مجله تغذیه گیاهان باغی
سال چهارم شماره 2 (پیاپی 8، پاییز و زمستان 1400)

The word biostimulant was apparently coined by horticulture specialists for describing substances promoting plant growth without being nutrients, soil improvers, or pesticides. The use of fresh seaweeds as a source of organic matter and as fertilizer is ancient in agriculture, but biostimulant effects have been recorded only recently. Chemical elements that promote plant growth and may be essential to particular taxa but are not required by all plants are called beneficial elements. The two main beneficial elements are Se and Si, present in soils and plants. Many effects of beneficial elements are reported by the scientific literature, which promotes plant growth, the quality of plant products, and tolerance to abiotic stress. This includes cell wall rigidification, osmoregulation, and reduced transpiration by crystal deposits, thermal regulation via radiation reflection, enzyme activity by co-factors, plant nutrition via interactions with other elements during uptake and mobility, antioxidant protection, interactions with symbionts, pathogen and herbivore response, protection against heavy metals toxicity, plant hormone synthesis and signaling. This study aimed to investigate the effect of different culture media and foliar application of some biostimulants (silicon, selenium, and seaweed extract) on growth characteristics and yield of tomato (cv. Dafnis) under hydroponic condition.

This study was a factorial experiment based on a completely randomized design with two factors of culture media (50% cocopeat + 50% perlite and 50% palm peat + 50% perlite) and foliar fertilizer application (control, concentration of 10 and 20% of seaweed extract, 25 and 75 mg/L sodium silicate and 4 and 10 mg/L sodium selenite) were applied in four replications.

This experiment showed that each of the main factors significantly affected the growth characteristics except stem diameter, number of leaves, and leaf area. There was no significant difference in terms of yield and yield components between palm peat + perlite with cocopeat + perlite. It was also found that foliar application of seaweed extract, silicon, and selenium significantly improved yield and yield components compared to the control treatment. So that among the studied treatments, the highest increase in yield was obtained with the application of 20 % concentration of seaweed extract as well as 75 mg/L sodium silicate.

In general, palm peat in combination with perlite can be used as a suitable media in hydroponic cultures. Also, foliar application of seaweed (20 %), silicon (75 mg/L), and selenium (10 mg/L) had positive and significant effects on vegetative growth and yield of tomato and can be recommended in commercial tomato greenhouses.

In order to improve the quantity and quality of medicinal plants, the use of natural substances such as amino acids have increased in recent years, which provide little information on their individual effects, as well as interaction with other fertilizer sources.

To investigate effect of different fertilizers and the foliar application of L-phenylalanine on nutritional elements of hyssop [Hyssopus officinalis L. subsp. angustifolius (Bieb.)], an experiment was done in a randomized complete block design with three replications during two consecutive years of 2016 and 2017 in a field experiment at the experimental field, Shahrekord. The investigated factors were fertilizer treatments including chemical fertilizer (NPK), organic fertilizers (animal and vermicompost) and a bio-fertilizer, mycorrhizal fungus (including Glomus genus) in the main plots and L-phenylalanine (at three levels: 0, 500, and 1000 mg/L) in sub plots.

Results indicated that the application of different fertilizers along L-phenylalanine at two studied concentrations (500 and 1000 mg/L) led to significant increase in the concentration of most nutrient elements including nitrogen (N), phosphorus (P), potassium (K) and micro elemts [Iron (Fe), zinc (Zn), manganese (Mn) and copper (Cu)] in the leaf were compared to the control. Among them, the application of fungal and vermicompost fertilizers, L-phenylalanine × fungal fertilization, and phenylalanine × vermicompost had highest effects on the increase of these traits. In conclusion, the results indicated that the application of organic fertilizers along with L-phenylalanine spraying at 1000 mg/L level has a beneficial role in the improvement of nutritional elements and dry matter yield of H. officinalis L. subsp. angustifolius (Bieb.).

