Application Of K2SO4 Research Articles

Foliar Spraying of Potassium Sulfate during Fruit Development Comprehensively Improves the Quality of Citrus Fruits

Sugar accumulation is influenced by various fertilizer treatments, of which potassium spraying is the most effective. However, the effect of different potassium sources as a foliar application at different fruit development stages on citrus fruits is still unclear. In this study, three different potassium fertilizers and one water (F1: 0.65% KNO3, F2: 0.88% KH2PO4, F3: 0.56% K2SO4, and F4: water) were sprayed on Citrus reticulata cv. Nanfeng at cell division, cell expansion, fruit ripening, and throughout fruit developmental stages, respectively. Results showed that the six-time K2SO4 application had the best function in enhancing fruit physiological attributes such as fruit weight and the total carotenoids; also, this treatment significantly decreased TA (titratable acid), increased fruit TSS (total soluble solids), soluble sugar content, and TSS:TA ratio. Furthermore, K2SO4 spraying obviously increased the expression of CsCWINV-2/6 in the segment membrane, and CsSUT-1/2 and CsVPP-1/2 in fruit juices. Taken together, six-time application of K2SO4 throughout fruit developmental stages produced better fruit quality, at least through enhancing sink strength and promoting sugar transportation in citrus fruits. This study might effectively contribute to maximizing fruit quality and its marketability.

Potassium Nutrition Induced Salinity Mitigation in Mungbean [Vigna radiata (L.) Wilczek] by Altering Biomass and Physio-Biochemical Processes

The present investigation was conducted to explore the role of potassium nutrition in improving biomass and physio-chemical alterations to reduce the adverse effects of salinity in mungbean. A sand-culture experiment was carried out under different salinity levels (0, 50, and 100 mM NaCl) with two levels of potassium (0 and 50 mM K2SO4) and two mungbean cultivars (NM-92 and Ramzan), and the alterations in mungbean biomass and metabolic activities were investigated. The results suggested that salinity significantly reduced the biomass, nitrate reductase activity (NRA), nitrite reductase activity (NiRA), total soluble proteins, chlorophyll a, chlorophyll b, total chlorophyll, nitrogen, potassium, calcium, magnesium, and phosphorous contents in both mungbean cultivars in comparison to the control. However, K2SO4 at 50 mM significantly improved all the parameters in both mungbean cultivars except for the sodium content. A significant increase in the total free amino acids, carotenoids, and sodium content in both mungbean cultivars was observed due to salt stress. Moreover, principal component analysis and heatmaps were developed individually for both mungbean cultivars to assess the variability and correlation among the studied attributes under all applied treatments. Under saline conditions, the mungbean ‘Ramzan’ showed more marked reductions in almost all the growth parameters as compared to ‘NM-92’. The results suggest that the application of K2SO4 ameliorates the adverse effects of salinity by regulating osmolyte production, NRA, and NiRA, thus promoting plant growth and productivity.

Foliar applications improves grapevine plant cold hardiness

Understanding and enhancing the cold hardiness of vines is crucial for viticulture, as it directly impacts the sustainability and productivity of vineyards in diverse climatic regions. This study, therefore, meticulously examined grapevine responses to various treatments and sampling times, revealing nuanced dynamics in cold tolerance, physiological parameters, and growth outcomes. Our study found that treatments like K2SO4 significantly enhanced grapevine cold hardiness. Specifically, K2SO4 showed high R² values, indicating a substantial improvement in low-temperature hardiness for primary buds and in processes like bud burst and sprouting. Our results also revealed significant differences in cold hardiness across various treatments and sampling times, with K2SO4 leading to the highest LT50 value for primary buds. Additionally, in single-bud cuttings, K2SO4 application improved viability rates, root and shoot growth, and rooting rates, particularly observed in January. Growth parameters in single-bud cuttings further illustrated the impact of treatments, with the viability rate of primary buds being 61.5 % in the K2SO4 application and 62.0 % in the CaCl2 application. The highest root length of 2.5 cm and shoot length of 3.4 cm, along with a rooting rate of 61.0 %, root scale of 1.4, root number of 6.9, and basal callus rate of 24.6 % were obtained from the K2SO4 application. Our research found that the applications of K2SO4 and CaCl2 increased the cold hardiness of the buds and phloem tissue of the vine by approximately 1 °C compared to the control. It has been concluded that K2SO4 and CaCl2 applications during development can reduce the cold injury rate and economic losses in vines in areas with high risk of winter cold damaging events. The comprehensive findings of this study offer actionable insights that can significantly contribute to the refinement of vineyard management practices, promoting optimal grapevine performance and hardiness in the face of varying cold conditions.

