry weight, leaf area, and canola grain weight compared to conditions without sulfur application (48.8% increase in shoot weight, 28.1% in root weight, 15.7% in leaf area, and 51.3% increase in grain weight). Grain weight had a correlation of 0.94** with grain sulfur uptake and 0.9** with shoot sulfur uptake. Therefore, the growth characteristics of roots, shoots, and sulfur concentration in shoots and seeds have a significant impact on grain weight. Application of selenium from selenate source resulted in higher selenium absorption in shoots and canola grain compared to selenite source. In grain, sulfur application increased selenium absorption from both sources. Grain sulfur uptake had a correlation of -0.42** with seed selenium concentration, 0.94** with seed weight, 0.86** with shoot sulfur concentration, -0.43* with shoot selenium concentration, 0.87** with shoot sulfur uptake, 0.7** with shoot weight, 0.69** with leaf area, and 0.83** with root weight. The highest grain selenium concentration was observed at the rate of 60 μg kg-1 from selenate source (0.48 mg kg-1). If increasing the selenium concentration of the grain is desired for enrichment purposes (from 0.12 μg g-1 in the sulfur-free and selenium-free treatments), a sulfur treatment of 20 mg kg-1 and a selenate content of 60 μg kg-1 could be considered to achieve a concentration of 0.42 μg g-1. This is because the grain weight of this treatment (3.87 g pot-1) was closest to the high levels of grain weight in the sulfur treatment of 20 mg kg-1 and selenium-free condition (4.32 g pot-1).
Conclusion
Grain selenium concentrations of 0.10-0.11 mg kg-1 and sulfur concentrations of 0.325-0.33% produced suitable canola yield. The highest canola grain weight was obtained with a concentration of 19.86 mg kg-1 sulfur and 0.0267 mg kg-1 selenium in the soil.
Research Article
Soil science
Yahya Kooch; Mahin Fooladi Doghazlo; Katayoun Haghverdi
Abstract
Abstract
Vegetation, as a key factor in ecosystems, has significant impacts on soil properties through multiple ecological processes. Vegetative covers contribute to soil structure and composition by stabilizing organic matter, controlling erosion, regulating moisture, facilitating nutrient cycling, ...
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Abstract
Vegetation, as a key factor in ecosystems, has significant impacts on soil properties through multiple ecological processes. Vegetative covers contribute to soil structure and composition by stabilizing organic matter, controlling erosion, regulating moisture, facilitating nutrient cycling, and fostering microbial activity. While extensive research has elucidated the effects of various vegetation types on the physical and chemical properties of soil, the biological attributes of soil under different vegetation covers, particularly tree and shrub species, remain underexplored. This study aims to comprehensively evaluate the characteristics of the organic and mineral soil layers in areas dominated by Quercus macranthera tree cover, Crataegus microphylla shrub cover, Berberis integerrima shrub cover, and a mixed Crataegus microphylla and Berberis integerrima shrub cover in Rudbar County, Guilan Province, Iran. By examining these diverse vegetation types, the study seeks to elucidate their differential impacts on soil health and ecosystem functionality, providing insights for sustainable land management.
Materials and Methods
To investigate the influence of vegetation cover on soil properties, a rigorous site selection process was employed. Following preliminary field assessments, study areas were chosen to ensure continuity of vegetation cover and minimal variations in topographic factors, including elevation above sea level, slope gradient, and aspect. This approach minimized confounding variables, allowing for accurate comparisons across vegetation types. In each habitat, two 100 m × 100 m plots were implemented, with a minimum separation of 500 meters to account for spatial variability. Within each one-hectare plot, five soil samples (30 cm × 30 cm surface area, 10 cm depth) were collected from the organic and mineral layers at the four corners and the center of the plot. In total, 10 litter samples and 10 soil samples were collected from each vegetation type and transported to the laboratory for detailed analysis. Laboratory assays evaluated a suite of physical, chemical, and biological parameters, including soil aggregate stability, nutrient content, enzymatic activities, and microbial community dynamics, to provide a comprehensive understanding of soil responses to vegetation cover.