One of the strategies for improving citrus yield and fruit tolerance to frost in citrus gardens is practicing balanced fertilization. So that if the concentration of each element is lower than the optimum concentration, the yield of the plant will be reduced. Therefore, the aim of this study was to investigate the role of optimum fertilizer application on increasing quantitative and qualitative yield of oranges and also resistance to cold stress.

In order to investigate the role of balanced fertilization on some of the characteristics of citrus fruits, including increased resistance to frost, a two-year trial was conducted on Thomson and Bloody Thomson with two treatments and five repetition in the years of 2016-17 and 2017-18 in a citrus garden in Neka city in Mazandaran province. treatments included, T1= control (Traditional fertilization method, i.e. every year in late autumn, 2 kg of urea, 1 kg of triple superphosphate per tree, along with animal manure under droppers) and T2= balanced fertilization according to the soil and leaf analysis results, i.e. every year in late autumn, 2 kg ammonium sulfate, 1.5 kg potassium sulfate 1 kg magnesium sulfate and 0.5 kg zinc sulfate mixed with animal manure and surface soil with deep placement under droppers. It should be noted that in both years, the same fertilizer sources were used. Also, in the summer of second year, for each tree, 0.5 kg of soluble potassium sulfate with zinc (SSOP+Zn-EDTA) was used in two split times (July and August).

The results revealed that a) In the first year, while the average yield in T1 for Thompson Blood Orange and Thompson Novell Orange were 40 and 75 kg, in T2, it increased up to 72 and 175 kg per tree and in the second year, also these figures were increased significantly from 80 and 140 kg and 155 and 305 kg per tree, respectively. In both years, the differences were significant at 1% level. The main reason for this performance in the second year was due to split application of SSOP+Zn during the summer. b) While the average dry matter percentage for Thompson Blood Orange and Thompson Novell Orange for the first year in T1 were 15.6 and 22%, in T2 they were increased to 17.1 and 24.4%, respectively. For the second year, they were increased from 18.1 and 22.3% in T1 to 20 and 25.2% in T2, respectively .c) While frost tolerance in Thompson Blood Orange and Thompson Novell Orange during the first year in were 0 and -1 degrees Celsius in T1, frost tolerance were increased in T2 up to -2 and -5 degrees Celsius. In the second year, these figures were changed from -1 and -3 to -4 and -9, respectively. One of the main reasons for this improvement in frost tolerance of citrus fruits was due to increase in their dry matter percentage and positive effects split application of K and Zn fertilizers.

While the superiority of balanced fertilization has been proven, it is highly recommended that for producing valuable citrus fruits, this practice should be generalized in all citrus gardens.

Balanced fertilization of organic matters and macro- and micro-nutrients is the most important effective factors on the fruit quality and the yield of the citrus trees (Hao et al., 2007). A very large area of land under cultivation in the south of the Iran is calcareous, and as a result, the absorption of elements such as zinc, phosphorus, iron, etc. in these soils is done slowly, which is one of the agricultural problems of these areas (Aboutalebi and Hassanzadeh, 2007). In the subtropical regions, flowering in citrus occurs after the infancy period and exposure to low temperatures and short days of winter (Nebauer et al., 2006). This study was conducted with the aim of investigating the effect of nitrogen and zinc on increasing the fruit quantity and quality of the 6-old-years sweet lime.

This investigation was performed as factorial arrangement in randomized complete block design with nine treatments and three replications and one 6-years-old sweet lime tree budded on the Mexican lime rootstock in each replication in two separate parts of the big research orchard of Islamic Azad University of Jahrom branch. The experiment factors included the foliar application of urea at three concentrations of 0, 3 and 5 gL-1 and the foliar application of zinc sulfate at three concentrations of 0, 3 and 5 gL-1. The foliar application of urea and zinc sulfate was performed before flower induction of the trees, in October. After spraying, in the time of the fruit harvesting, the parameters including fruit juice pH, TSS, vitamin C, average fruit weight, texture firmness, single tree yield and fruit ripening were measured.