Influence of Fertigation and Granular Applications of Potassium Fertilizer on Soil pH and Availability of Potassium and Other Nutrients in a Mature Planting of Northern Highbush Blueberry

Although northern highbush blueberry (Vaccinium corymbosum L.) fields are often fertigated using soluble or liquid fertilizers, recommendations for applying most nutrients to the crop, including K, are based on the use of granular fertilizers. The objective of the present study was to compare fertigation to granular application of K in a mature planting of Duke, a popular early season blueberry cultivar that ripens from June through July in Oregon and Washington. The plants were grown on raised beds and irrigated using two lines of drip tubing per row. Treatments were initiated in 2016 and included no K fertilizer, a single application of granular potassium sulfate (K2SO4) in April, and fertigation once a week from April to August with soluble K2SO4 or liquid potassium thiosulfate (K2S2O3). Each treatment was applied for 2 years at a total rate of 70 kg·ha−1 K per year. The plants were also fertigated with 168 and 224 kg·ha−1 N in 2016 and 2017, respectively, and 30 kg·ha−1 P per year. Although extractable soil K was initially low at the site (144 mg·kg−1), the treatments had no effect on plant dry weight, yield, fruit quality, or the concentration of K in recently expanded leaves. However, during the first year of the study, K fertigation with K2SO4 or K2S2O3 reduced soil pH and increased the concentrations of K+, Ca2+, Mn2+, and SO42− in the soil solution under the drip emitters compared with no K or granular K2SO4, whereas granular application of K2SO4 resulted in higher concentrations of K+ between the emitters than any other treatment. Fertigation also affected the concentration of K in the fruit during the first year, although in this case, the concentration was lower with K fertigation than with no K or granular applications of K2SO4. During the second year, fertigation and granular K continued to result in higher concentrations of K+ in soil solution under and between the drip emitters, respectively, but at this point, extractable soil K was higher with each of the K fertilizers than with no K. Consequently, the concentration of K in leaves sampled from entire plants in late September that year was higher with any of the K fertilizers than with no K. Potassium fertilization also altered concentrations of other nutrients in the plants, including Mg, S, B, Cu, and Mn in the leaves; Ca, Mg, and B in the fruit; Mn and Zn in the woody canes; and P, Mg, S, and Mn in the crown. In many cases, concentrations of these nutrients were higher with one or more of the K fertilizers than with no K. Thus, regardless of the application method, K2SO4 and K2S2O3 appear to be good sources for increasing availability of K and other nutrients in the plants and soil. However, the amount of K in the plants was sufficient at the site, and therefore, none of the fertilizers provided a short-term benefit to growth or fruit production in the present study.

Long-term excessive application of K2SO4 fertilizer alters bacterial community and functional pathway of tobacco-planting soil.

To improve tobacco leaf quality, excessive K2SO4 fertilizers were applied to soils in major tobacco-planting areas in China. However, the effects of K2SO4 application on soil microbial community and functions are still unclear. An eight-year field experiment with three kinds of K2SO4 amounts (low amount, K2O 82.57 kg hm-2, LK; moderate amount, K2O 165.07 kg hm-2, MK; high amount, K2O 247.58 kg hm-2, HK) was established to assess the effects of K2SO4 application on the chemical and bacterial characteristics of tobacco-planting soil using 16S rRNA gene and metagenomic sequencing approaches. Results showed that HK led to lower pH and higher nitrogen (N), potassium (K), sulfur(S) and organic matter contents of the soil than LK. The bacterial community composition of HK was significantly different from those of MK and LK, while these of MK and LK were similar. Compared to LK, HK increased the relative abundance of predicted copiotrophic groups (e.g. Burkholderiaceae, Rhodospirillaceae families and Ellin6067 genus) and potentially beneficial bacteria (e.g. Gemmatimonadetes phylum and Bacillus genus) associated with pathogens and heavy metal resistance, N fixation, dissolution of phosphorus and K. While some oligotrophic taxa (e.g. Acidobacteria phylum) related to carbon, N metabolism exhibited adverse responses to HK. Metagenomic analysis suggested that the improvement of pathways related to carbohydrate metabolism and genetic information processing by HK might be the self-protection mechanism of microorganisms against environmental stress. Besides, the redundancy analysis and variation partitioning analysis showed that soil pH, available K and S were the primary soil factors in shifting the bacterial community and KEGG pathways. This study provides a clear understanding of the responses of soil microbial communities and potential functions to excessive application of K2SO4 in tobacco-planting soil.