Results and Discussion
The findings revealed marked differences in soil properties across the studied vegetation types. The Q. macranthera tree cover exhibited the highest amount of essential nutrients in the organic layer, including nitrogen, phosphorus, potassium, calcium, and magnesium, reflecting its capacity to enhance nutrient cycling. In contrast, the B. integerrima shrub cover consistently showed the lowest nutrient amounts, suggesting limited contributions to soil fertility. Analysis of physical and chemical soil properties further underscored these disparities. The Q. macranthera cover demonstrated superior soil aggregate stability, higher clay content, increased coarse and fine aggregate percentages, optimal pH, and elevated levels of total nitrogen, ammonium, nitrate, phosphorus, potassium, calcium, and fine root biomass. Enzymatic activities, including urease, acid phosphatase, arylsulfatase, and invertase, were also significantly higher under Q. macranthera, indicating robust microbial and biochemical processes. Conversely, B. integerrima cover recorded the lowest values for these parameters, highlighting its limited impact on soil structure and function. Particulate and dissolved organic nitrogen levels were similarly highest under Q. macranthera, reinforcing its role in organic matter dynamics. Biological soil properties mirrored these trends. The Q. macranthera cover supported the highest densities of soil microfauna, including Acarina, Collembola, and nematodes, as well as abundant protozoa, fungal, and bacterial populations. Metrics of microbial activity, such as basal respiration, substrate-induced respiration, microbial biomass nitrogen, and microbial biomass phosphorus, were also maximized under this tree cover, reflecting a thriving soil microbial community. In contrast, B. integerrima cover exhibited the lowest values for these biological indicators, suggesting a less supportive environment for soil biota. Temporal analysis of carbon mineralization revealed significant variations at weeks 2, 4, 5, 8, and 12, with no notable changes at weeks 1 and 17. The highest carbon mineralization rates were observed under Q. macranthera, while B. integerrima showed the lowest. Nitrogen mineralization followed a similar pattern, with significant changes on days 7, 14, 21, 28, and 35, and the highest rates under Q. macranthera. These results collectively indicate that vegetation type, combined with topographic factors like elevation, significantly shapes the physical, chemical, and biological characteristics of soil in Rudbar County.
Conclusion
This study demonstrates that Q. macranthera tree cover significantly enhances soil quality compared to C. microphylla, B. integerrima, and their mixed shrub covers. The superior physical, chemical, and biological properties observed under Q. macranthera highlight its critical role in fostering soil microbial communities, improving nutrient cycling, and maintaining soil fertility. Enhanced carbon and nitrogen mineralization rates further underscore the importance of this tree species in driving biogeochemical processes essential for ecosystem health. These findings have important implications for land-use planning, forest management, and ecological restoration in Rudbar County. By prioritizing Q. macranthera in reforestation and conservation strategies, land managers can optimize soil productivity and ecosystem resilience. Future research should focus on long-term monitoring of these soil-vegetation interactions and explore additional environmental factors, such as climate and land-use history, to further refine management practices. The integration of such data will support the development of sustainable strategies that balance ecological health with agricultural and forestry objectives, ensuring the long-term vitality of Rudbar County’s ecosystems.
Research Article
Agricultural Meteorology
Fateme Bayatani; Gholam Abbas Fallah Qalheri
Abstract
Introduction
Increasing food security is at the heart of the United Nations’ sustainable development policies. On the other hand, global population growth, the depletion of vital natural resources used in agriculture, and ongoing environmental stresses and climate change undermine the achievement of ...
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Introduction
Increasing food security is at the heart of the United Nations’ sustainable development policies. On the other hand, global population growth, the depletion of vital natural resources used in agriculture, and ongoing environmental stresses and climate change undermine the achievement of this goal. In addition, plant diseases and pests cause 40 percent of agricultural production losses in some major crops on a global scale, seriously jeopardizing food security.
The intensity and frequency of extreme climate events such as heat waves and droughts and climate variability due to climate change will also increase in the future. Potatoes are among the most important agricultural products consumed by humans worldwide. However, potato production is continuously affected by abiotic and biotic factors, the latter of which leads to a loss of 20% of global potato production.
