Abstract potassium (K) plays a vital role in increasing the tobacco yield and controlling important quality parameters such as leaf combustibility. The forms of soil K in order of their availability for plants are soil soluble, exchangeable, non-exchangeable and structural potassium. Plant availability of soil K is controlled by dynamic interactions among its different K pools in soil that understanding of these dynamics leads to management of soil fertility. Quantity-Intensity (Q/I) curves of potassium and Q/I parameters provide general information about soil K availability and fertilizers management. This investigation was conducted to study the K forms status and its relationship with Q/I parameters in tobacco cultivated soil in the northwest of Iran. Sorption isotherm was constructed in the laboratory by equilibrating and shaking 2.5 g soil with 25 ml of 0.01 M CaCl2 containing 0-200 mg K L-1 for 24 h. After equilibrium, remaining concentration of K measured and K Quantity-Intensity (Q/I) curves and their parameters such as K buffering capacity (PBCK), K activity ratio at equilibrium (AReK), energy of exchange (EK), the Gapon selectivity coefficient (KG), initial equilibrium concentration of solution K (EKC), readily exchangeable K (∆K0), specific K sites (KX), readily exchangeable K (∆K0) and specific K sites (Kx) were calculated. The soluble, exchangeable, non-exchangeable and structural K forms in 30 soil samples taken from tobacco-growing soils in north-west of Iran, were measured. Soil potassium forms relationships with each other, Q/I parameters and soil physical and chemical characteristics were investigated. The mean of soluble, exchangeable, non-exchangeable and structural K forms in soil samples were 23 (ranged from 10 to 118), 207 (ranged from 64 to 511), 569 (ranged from 443 to 690) mg kg-1, respectively. There were significant correlations among K forms except for solution K. The clay values had a significant and positive correlation with each of K forms except solution K values. The means of PBCK, AReK, ∆K0 and KX values were 10.2 cmol kg-1/(mol L-1)0.5, 0.00476 (mol L-1)0.5, 0.032 and 0.46 cmol kg-1, respectively. The EK values for the check treatments ranged from -5151 to -2128 cal mol-1. The relationship of Kso with exchangeable K was positive (r= 0.42*), but its relationship with pH (r = -0.37*) and CCE (r=0.41*) was significantly negative. There was a significant correlation between solution K and exchangeable K values as well as between exchangeable K and clay values presumably because of exchangeable K depletion in soils that caused to decrease K concentration on tobacco leaf in studied reign. The correlation among exchangeable K, non-exchangeable K, and Kstr values indicated that a part of the non-exchangeable and structural potassium, could be available for the plant during the growing season. It is necessary that consider soil properties such as clay content and clay type by using quantity-intensity relations for potassium fertilizer recommendation.

To determine the effects of sources and rates of potassium on quantitative and qualitative properties of cotton an experiment was conducted in a clay loam soil، with 220 mg. kg-1 available potassium (K). The experiment design was randomized complete block design (RCBD) with three replications and eight treatments as follow: 1-Control (N. P) 2-N. P. K (50 kg. ha-1 K2O before planting as MOP) 3- N. P. K (50 kg. ha-1 K2O before planting as SOP) 4 N. P. K (100 kg. ha-1 K2O before planting as MOP) 5-N. P. K (100kg. ha-1 K2O before planting as SOP) 6- N. P. K (50 kg. ha-1 K2O top dressing as MOP) 7- N. P. K (100 kg. ha-1 K2O top dressing as MOP). Data showed that there was a significant difference in yield among treatments. The highest yield (4091 Kg. ha-1) was obtained by using K as topdressing in flowering stage (treatments no: 6 and 7). Duncan multiple range test showed that there was not a significant effects on yield among treatments No: 1 to No: 5. This means that use of potassium before planting (different amounts and different sources) did not significant effects on yield. Data showed that use of MOP as topdressing increased yield significantly. Use of MOP as topdressing improved cotton fiber quality. Use of 50 Kg. ha-1 K2O produced maximum fiber length (32. 1 mm)، fiber percentage (46%)، fiber strength (4. 29g. tex-1) among treatments. Data also showed that potassium concentration in petiole in this treatment was highest. There were significant correlations between potassium concentration in petiole with yield and with fiber strength. Fertilizer use efficiency was increased due to use of potassium as MOP as top dressing.