Evaluation of the impact of potassium solubilizing bacteria on potassium efficiency and yield of canola under saline and non-saline soil conditions

ABSTRACT Canola (Brassica napus L.) is one of the most important oilseed crops used globally for nutritional and industrial purposes. In the pursuit of sustainable agriculture goals, understanding plant-microbe interactions is necessary. This study aimed to evaluate the effects of seven levels of potassium sulfate fertilizer (K2SO4; 0, 25, 50, 75, 100, 125 and 150 kg ha−1), which at each of the following five potassium solubilizing bacteria (KSB; non-inoculated, Pantoea agglomerans, Rahnella aquatilis, co-inoculation (P. agglomerans+R. aquatilis) and a commercial biofertilizer ‘PotaBarvar-2’), on potassium uptake and yield of canola under saline and non-saline soil conditions. The results indicated that among KSB treatments, the highest values for all traits were observed when P. agglomerans and R. aquatilis together were applied, which could be considered as the best KSB treatment in both soil conditions. However, grain yield was increased by 39.7% (1226.4 kg ha−1) and 51.1% (1325.0 kg ha−1); the application of K2SO4 was reduced by 13.3% (10.9 kg ha−1) and 12.4% (13.9 kg ha−1) when the co-inoculation compared to the non-inoculated treatment under non-saline and saline soil conditions, respectively. Consequently, the application of P. agglomerans and R. aquatilis together can be recommended in sustainable canola production systems, particularly under saline soil conditions.

Microbial activity and carbon rates the soil in response to the application of potassium sources

The continuous use of KCl may not be sustainable in the long term in agricultural systems. High doses used in crops accumulate in the soil and plants, hindering the metabolic processes of soil organisms. This study assessed the soil microbial activity in response to the application of K sources in banana crop and effects on microbial C. The experimental design was completely randomized with four K sources: potassium nitrate (KNO3), potassium chloride (KCl), potassium sulfate (K2SO4), and monopotassium phosphate (KH2PO4) at 200 mg kg-1 of K2O, besides the control (without K) and combinations KCl:K2SO4. KCl application increased microbial activity 7 days after incubation, with gradual reduction over time. The isolated application of K2SO4 and the combination KCl: K2SO4 at the ratio 60: 40% increased total CO2 released by the microbiota. K2SO4 source had the highest microbial biomass C (MBC), as well as the 60: 40 combinations. Isolated application of K sources, especially with high chloride concentration, reduces the soil microbial activity and MBC.

Investigating the role of potassium and urea to control fruit drop and to improve fruit quality of “Dhakki” date palm