Based on the results, in the present study due to foliar application of urea and zinc sulfate particularly combined treatments, all traits significantly influenced compared to control treatment. Totally, the treatments without urea were in the lowest levels in viewpoint of quantitative and qualitative characteristics of the fruit. The use of 5 gL-1 zinc sulfate without urea and/or 3 gL-1 urea without zinc sulfate as well as combined treatment of 3 gL-1 urea and 5 gL-1 zinc sulfate caused to improve qualitative characteristics of the fruit. The use of 5 gL-1 zinc sulfate without urea led to increase the peel thickness and fruit firmness. Combined treatment of 5 gL-1 urea and 5 gL-1 zinc sulfate increased average fruit weight and plant yield.

In the present study, the foliar application of urea and zinc sulfate, particularly in the combined treatment, significantly affects all parameters compared to control treatment. On this basis, it can be recommended the foliar application of 5 gL-1 urea + 3 gL-1 zinc sulfate in the October to improve qualitative traits of the fruit and the combined treatment of 5 gL-1 urea + 5 gL-1 zinc sulfate to increase the yield of sweet lime.

In a two-year field experiment, the effects of combined application of manure and trace elements of iron, zinc and boron on the quantitative and qualitative characteristics of cantaloupe cultivar Semsouri in a calcareous soil was studied. Application of manure and trace elements increased yield, yield components and TSS (Total soluble solids). The highest cantaloupe yield(43.9 tons per hectare) and the highest average number of fruits per cantaloupe plant (4.45) were obtained from the application of 40 tons per hectare of manure and foliar application of iron, zinc and boron that increased 36 and 41% compared to the control treatment, respectively. Also, the percentage of TSS increased with the application of manure and foliar application of microelements, especially boron. The highest TSS (sugar) of cantaloupe was obtained at 9% from the application of 40 tons per hectare of manure and foliar application of iron, zinc and boron, which was 49% more than the control treatment. Data indicated that there was a significant correlation between the percentage of soluble solids in fruit and the concentration of cantaloupe leaf boron that the equation of this regression model followed the linear model.

Iran is one of the important countries of the world for growing flowers and ornamental plants. One of the reasons for such high capability is due to different climates in this area. Lilium from Liliaceae family is one of the most important bulbous cut flowers, which maintaining its postharvest quality has a special importance . Nutrition is one of the factors affecting the preservation of cut flowers quality.

In this study, effects of the ordinary super phosphate (0, 50, 100 and 150 mg l-1) and mycorrhizal fungi in two levels of consumption and non-consumption (0 and 50 mg per 5 kg soil) were investigated according to a factorial experiment, using a completely randomized design with 4 replications to study the morphological and physiological traits of Lilium Longiflorum cultivar ‘Royal Trinity’. Different parameters as; stem height, bud diameter, leaf length (in two areas), bulb weight, postharvest longevity, amount of soluble sugar, Non-soluble sugar, phosphorus and potassium were measured.

Results indicated that applying different levels of phosphate and mycorrhizal fungi significantly increased stem height, bud diameter, leaf length (in two areas), bulb weight, postharvest longevity, amount of soluble sugar, Non-soluble sugar, phosphorus and potassium, in compare with control. Mycorrhizal fungus, due to the extensive networks and increase the area and rate of root absorption, increases the efficiency of plants in absorbing water and nutrients, especially phosphorous elements and finally improve their growth (Vosatka and Albrechtova, 2009). Phosphorus content also affects physiological parameters in plants. One of the parameters is increase in the amount of photosynthesis. It has been shown that phosphorus plays an important role in transfering energy during photosynthesis. Therefore, mycorrhiza fungus is a stimulant to enhance photosynthesis (Demir, 2004).

Mycorrhizal fungi have beneficial effects on plant symbiosis. The beneficial effects of mycorrhizal fungi are on improving the nutritional status of host plants, especially phosphorus.