Potassium (K) is one of the major essential nutrients for growth of tobacco. Tobacco leaf K content is highly correlated with tobacco leaf quality and is an important index reflecting tobacco leaf quality. The forms of soil Κ in the order of their availability for plants are soil soluble, exchangeable, non-exchangeable and structural potassium. This study aimed to investigate the forms of soil potassium (soluble, exchangeable, non-exchangeable and structural) and aqua-regia extractable potassium in tobacco cultivated areas of Golestan, Mazandaran and Gilan provinces.
Three soil profiles were described and sampled in each tobacco cultivated areas of Golestan, Mazandaran and Gilan provinces. All soil profiles were described and classifid according to Keys to Soil Taxonomy. The soluble, exchangeable, non-exchangeable, structural and aqua-regia extractable potassium were measured and their relationships with each other and soil physical and chemical characteristics were investigated.
Mean concentrations of soluble, exchangeable, non-exchangeable, aqua-regia extractable, structural and total potassium in studied soils were 0 to 38.24, 7 to 513, 44 to 1933, 70 to 4267, 4114 to 15607 and 4166 to 16157 mg kg-1, and the percentage of mean concentarions of soluble, exchangeable, non-exchangeable, aqua-regia and structural potassium to total potassium varied from 0 to 0.32, 0.12 to 4.41, 0.83 to 11.96, 1.21 to 33.72 and 85.60 to 98.96 %, respectively. The lowest concentrations of all potassium forms were measured in the studied soils of Gilan Province. The highest concentrations of soluble, exchangeable, non-exchangeable and aqua-regia extractable K occurred in the studied soils of Mazandaran Province, and structural and total potassium in the studied soils of Golestan Province. The correlation analyses indicated the positive significant correlation (P
Plant available potassium (soluble, exchangeable and non-exchangeable potassium) in Mazandaran province tobacco cultivated areas was more than that in Golestan and Gilan provinces. Therefore, potassium fertilizer management should be different in these areas. Aqua-regia potassium had a good correlation with other forms of potassium. Since contains soluble, exchangeable, non-exchangeable and part of the structural potassium, could show the soil potassium ability for plants during the growing season to be considered, greenhouse and field experiments that need to be examined.

Determination of relationships between different forms of potassium in soils and their constituents can help us to resolve some nutritional problems such as potassium fixation and release and its fertilization management in soil. This investigation was carried out to determine the contribution of soil and their constituents (clay and silt) Kex and Knex to available potassium for plants in 12 loess-like and loess-derived soil series of Golestan province in a pot experiment of corn. Total K uptake of corn in the greenhouse experiment was used as an index of soil-available K. Results showed that the contribution of Kex to plant K uptake was more than that of Knex in clay fraction of all soils. Whereas the contribution of Knex to plant K uptake was more than that of Kex in silt fraction of all soils excluding Oghchi soil series with the highest initial Kex. Therefore, the silt fraction is an important K source for supplying the plant need for K in loess-like and loess-derived soils.