Fruit drop is a key issue with date palm cultivars that can be addressed with a variety of methods and strategies. Foliar application of macronutrients can be more effective in inhibiting fruit drop and improving the quality of date fruits. The current study was carried out to investigate the possible role of potassium (K) and urea to reduce fruit drop and improve the fruit quality of “Dhakki” date palm. It was conducted in a complete randomised block design with seven treatments and three replications at Pakistan's Agricultural Research Institute, Dera Ismail Khan. The treatments used were: (i) Control (distilled water spray); (ii) Potassium sulphate (K2SO4) at 1 %; (iii) K2SO4 at 1 % + Urea at 2 %; (iv) K2SO4 at 2 %; (v) K2SO4 at 2 % + Urea at 2 %; (vi) K2SO4 at 3 % and; (vii) K2SO4 at 3 % + Urea at 2 %. All the concentrations were sprayed at Kimri stage of fruit development during two consecutive growing seasons. Twenty-one date palms of equal size and age were chosen for the assessments to measure percent fruit drop and other physicochemical variables, including fruit length, fruit diameter, fruit weight, pulp percentage, yield/bundle, pH, total soluble solids (TSS), K content in fruit, and all sugars (percent) of harvested date fruit. The results revealed that bunch spray of K significantly affected all the parameters during both seasons. Application of K2SO4 alone and in combination with urea not only effectively reduced the fruit drop but also improved fruit quality in date where, K2SO4 applied at 2 % combined with urea was the best concentration in reducing fruit drop, enhancing other physicochemical attributes, and improving fruit quality of “Dhakki” date palm. This study may effectively contribute to reduce the fruit drop and enhance the fruit quality by using K and urea, enabling farmers to improve the date yield and increase economic growth.

The Effect of Foliar Application of K2SO4 or KH2PO4 on Skin Color of the ‘Kyoho’ Grape

Anthocyanins in red grape skin have a positive effect on fruit color and human health. The effect of foliar potassium application on anthocyanin accumulation in grape skin is not well understood. The study aimed to better understand the mechanism of anthocyanin accumulation in grape skin in response to foliar sprays of K2SO4 and KH2PO4. In this study, we investigated the effects of foliar application of KH2PO4 (T2), K2SO4 (T1) and distilled water (CK) on the skin color of ‘Kyoho’ grapes at mid-ripe and mature stages. At 90 and 110 days after full bloom (DAFB), T2 had the greatest total soluble solids (TSS), flavonoid and total anthocyanin contents, followed by T1 and CK. At two stages, the titratable acid content decreased and the juice pH increased under T2 treatment relative to CK. T1 and T2 had lower lightness (L*) than CK, and the color index of red grapes (CIRG) under T1 and T2 increased at two stages compared to CK. KEGG metabolic pathway analysis revealed that flavonoid biosynthesis was the most significantly enriched pathway in CK vs. T2 at 90 and 110 DAFB. At 90 DAFB, T2 had higher expressions of phenylalanine ammonia-lyas (PAL), cytochrome P450 CYP73A100 (CYP73A), 4-coumarate: CoA ligase (4CL), chalcone synthase (CHS), flavanone 3-dioxygenase-like (F3H) and UDP glucose: flavonoid 3-o-glucosyl transferase (UFGT) than CK and T1. Foliar application of potassium fertilizer may accelerate anthocyanin accumulation by altering the transcript levels of PAL, CYP73A, 4CL, CHS, F3H, and UFGT of the flavonoid biosynthesis.

FOLIAR APPLICATION OF POTASSIUM AND ZINC ENHANCES THE PRODUCTIVITY AND VOLATILE OIL CONTENT OF DAMASK ROSE (Rosa damascena Miller var. trigintipetala Dieck)

Potassium (K) levels are decreasing worldwide in agricultural soils, and K deficiency is becoming a major issue. Study on damask rose response to K application is scarce. Furthermore, despite its importance in the cell division, photosynthesis and protein synthesis, there is a lack of published reports on plant responses to zinc (Zn) application. Further research is required to understand the damask rose's response to both elements. This study investigated the effects of K and Zn foliar application on the vegetative growth, flower yield, and volatile oil content and composition of damask rose. K and Zn nutrition was applied either individually or combined as K2SO4 and ZnSO4 at 0.5 or 1.0%. Foliar application of K2SO4 and ZnSO4 was applied with a manual pump four times in each growing season, the first at the beginning of stem elongation and leaf formation, and then at two-weekly intervals. Results showed that K and/or Zn treatments significantly improved the growth characters, flower yield, relative water content (RWC), stomatal conductance, and essential oil content and composition such as linalool, nerol, citronellol, geraniol, and nonadecane. The chlorophyll content, total soluble sugars (TSS), and protein content also increased, but free amino acid content decreased, suggesting that the distribution of nitrogenous compounds (between amino acids and proteins) and their transformation were influenced by K and Zn supply. Individual applications of K or Zn increased the N, P, K, and Zn contents in damask rose leaves, relative to the control, which increased further with combined applications of K and Zn. Results suggest that foliar application of K and/or Zn could be part of the damask rose fertilization program to provide plants with the optimum level of nutrition for improving the quantity and quality of flowers and essential oil yields.