Nitrogen is essential for plant growth. Excessive use of nitrogen fertilizers causes nitrate uptake and accumulation in edible parts of plants. This study was conducted to evaluate the nitrate concentration in some vegetables collected from the Kermanshah vegetable market in winter 2020.

vegetable samples include leafy, fruit-bearing, and tuberous vegetables were collected from the main vegetable market in Kermanshah city four times. Leafy samples were cress, lettuce, spinach, and celery. Fruit-bearing samples included cucumber and tomato. Tuberous samples included red and yellow onions and potatoes. The sampling times were January, early and mid-February, and March. Our previous study showed that vegetables in the main vegetable market of Kermanshah have been provided by different cities of Iran. Therefore, if there was one vegetable type has been supplied from different locations or different cultivation methods (i.e. traditionally vs. in greenhouse conditions), individual samples were collected. The nitrate concentration of vegetable samples was determined by the colorimetric method (Cataldo et al., 1975) after their preparation and extraction (Jones, 2001). The results were analyzed via SPSS v.26 by one-way ANOVA after testing the normal distribution. The means were compared by Duncan’s test (P<0.05). However, to determine the health status of vegetables, their concentrations were compared with the nitrate limit defined by the World Health Organization (WHO) (WHO, 1978) and the Institute of Standards and Industrial Research of Iran (ISIRI) (ISIIR, 2013). The differences in nitrate concentration of crops were also compared according to the time of sampling, the place (i.e. city that crops were grown), and the cultivation methods.

The results showed that nitrate concentration in lettuce, celery, cucumber, tomato, yellow onion, and potato was significantly lower than the ISIRI nitrate limit (P<0.001). Also, the nitrate concentration in cress samples in last February and March, spinach samples in mid-and las-February, and red onion samples in January and mid-February were lower than the permissible nitrate limit. However, nitrate concentration in cress and red onion (in January and mid-February) and spinach (in January and March) was higher than the WHO and ISIRI nitrate limit. ANOVA results revealed significant differences in vegetable nitrate concentration between months (P<0.001). The results also indicated that the variances of nitrate concentration in cress, cucumber, and tomato samples were highly influenced by place (P<.01). Moreover, nitrate concentration in the above-mentioned samples traditionally cultivated was found to be not significantly different from those grown in the greenhouse.

The results of this study showed that the time of sampling and the place where vegetables are grown affects the variation of nitrate concentration. However, the cultivation method showed no significant impact. However, the number of samples in this study was less than the amount to conclude this result certainly. Therefore, it is recommended that the nitrate concentration of the vegetables be measured at different sampling times as well as for vegetables grown in different places with more samples to assess the status of nitrate more confidently. This would help to have a reasonable allowable nitrate concentration limit for vegetables in comparison with the WHO standard.

Salinity is a significant restriction for the cultivation of horticultural crops. Pear trees are generally classified as salt-sensitive. Nitric oxide (NO) is an endogenous signaling molecule that plays a crucial role in various physiological processes, including salinity stress. Variations in endogenous NO levels and or exogenous NO application has shown to regulate abiotic stress resistance suggesting that this approach may contribute in enhancing crop production under stress conditions. In this research, the effects of NO treatment on some parameters NaCl stress tolerance were investigated in Pyrodwarf and OHF69 pear (Pyrus communis) rootstocks in order to evaluate the tolerance of Pyrodwarf and OHF69 pear rootstocks under NaCl stress.

The experiment was conducted in the research greenhouse of University of Tabriz in 2018. The experiment was factorial based on a completely randomized design with three replications. Sodium nitroprusside as a NO donor (0, 0.1, 0.5 and 1 mM) was applied to pear rootstocks under NaCl stress (0, 50, 100 and 150 mM) through the root system. NO treatments were applied at four levels along with nutrient solution through the root with the interval of 2 weeks. At the end of the experiment, the parameters of the height increment, relative water content (RWC), malondialdehyde content, proline, H2O2 and the concentration of Na+ and K+ of the leaves were evaluated. Data analysis was done using SPSS, version 22, and mean comparison was performed using the Duncan test at a 5% level.