Considering the importance of potato in human diet and its impact on climatic and environmental conditions, especially temperature and humidity, as well as the necessity of studying climate changes in the future, it is necessary to study the conditions of potato cultivation under climate change conditions in the country. Knowing the future climate situation can play a very important role in planning and optimal management of water resources in the continuation of potato cultivation.
Materials and Methods
The study area in this research is the regions of the country that have the highest level of potato production in the country. Considering the climatic diversity in the country, potato crop is cultivated and harvested in two ways: spring and autumn. Therefore, in selecting the stations under study, an attempt has been made to examine both spring and autumn cultivation. The basis for selecting these regions was based on the average percentage of production and cultivated area of each province in the country's potato production during the years 1989-1995.
In order to provide field data for calibration and validation of the WOFOST model under potential conditions, data from research projects of agricultural research centers in Hamadan, Isfahan, Ardabil, Shiraz, Tabriz, Shahrekord, Jiroft, Kahnouj, Manojan, and Sanandaj, which are the main potato production centers of the country, were collected during 2010-2014 and used as the base period.
Daily data of climatic elements including maximum temperature, minimum temperature, precipitation, relative humidity, sunshine hours and average wind speed during the years 1981-2005 related to the studied synoptic stations were obtained from the Iran Meteorological Organization.
The WOFOST model was calibrated for all 10 potato producing stations in the country to predict the duration of the planting to emergence, emergence to flowering, and emergence to physiological maturity stages. After ensuring the high accuracy of the model in the calibration and validation stages, CanESM2 model data were used to assess the consequences of climate change on the growth period and phenological stages of potato in the period 2011-2099 under three radiative forcing scenarios (RCPs). The CanESM2 model data were also refined by the SDSM model. Using the WOFOST growth and development simulation model, simulation of potato phenological stages in the future climate period was carried out using the CanESM2 general circulation model and RCP2.6, RCP4.5, and RCP8.5 scenarios for the study areas.
In order to study and evaluate the effects of climate change on different stages of crop growth and production, future climate conditions must be estimated. Currently, future climate conditions are studied and evaluated using general circulation models (GCM) and different greenhouse gas emission scenarios. Combining the results of climate models with growth and development simulation models allows for the simulation of different phenological stages and crop performance in future climate conditions.
Results and Discussion
The calibration and validation results of the WOFOST model indicated the high accuracy of the model in simulating the phenological stages of the potato plant (sowing to emergence, emergence to flowering, and emergence to physiological maturity), such that the average root mean square error (RMSEn) for all three stages of potato growth in the study areas was below 10%. The results of this study show that the length of the growing season in the study areas will decrease under future climate conditions. The length of the growing season will decrease on average by 4.36 days in the study areas. This decrease was also observed in different growth stages, such that the planting to emergence stage had the least decrease by an average of one day, and the emergence to physiological maturity stage will have the greatest decrease in the length of the growing season.
Research Article
Soil science
Seyed Hamidehi Mousavi Dizkouhi; Mojtaba Barani Motlagh; Esmaeil Dordipour; Elham Malekzadeh; Fardin Sadeghzadeh; mahmmod ghasem nezhad
Abstract
Introduction
The olive tree (Olea europaea L.) is one of the most significant and ancient cultivated plants in the Mediterranean region, prized for its edible fruit and high-quality oil. However, the increasing scale of olive oil production has led to the accumulation of large quantities of solid waste, ...
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Introduction
The olive tree (Olea europaea L.) is one of the most significant and ancient cultivated plants in the Mediterranean region, prized for its edible fruit and high-quality oil. However, the increasing scale of olive oil production has led to the accumulation of large quantities of solid waste, particularly olive solid pomace (OSP), which poses considerable environmental challenges due to its high organic load and phytotoxic components. Sustainable management and valorization of this waste are crucial for reducing environmental risks and improving the circular economy in agricultural systems. This study aimed to evaluate the effects of compost and vermicompost derived from OSP, both in enriched and non-enriched forms, on the yield of olive fruit and the quality characteristics of the resulting olive oil. To this end, a field experiment was conducted during the 2018 growing season in a traditional olive orchard located in Rudbar, Gilan Province, Iran. The experiment was carried out using a randomized complete block design (RCBD) with 12 treatments and three replications on the ‘Arbequina’ cultivar, a well-known olive variety cultivated for its high oil content and quality.