Foliar Potassium Sulfate Application Improved Photosynthetic Characteristics, Water Relations and Seedling Growth of Drought-Stressed Maize

Changing climates and frequent spells of drought have increased the risk of crop failure, especially in arid and semi-arid regions, thus multiplying the vulnerability of food-insecure populations. The exogenous application of potassium (K) can potentially ameliorate the adverse effects of drought in maize by maintaining cell osmotic potential and turgidity, provided its optimum doses are applied. The present experiment comprised two maize cultivars, viz. Islamabad Gold (drought tolerant) and Azam (drought susceptible), grown under well-watered (80% water-holding capacity (WHC)), mild drought (60% WHC) and severe drought (40% WHC) conditions. Different doses of K, viz. 0%, 1% and 2%, were also tested to screen out the most superior concentration. Drought stress markedly reduced root and shoot lengths (25% and 16%, respectively) along with their dry weights (20% and 10%, respectively). Moreover, a substantial reduction in leaf relative water content (RWC) (24%), stomatal conductance, transpiration and photosynthesis rates, chlorophyll pigments a, b and total chlorophyll contents (31%) were recorded, compared with well-watered conditions. However, foliar application of K2SO4 at 2% concentration outperformed other doses by improving growth attributes, RWC (10%), total chlorophyll (9%) and proline (12%) under severe drought conditions. Our findings confirmed the effectiveness of foliage-applied K2SO4 in ameliorating drought effects in rainfed maize; however, more doses and sources of K could be tested for developing it as a potent source to cope with water stress.

Silicon Compounds and Potassium Sulfate Improve Salinity Tolerance of Potato Plants through Instigating the Defense Mechanisms, Cell Membrane Stability, and Accumulation of Osmolytes

ABSTRACT Potato (Solanum tuberosum L.) as a strategic crop is moderately susceptible to salinity. Therefore, it is essential to recognize the defense mechanisms upon which potato plants respond to salinity stress and adopt strategies to enhance their salinity tolerance. An open field experiment was conducted at different saline irrigation water (0.5, 5, 8, and 12 dS.m−1) to investigate the physicochemical traits and tuber yield of potato plants under antistress compounds application, including K2SO4, NaSiO3 nanoparticles (NaSiO3-NPs), and SiO2. The results showed that gas exchange variables were suppressed by salinity stress, while they were alleviated by foliar application of K2SO4. The lowest leaf malondialdehyde content was observed at 5, and 12 dS.m−1 in SiO2 and NaSiO3-NPs-treated plants showed 56% and 43% decreases, respectively, over control. The application of silicon under saline conditions increased leaf soluble carbohydrates and proline content compared with the control. While salinity increased the Na+/K+ ratio, the application of silicon reduced Na+/K+ more than twice compared with the control. The antioxidant enzyme activities were induced the most by NaSiO3-NPs. It seems that the use of antistress compounds, especially nanoparticles, would be a practical approach to alleviate the detrimental effects of salinity stress on potato plants.

Exogenous Potassium Treatments Elevate Salt Tolerance and Performances of Glycine max L. by Boosting Antioxidant Defense System under Actual Saline Field Conditions