The NO application significantly increased height of pear rootstocks, RWC and proline of leaves, and decreased malondialdehyde, H2O2 content of leaves both OHF69 and Pyrodwarf rootstocks exposed to NaCl stress. These results are in agreement with previous studies in citrus (Tanou et al., 2012) and apple (Aras et al., 2020). NO-treated plants showed a higher amount in both K+ concentration and K+/Na+ ratio and lower Na+ concentration. It is important to maintain the balance of nutrients in plant growth under salinity, and SNP treatment reduced the concentration of Na+ in plants exposed to salinity stress in citrus (Khoshbakht et al., 2018) and strawberry (Kaya et al., 2019). OHF69 rootstocks had higher amounts in relative water content, proline and K+/Na+ ratio than pyrodwarf rootstocks, and also showed lower content of H2O2 and Na+ concentration. The results of this experiment indicate that 1mM NO application mitigated the damages of NaCl stress. Moreover, OHF69 rootstocks at all salinity levels of NaCl indicated a higher relative tolerance compared to Pyrodwarf.

According to the results, NO application mitigated the negative effects of NaCl stress. Also, it is considerable that treated plants with 1 mM SNP under 50 mM NaCl stress had no significant difference compared to the control plants, which can be considered to stress tolerance under short-term salinity condition, and OHF69 rootstocks at all salinity levels of NaCl showed a higher relative tolerance compared to Pyrodwarf.Keywords: H2O2, proline, Pyrus communis, sodium nitroprusside, stress

Introduction:

 Titanium dioxide nanoparticles (TiO2NPs) generally have positive impacts on the growth, biochemical, and physiological characteristics of plants. Salinity is one of the major environmental factors that limited the growth and production of most crops due to the different plant species and growth stages. Based on severity and duration of the salinity stress different reactions of the plants were observed. Salinity reduces the growth of plants due to the existing osmotic materials around the roots. In addition, salinity exerts hypertonic stress on the plants. Under salinity, ions, mostly Na+ and Cl-, accumulate in the tissues of plants and cause significant physiological disorders and reduction in plant growth and development. Therefore, using different methods for reducing the harmful effects of salinity is very important. Various ameliorating agents such as nanoparticles (NPs) have been used for combating various abiotic stresses like salinity. Application of NPs to stressed plants have been shown to mitigate stress-induced oxidative and osmotic stress. Calendula officinalis L. (marigold) is an annual ornamental and medicinal plant from Asteraceae family that widely cultivated for different purposes like producing industrial products in culinary, pharmaceutical, and cosmetics industries.

Materials and Methods:

 This study aimed to evaluate the effects of TiO2NPs on biochemical and physiological parameters of marigold (Calendula officinalis L.) under NaCl stress. Treatments included TiO2NPs applied as foliar spraying in three levels (50, 100, and 200 mg/L), no foliar application as control, and different NaCl levels (0, 30, 60, and 90 mM) by adding NaCl into irrigation water.The studied traits were included growth characteristic (height, number of brunches, Number of flowering branch Number of flowers, Flower diameter, Total flower fresh weight, Total flower dry weight, Flower yield, Leaf area , Plant fresh and dry weight, Root fresh and dry weight, Root length and volume)) and element content (N, P, K, Fe, Mn,Mg,Ca, Zn, Na, Ti). Statistical analysis was performed using JAMP 13software. The mean comparison was done by LSD test at the 5% probability level.

Results and Discussion:

 The results of the mean comparison showed that, with increasing salinity, the growth characteristics of the plant decreased and the application of titanium dioxide nanoparticles, especially in 200 mg/L level, improved these traits. In addition salinity affected the nutrient uptake of the plant. Application of titanium dioxide nanoparticles improved the nutrient uptake of marigold under NaCl stress. According to the findings of this study, titanium dioxide nanoparticles mitigate the detrimental effects of salinity on the studied traits which were decreased under different NaCl concentrations.Among different titanium dioxide nanoparticles levels that used in this study, 200 mg/L is more effective than the other concentrations.