Potassium as an essential plant nutrient plays important physiological roles in plants. Q/I relationships present beneficial information for assessment of plant potassium availability and fertilizer application management. The K quantity-intensity relationships and their parameters; labile K, slowly exchangeable K, potassium activity ratio, potassium activity ratio at equilibrium and potassium buffering capacity were compared using four treatments (potassium chloride, potassium chloride + ammonium chloride, potassium chloride + sodium mono phosphate and potassium chloride + ammonium chloride + sodium mono phosphate) on three soils with different specific surfaces. Soil samples obtained from 0-30 cm top-soils of Rahmat Abad soil series (Gorgan University-Pardis), Lavark (Isfahan) and Salehan village (Khomein). The maximum soil PBCk obtained for Gorgan Uneversity (Pardis). Clay type and soil cation exchange capacity control PBCk and its parameters in these soils. Maximum PBCk was obtained by potassium chloride and minimum by potassium chloride + Ammonium chloride in all soils. The PBCk for potassium chloride + sodium mono phosphate was greater than potassium chloride + ammonium chloride + sodium mono phosphate. Increased sodium salt concentration in solution may increase sodium salt concentration in diffuse double layer and hence PBCk. Since the bulk of water and nutrients are held in truncated diffuse double layers with soils of high specific surface area at field conditions, solution potassium concentration and ARKe may more closely estimate plant available potassium relative to PBCk; also suggesting ARKe as a more relevant index when comparing potassium availability for soils of widely differing specific surface area.

The current study was conducted to investigate the effect of different levels and sources of potassium (K) on seed and oil yields and K uptake of sunflower (Helianthus annuus L.) var. Azargol. The experiment was laid out in randomized complete block design under split plot arrangement with three replications at two locations in West Azerbaijan province during two consecutive years (2017-18). Sunflower sources (K2SO4 and KCl) were arranged in the main plots, accommodating five K doses 0 (control), 100, 200, 300 and 400 kgha-1 in sub-plots. The results indicated that treatment of 100 kgha-1 K from K2SO4 source increased the seed and oil yields by, respectively, 44.8% and 38.6%, which did not differ from the same treatment using KCl. The highest straw weight and biomass were obtained by 300 kg.ha-1 K from K2SO4 source, which increased by 58.9% and 51.8%, respectively, compared to the control. K uptake by straw was 2.93 times more than the grain. Sunflower reduced native available potassium (Kava) by 32 mg.kg-1. K uptake in grain was 141.2 kg.ha-1, which enhanced with increasing potassium level treatments. The soil Kava was proportional to potassium level treatments. The maximum soil Kava was 410 mg.kg-1, with application of 400 kg.ha-1 of K. In this connection, K sourcaes had the same effect. The results suggested that by application of 100 kg K.ha-1  from K2SO4 or KCl in oil-seed sunflower cultivation, in addition to producing a suitable product, Kava of the soil is maintained in optimum range.

Potassium is essential plant macronutrients. According to the conceptual approach soil potassium (K) can be classified into four forms: soil solution K, exchangeable K, fixed K and structural K. In this research, potassium forms were determined in loess and loess like derived soils of Golestan Province and in the silt and clay fractions of them. The objective of this research was to determine the contribution of soil separates in release of potassium and to be fertilizer management in the soils. Mean extracted potassium content in clay particles of all soils was more than that of soil and silt fraction. The quantity of K extracted by HNO3, NH4oAc and HF in soils varied from 632 to 1200, 103 to 476 and 12000 to 17800 mg/Kg, respectively. The mean of exchangeable, nonexchancheable and total potassium contents were 160.6, 1155.1 and 19100 mgKg-1, respectively in clay fraction. The quantity of non exchancheable K extracted from silt fraction was a half of its quantity in clay fraction.

Most growers do not pay attention to the issue of proper nutrition, including the proper ratio of elements in the nutrient solution and changing the concentration of each element and their ratio at different stages growth. Lack of available information in this regard, in the present study, it has been decided to evaluate the effect of different ratios of nitrogen and potassium on the quantitative and qualitative characteristics of tomato fruit under hydroponic conditions. The balance of nutrients in the culture medium is one of the factors affecting the yield and quality of crops and horticulture. The present study was conducted to investigate the effects of different ratios of nitrogen and potassium on the quantitative and qualitative characteristics of Hirad tomato fruit in hydroponic conditions.