Salinity is one of the major issues that limits field crop productivity in an arid and semiarid environment. Therefore, two field trials were carried out over two seasons of 2018 and 2019 to investigate the enhancement of different methods of potassium application (i.e., recommended soil amendment (control; K2O), seed soaking (SS) and foliar spray (FS) in the form of potassium sulfate (K2SO4, 6 mM)) on antioxidant protection, physio-biochemical, yield and quality traits of soybean (cv. Giza 22) grown in normal (electrical conductivity; EC = 2.68 dS m−1) and saline soil (EC = 7.46 dS m−1). Physio-biochemical attributes (total chlorophyll, carotenoids, K+ and K+/Na+ ratios, performance index and catalase (CAT) activity), growth traits (i.e., shoot length, number and area of leaves plant−1 and shoot dry weight), yield and its components and seed quality (number of pods plant−1, 100-seed weight, seed yield ha−1 and seed protein and oil contents) were significantly decreased when soybean plants were grown in saline soil compared with those grown in normal soil. In contrast, activity of enzymatic antioxidants (i.e., superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione peroxidase (GPX)), contents of non-enzymatic antioxidants and osmoprotectants (i.e., total soluble sugars, free proline, ascorbic acid and α-tocopherol), Na+, Cl−, H2O2 and malondialdehyde (MDA) were increased in soybean plants grown in saline soil compared with normal soil. However, under salt-stressed conditions, potassium applied through SS or FS significantly enhanced all soybean growth, photosynthetic efficiency, K+ content, ratio of K+/Na+ and activity of CAT, SOD, APX and GPX as well as improved yield and quality traits, while potassium application did not affect the contents of non-enzymatic antioxidants and osmoprotectants. For instance, foliar potassium application (FS) increased seed yield ha−1 by 92.31% and protein content by 63.19% compared with the control under the salt stress condition. In addition, both applications of potassium significantly reduced Na+, Cl−, H2O2 and MDA contents in soybean plants compared with those obtained from control treatments. Exogenous application of K2SO4 was more effective than SS at improving soybean physio-biochemical attributes, yield and seed quality traits under soil-salinity stress.

Control of pre-harvest application of certain chemicals ripening on guava

Fruit ripening is a natural process in which a fruit goes through various physical and chemical changes and gradually becomes sweet, coloured, soft and palatable. However, this natural process can also be stimulated by using artificial fruit ripening agents. Farmers and vendors often use artificial ripening agents to control fruit ripening rate. Different fruit ripening agents can be used to ripen fruits artificially and to provide fruits the desired color and taste within a short time. In recent years, the use of artificial fruit ripening agents is becoming much prevalent, the agents being mostly used for commercial purposes. During winter months ripening of guava is big problem due to low temperature. Ripening in guava fruit is irregular and follows over a prolonged period needing multiple harvests, thus hike in the cost of production. In other words, ripening is the process by which they attain a good flavor, quality, color and other textural properties. The reason for textural fruit changes and the fruit softening is the cell structure. Objectives: Some phytohormones like ethylene are responsible for the fruit ripening. Certain PGRs can modify the perception, content, or action of such phytohormones, possibly fast-tracking fruit ripening process. To enhance ripening different substances are used. The effects of two ripening chemicals, ethephon and potassium sulphate on ripening process, are discussed in this review paper. Application of ethephon at 400-500 ppm on guava fruit on the plant, accelerated ripening. Ethephon generally slightly alter the fruit quality characteristics. Similarly observations were recorded when potassium sulphate is applied as pre harvest application. It has been reported that the foliar application of K2SO4 @ 3% provides encouraging results for quality improvement guava fruit.

Potassium Influencing Physiological Parameters, Photosynthesis and Sugarcane Yield in Subtropical India

Potassium plays an important role in the metabolism of plants, growth, development and yields. Worldwide, KCl is commonly used as source of K fertilizer in agricultural crops. The present experiment was taken up to assess the response of various sources of K on physiological attributes, yield and quality parameters of sugarcane. Treatments were no K application, potassium ammonium sulphate (H4KNO4S-9:0:30:20, NPKS ratio), slow release K fertilizer (0:0:45:0), sulphate of potash/potassium sulphate (K2SO4-0:0:50:17.5), muriate of potash (KCl-0:0:50:0) and muriate of potash (KCl) + elemental S @ 40 kg ha−1. Application of K2SO4 recorded 15.8% improvement in tiller population (during peak tillering stage) and 22.2% improvement in dry matter accumulation (at the harvest stage) over the KCl. About 12.33–24.16% increments in crop growth rate and the highest net photosynthetic rate (19.91 µmol m−2 s−1) were also recorded with application of K2SO4. Application of K fertilizers improved the availability of potassium in soil by 8.17% (254.2 kg ha−1). Potassium uptake in sugarcane crop ranged from 245 to 347 kg ha−1. The highest individual cane length (311 cm) was measured with application of K2SO4. Application of K2SO4 brings forth about 23.8% increments in millable canes, 14% in cane weight and 33.8% in cane yield over no K. Application of K also increased mean sucrose content in juice by 0.58 unit (17.0 pol per cent juice) over no use of K. Overall effect of K application on increasing sugarcane yield and sucrose content simultaneously brought forth improvement in commercial cane sugar (CCS) by 29.43% (10.50 t/ha) over no use of K. However, application of K2SO4 also improved CCS by 25.89% (11.67 t/ha) over the application of KCl.