Conclusions:

 Based on the results of this experiment, the stimulatory effect of foliar application of TiO2NPs under NaCl stress on enhancing growth characteristics and nutrient uptake of marigold were observed in this study. At the higher NaCl levels, the negative effects of NaCl on plant growth and osmotic abilities were observed. The application of titanium dioxide nanoparticles had different effects on the studied traits. TiO2NPs application increased the studied parameters under salinity stress in comparison with no application of TiO2. In most cases, 200 mg/L titanium dioxide was the most effective concentration to mitigate the negative effects of salinity.In addition, TiO2 helped the plants to resist NaCl stress and mitigate the harmful effects of salinity.On the other hand, proper osmoprotectants and antioxidants may induce the synthesis and accumulation of bioactive naturally compounds. Based on the findings of this study, it is concluded that foliar application of TiO2NPs under NaCl stress can alleviate the deleterious effects of salinity and also improve the growth of marigold by increasing the nutrient element content such as Fe, Mg and N that effective in chlorophyll synthesis.

Leafy vegetables are widely consumed in many countries due to their high nutritional value. However, leafy vegetables are the primary source of nitrate accumulation, and therefore, daily consumption of nitrate-containing vegetables can cause many problems for human health. Spinach (Spinacia oleraceae L.) is one of the leafy vegetables that accumulate nitrate. Many nutrients are involved in reducing nitrate accumulation and metabolic and physiological processes in plants. Among the elements, selenium, which is known as a beneficial element, at low concentrations, it can have beneficial effects on plant metabolism as well as reducing nitrate accumulation.

This study was conducted to investigate the effect of selenium and selenium green nanoparticles on nitrate accumulation in spinach in a randomized complete block design with seven treatments and seven replications. Treatments included sodium selenite (Na2SeO3) at concentrations of 1, 2, and 4 mg l-1 and green nanoparticles of sodium selenite (Se NPs) at concentrations of 1, 2, and 4 mg l-1 and control (without the use of selenium), which used as foliar sprays.

The results showed that most of the nutrient treatments, especially the concentration of 4 mg l-1 sodium selenite and 1 mg l-1 Se NPs, significantly increased the fresh and dry weight of the plant, chlorophyll a, chlorophyll b, total chlorophyll, and the activity of nitrate reductase and decreased the concentration of nitrate. In most of the nutrient treatments, the levels of phosphorus, potassium, and selenium were higher than the control. In contrast, the control plants showed significantly more Zn than the plants treated with different selenium levels.

As demonstrated by the results of current research, foliar application of Se, especially Se NPs, have a high potential for obtaining better quantity and reducing the nitrate accumulation in spinach.

Kiwifruit (Actinidia chinensis) is an important subtropical fruit appreciated by consumers due to its excellent qualitative attributes and its nutritional properties, especially high ascorbic acid content, which provide health benefits. A balanced fertilization of macro- and micro-nutrients for plant nutrition is essential for enhancing fruit yield and quality (Ashouri Vajari et al., 2018). Foliar application is a complementary method for plant nutrition and is mostly used in cases where the plant urgently needs a certain element and also in early spring when the absorption of elements from the soil is low due to low root activity. Also, in cases where the soil conditions are not suitable for the absorption of elements, it is a relatively easy method and it yields quickly. Nitrogen, boron and zinc have the greatest effect on pollination, fertilization and fruit formation. In early spring, due to the cold soil temperature and the lack of sufficient leaves on the plant, the absorption of these elements from the soil is less and therefore it is necessary to provide these elements to the plant by foliar application. However, there is little information concerning the effect of nitrogen, boron and zinc application on golden kiwifruit. Thus, this research was carried out to determine the effects of preharvest urea, boric acid and zinc sulfate application on quality and some mineral nutrients concentration in golden kiwifruit.

The experiment was conducted in a randomized complete block design with three replications in Astara. Experimental treatments include: control (spraying with water), urea with a concentration of 1.5%, zinc sulfate (2000 mg L-1), boric acid (1500 mg L-1), urea 1.5% + zinc sulfate (2000 mg L-1) 1.5% urea + boric acid (1500 mg L-1 the composition of urea was 1.5% + zinc sulfate (2000 mg L-1) which in three stages of plant development including the beginning of bud swelling (early March), the beginning of sepal splitting (Late April) and the rapid fruit growth stage (early June) were sprayed. Fruit were harvested at commercial maturity in the morning and transported in an air-conditioned vehicle to to the fruit analysis laboratory at Zanjan University, and subjected to physicochemical analysis.