Treatments include concentrations of nitrogen and potassium in the vegetative and reproductive period including 1) nitrogen and potassium at concentrations of 130 and 250 ppm in the vegetative stage and 160 and 350 ppm in the reproductive stage; 2) nitrogen and potassium at concentrations of 140 and 260 ppm in the vegetative stage and 170 and 360 ppm in the reproductive stage, respectively; 3) nitrogen and potassium at concentrations of 150 and 270 ppm in the vegetative stage and 180 and 370 ppm in the reproductive stage, respectively; and 4) nitrogen and potassium were at concentrations of 160 and 280 ppm in the vegetative stage and 190 and 380 ppm in the reproductive stage, respectively.

The results showed that the nutrition of tomato plant with different ratios of nitrogen and potassium affects different characteristics of the plant such as quantitative and qualitative indicators. The highest stem diameter value was obtained in the vegetative and reproductive stages in treatment 3. Treatment 2 showed the highest yield of single plant, total acid and fruit lycopene, and in treatment 4, the highest amount of fruit chlorophyll and soluble solids was observed.

Also, the highest ascorbic acid content was obtained in treatment 1.In general, in order to achieve maximum yield and improve the quality of tomato fruit, it is recommended to use more potassium and less nitrogen.

Potassium (K) as a macroelement is frequently made available by weathering of aluminosilicates such as K-feldspar and micaceous minerals in the soils. The objectives of this study were to determine the effect of mineral grain size and type of extractant on the different forms of K of micaceous and K-feldspar minerals and to find out a relationship between aqua-regia extractable K and type of K-bearing minerals. Water soluble, exchangeable, non-exchangeable and aqua-regia exteractable K of 50-100 and <50 μm sizes of biotite, phlogopite, muscovite, zanjan and yazd K-feldspars were investigated. The amount of released K was measured by flame photometer. The results indicated that the amounts of soluble and exchangeable K of trioctahedral micas (biotite and phlogopite) and feldspars are not greatly different, but in this regards, diotahedral muscovite is less important even than feldspars. Soil reservoir of non-exchangeable potassium is significantly higher in trioctahedral micas (up to 17 g kg-1) than muscovite and feldspars (up to 3 g kg-1). The small particles (<50 μm) had a significant effect on the different forms of K in all minerals. The amount of aqua-regia extractable K from trioctahedral micas exceed to 81 g kg-1. This value was 4 g kg-1 for other minerals. The mineral size had no effect on the aqua-regia extractable K in trioctahedral micas while in muscovite and feldspars this form of K increase up to 3.5 times with particle size reduction. More investigations are necessary to propose aqua-regia extractable K as an indicator for assessing type and amount of K-bearing minerals and soil potassium supplying power.

Glauconite is a micaceous mineral that could be source of potassium. The aim of this study was evaluation of the effects of glauconitic sandstone and potential of iron relase and toxicity in case of using as a potassium fertilizer for canola plants. The plants cultivation experiments were carried out in growth chamber in sand culture with completely randomized design as factorial. The first factor was potassium with three levels including Hoagland nutrient solution, Hoagland nutrient solution lack of potassium and Hoagland nutrient solution lack of potassium accompanied with glauconitic sand stone powders. The second factor was pH of culture medium contained 6 and 7.5. The results indicated that potassium deficiency in Hoagland nutrient solution without potassium treatment caused severe reduction in growth traits, contents of K+, soluble protein, starch and chlorophylls and increased total amino acids in canola plants. Application of glauconitic sand stone powders could release potassium in solution medium as plants treated with Hoagland without + glauconite did not indicated significant differences in fresh and dry mass and potassium content with Hoagland-treated ones. Iron content was higher in roots of Hoagland without potassium + glauconite treated canola plants compared treatments, however, pH reduction from 7.5 to 6 did not increase iron content in this treatment. The reduction of pH of nutrient medium imposed significant decrease of soluble protein, starch and chlorophyll contents that lead to growth retardation of canola plants. The results indicated that glauconitic sandstone has certain potential to release potassium. Iresspective pH of nutrient solution, no toxicity symptom was observed in canola plants following glauconite application.