Enhancement of frost tolerance of almond flowers using potassium

Using mineral nutrients is recommended as a plan to alleviate or avoid spring frost damage to blossoms. The purpose of this study was to investigate the effects of potassium application on reducing or preventing spring frost damage of almond (Prunus dulcis Mill.) flowers. Treatments were four levels of K2SO4 (0, 1, 2, and 4%). The nutrition solutions were sprayed on trees in two times (bud swell stage and green tip stage) in 2018–2019. The spurs containing flower buds were collected during the full blooming phase. The spurs segments were exposed to three different freeze test temperatures (0, −2, and −4 °C), and some relevant physiochemical changes were evaluated. The application of K2SO4, especially 4% K2SO4, decreased freezing injury, electrolyte leakage percentage, hydrogen peroxide (H2O2), and malondialdehyde (MDA) concentrations of flowers after freezing tests compared with control. The nutrient treatments, especially 4% K2SO4, increased significantly the contents of soluble proteins, soluble carbohydrates, total phenolic compounds, and proline of flowers. The results of the present study could have implications for the use of potassium in freezing tolerance improvement of other temperate fruit trees grown in low temperatures regions.

K Fertilizers Reduce the Accumulation of Cd in Panax notoginseng (Burk.) F.H. by Improving the Quality of the Microbial Community.

The high background value of cadmium (Cd) in the Panax notoginseng planting soil is the main reason for the Cd content in P. notoginseng exceeding the limit standards. The main goal of this study was to reveal the mechanism by which potassium (K) reduces Cd accumulation in P. notoginseng from the perspective of the influences of soil microbial communities on soil pH, total organic matter (TOM) and cation exchange capacity (CEC). Pot experiments were conducted to study the effects of different types and amounts of applied K on the Cd content in P. notoginseng, and on the soil pH, TOM, CEC, and bioavailable Cd (bio-Cd) content in soil. Field experiments were conducted to study the effects of K2SO4 fertilizer on the microbial community, and its correlations with the soil pH, TOM and CEC were analyzed. A moderate application of K2SO4 (0.6 g⋅kg–1) was found to be the most optimal treatment for the reduction of Cd in the pot experiments. The field experiments proved that K fertilizer (K2SO4) alleviated the decreases in pH, TOM and CEC, and reduced the content of bio-Cd in the soil. The application of K fertilizer inhibited the growth of Acidobacteria, but the abundances of Mortierellomycota, Proteobacteria and Bacteroidetes were promoted. The relative abundances of Acidobacteria and Proteobacteria in the soil bacteria exhibited significant negative and positive correlations with pH and CEC, respectively. In contrast, the relative abundance of Mortierellomycota was found to be positively correlated with the pH, TOM and CEC. The bio-Cd content was also found to be positively correlated with the relative abundance of Acidobacteriia but negatively correlated with the relative abundances of Proteobacteria and Mortierellomycota. The application of K fertilizer inhibited the abundance of Acidobacteria, which alleviated the acidification of the soil pH and CEC, and promoted increase in the abundances of Mortierellomycota, Proteobacteria and Bacteroidetes, which ultimately increased the soil TOM and CEC. Soil microorganisms were found to mitigated decreases in the soil pH, TOM, and CEC and reduced the bio-Cd content in the soil, which significantly reduced the accumulation of Cd in P. notoginseng.