The results showed that foliar application of the mentioned compounds had a significant effect on the amount of total soluble solids, fruit dry weight, fruit firmness, ratio of soluble solids to total acid, ascorbic acid, total phenols, flavonoids and antioxidant capacity of fruit. All studied traits except soluble solids and the ratio of solids to total acid increased due to foliar application of nutrients. Foliar application of urea, boric acid and zinc sulfate alone or in combination increased these elements in leaves and fruits. The best treatment was for combined foliar application of 1.5% urea + sulfate on 2000 mg L-1 + boric acid 1500 mg L-1 that all the traits measured in this treatment had the highest. According to the obtained results, it can be stated that the simultaneous use of urea, boric acid and zinc sulfate increases the quality and antioxidant capacity of golden kiwifruit.

Conclusively, combined foliar application of urea (1.5%) plus zinc sulfate (2000 mg L-1) and boric acid (1500 mg L-1) at three stage can be used effectively to improve leaf nutrient status and nutritional quality of golden kiwifruit.

Drought stress is one of the non-living environmental stresses that affect the quantity and quality of plant yield (Eyni-Nargeseh et al., 2020), and it is the most important factor in reducing yield and crop production in plants (Xu et al., 2020). Elements such as potassium play an important role in controlling water loss from the plant (Farahani et al. 2019). Potassium is an essential nutrient and is one of the most abundant cations in plants, which plays an important role in plant growth and in almost all related functions (Zahoor et al., 2017). Summer Savory (Satureja hortensis L.) is one of the most widely used medicinal plants. It is an herbaceous or perennial plant and a member of the aromatic plants of the family Mint (Lamiaceae), which has a rodent flower, the flowers appear in the axils of the upper leaves, the flowers are male and female and are seen in white to purple colors (Yazdanpanah et al., 2011). Finding solutions to reduce the effects of drought stress and improve plant growth and yield is essential. Therefore, the aim of this study was to investigate the effect of the application of different levels of potassium sulfate on increasing yield, biochemical properties, and drought resistance in Summer Savory.

This research was carried out as a factorial split-plot based on a randomized complete block design with three replications at the research farm of Ferdowsi University in 2015-2016. The main factors included drought stress at three levels (50, 70, and 100% of field capacity) and potassium sulfate fertilizer at four levels (0, 100, 200, and 300 kg/ha) and the sub-factor of two harvest times. All traits were measured at the flowering stage. The studied traits included growth characteristics (using conventional methods), photosynthetic pigments (Lutts et al., 1996), soluble carbohydrates (Paquin et al., 1979), antioxidant activity (Moon et al., 1998), and total phenol (Singleton et al., 1965). Minitab17 software was used to analyze the data. The mean comparison was performed based on the Bonferroni test.

The results showed that with increasing drought stress, the amounts of chlorophyll a, b, total, soluble carbohydrate, antioxidant activity, and total phenol increased. However, with increasing drought stress, growth characteristics and carotenoids decreased. So that with increasing drought stress, the amount of plant height at the highest drought stress level (50% of field capacity) decreased by 33.99% compared to the control. Based on the results of this study, the application of potassium sulfate fertilizer under drought stress conditions reduced the effect of drought stress, as the highest amount of growth characteristics and photosynthetic pigments were observed in the application of potassium sulfate fertilizer. At the highest level of drought stress and application of 300 kg/ha of potassium sulfate in the first harvest time increased plant height, chlorophyll a, b, and total by 62.14, 82.36, 93.09, and 87.35%, respectively, but decreased antioxidant activity (13.86%) and total phenol content (34.38%).

Based on the findings of this study, the use of potassium sulfate fertilizer reduces destructive effects under environmental stresses, including drought stress. In particular, the application of 300 kg/ha of potassium sulfate fertilizer had the best results in drought stress conditions in Summer Savory which can be used as a management solution in drought-prone areas.