Materials and Methods
Compost and vermicompost were first produced from olive solid pomace. After analyzing their basic physicochemical properties, several treatments were biologically enriched using plant growth-promoting rhizobacteria (PGPR), including Bacillus megaterium (phosphorus-solubilizing), Azotobacter chroococcum (nitrogen-fixing), and Thiobacillus thioparus (sulfur-oxidizing). Additional treatments were chemically enriched by incorporating 1 kg each of urea (as a nitrogen source), triple superphosphate (as a phosphorus source), and elemental sulfur at a rate of 1% by weight. The experimental treatments included: raw olive pomace, unenriched compost, chemically enriched compost, biologically enriched compost, unenriched vermicompost, chemically enriched vermicompost, biologically enriched vermicompost, a full NPK fertilizer treatment, a manure-only treatment (10 kg of animal manure), and a no-fertilizer control. All olive waste-based amendments were applied at 3% w/w. NPK fertilizers included urea (750 g in three split applications), triple superphosphate (250 g), and potassium sulfate (750 g). Micronutrients such as magnesium sulfate, manganese, iron, zinc, copper, boric acid, and elemental sulfur were applied based on soil test recommendations. Uniform horticultural practices, including surface drip irrigation, weed control, pest management, and other cultural operations, were applied across all plots. Post-treatment, soil samples were collected at depths of 0–30, 30–60, and 60–90 cm to measure pH, EC, organic carbon, and available phosphorus. Foliar sprays were prepared with 1,000 ml solutions of urea and potassium sulfate (10 g/L), zinc sulfate (3 g/L), and boric acid (5 g/L) and applied twice at sunset using a handheld sprayer. Fruit yield, oil content, and selected oil quality parameters were then assessed.
Results and Discussion
Application of biologically enriched vermicompost significantly improved olive yield and oil quality. Trees receiving this treatment produced 50.33 kg of fruit per tree—an increase of 93.58% compared to the control. Similarly, the highest oil yield (11.14 kg per tree) was recorded in the biologically enriched vermicompost treatment. The lowest peroxide value (1.06 meq O₂/kg oil) was also observed in this treatment, representing an 88.27% reduction compared to the control. Organic fertilizers positively influenced the oil percentage of the fruit, with biologically enriched compost yielding the highest oil content (57.77%), which was 132.19% higher than the control. The extinction coefficients K270 and K232, indicators of oil oxidation, were reduced by 96.24% and 78.53%, respectively, in the biologically enriched vermicompost treatment. Furthermore, this treatment resulted in the lowest free fatty acid content—94.66% lower than the control. Leaf phosphorus content was also significantly enhanced, reaching 0.33% in the biological vermicompost treatment, a 230% increase over the control. These findings underscore the beneficial role of organic fertilizers, particularly biologically enriched vermicompost, in improving soil fertility, nutrient availability, and plant performance. The high phosphorus content in the compost and vermicompost, combined with microbial activity, played a pivotal role in enhancing both yield and oil quality. The application of PGPRs proved particularly effective, as they not only facilitated nutrient cycling but also contributed to improved physiological responses in olive trees.
Conclusions
Overall, the results suggest that olive trees fertilized with biologically enriched organic amendments derived from olive pomace benefit from improved oil quality and fruit yield. The presence of adequate phosphorus and beneficial bacteria played a pivotal role in enhancing plant nutrition and oil characteristics. Therefore, the use of PGPR in the enrichment of composted organic materials can be an effective and sustainable strategy to improve the productivity and quality of olive oil. Among the treatments, biologically enriched vermicompost emerged as the most effective and is recommended for further field application. Future research should explore other organic amendments and their long-term effects on olive orchards.