Effects of Potassium and Humic Acid on Amelioration of Soil Salinity Hazardous on Pea Plants

Pots experiment were carried out in green house of National Research Centre, Dokki, Egypt, to study the effect of potassium and humic acid application to minimize the adversely effects of soil salinity on pea plants. Pots were divided into three main groups of soil salinity at levels (2.84, 6.03 and 8.97 dS m-1). These main groups were applied potassium sulfate at the rates 50 and 100 kg fed-1. Foliar application of humic acid was applied at a rate of 0.2%. Data presented that the application of K2SO4 at a rate of 100 kg fed-1 with humic acid a foliar spray at a rate of 0.2%, gave the highest values of plant growth parameters such as, Branch No., Leave No., Plant height, leaf area, Shoot fresh and dry weight. In addition to produce high chlorophyll a and b and carotene content as compared to other treatments and control under the different soil salinity levels. Application of K2SO4 (100 kg fed-1) with foliar spray of humic acid under high and moderate soil salinity condition increased pod weight, seed weight, seed dry weight over application of 50 kg fed-1 and control. The highest values of studied chemical constituents in shoots and greens were obtained due to the application of potassium sulfate at100 kg fed-1 with humic acid. The combined effects of potassium application and foliar spray of humic acid had a positive effect on increasing the ability of pea plant tolerance to soil salinity and increasing of growth and yield production under saline soil conditions.

Growth Characteristics and Fruit Quality of Chili Pepper under Higher Electrical Conductivity of Nutrient Solution Induced by Various Salts

Salinity as a global challenge is a very complex issue in agricultural food production. In this study, the growth characteristics of chili pepper (Capsicum annuum var. crusader) were evaluated under higher Electrical Conductivity (EC) (5 dS/m) induced by NaCl, KCl, K₂SO₄ or “All Nutrients” of Hoagland nutrient solution. The standard Hoagland solution (with EC 1.8 dS/m) was used as the control. The results showed that EC5 induced by NaCl resulted in the most negative effects on growth, yield and fruit quality parameters. Application of KCl (to induce EC5) also resulted in some reduction in growth parameters. However, application of K₂SO₄ and particularly “All Nutrients” (to induce EC5) resulted in better growth characteristics compared to plants treated with NaCl or KCl salts. There was a significant reduction in growth and fruit quality traits including plant height, leaf SPAD value, fresh and dry weights of shoots and roots, fruit fresh yield, fruit total soluble solids (TSS) and vitamin C content by NaCl and to lesser extent by KCl. However, there was no significant reduction in these traits by “All Nutrients” and for some traits by K₂SO₄ application compared to control plants.

Sulfate-mediated Drought Tolerance in Maize Involves Regulation at Physiological and Biochemical Levels

Restriction in nutrient acquisition is one of the primary causes for reduced growth and yield in water deficient soils. Sulfur (S) is an important secondary macronutrient that interacts with several stress metabolites to improve performance of food crops under various environmental stresses including drought. Increased S supply influences uptake and distribution of essential nutrients to confer nutritional homeostasis in plants exposed to limited water conditions. The regulation of S metabolism in plants, resulting in synthesis of numerous S-containing compounds, is crucial to the acclimation response to drought stress. Two different experiments were laid out in semi-controlled conditions to investigate the effects of different S sources on physiological and biochemical mechanisms of maize (Zea mays L. cv. P1574). Initially, the rate of S application in maize was optimized in terms of improved biomass and nutrient uptake. The maize seedlings were grown in sandy loam soil fertigated with various doses (0, 15, 30 and 45 kg ha−1) of different S fertilizers viz. K2SO4, FeSO4, CuSO4 and Na2SO4. The optimized S dose of each fertilizer was later tested in second experiment to determine its role in improving drought tolerance of maize plants. A marked effect of S fertilization was observed on biomass accumulation and nutrients uptake in maize. In addition, the optimized doses significantly increased the gas exchange characteristics and activity of antioxidant enzymes to improve yield of maize. Among various S sources, application of K2SO4 resulted in maximum photosynthetic rate (43%), stomatal conductance (98%), transpiration rate (61%) and sub-stomatal conductance (127%) compared to no S supply. Moreover, it also increased catalase, guaiacol peroxidase and superoxide dismutase activities by 55, 87 and 65%, respectively that ultimately improved maize yield by 33% with respect to control under water deficit conditions. These results highlight the importance of S fertilizers that would likely be helpful for farmers to get better yield in water deficient soils.