Changes in some chemical properties of saline-sodic soils over time as affected by organic residues: An incubation study

Salinization and sodification of agricultural lands in arid and semi-arid regions of the world are two limiting factors in the crop production. This study was conducted to evaluate the effect of readily available agricultural residues on changing some chemical properties of saline-sodic soils. Wheat, potato, sunflower, and canola residues were separately added into three saline-sodic soils at a rate of 2% by weight and thoroughly mixed with soils. Control and treated soils were incubated for 168 days at a constant moisture and temperature. The pH, electrical conductivity (EC), soluble cations, available nitrate (NO3-) and phosphorous (P), cation exchange capacity (CEC), and exchangeable sodium percentage (ESP) were measured during the incubation. The EC increased in the response to the incorporation of plant residues, whereas the pH was reduced. The application of organic components in soils increased CEC and decreased ESP. The results showed that the maximum reduction in ESP was observed in the potato treatment because of the highest Ca2+ concentration. The average reduction in ESP of treated soil samples at the end of incubation followed this order: 16.1% (potato residue-treated soil) >12.7% (canola residue-treated soil) >11.1% (wheat residue-treated soil) >9.6% (sunflwer residue-treated soil). The potato residue was the most effective amendment in changing the chemical properties of saline-sodic soils in comparison with other organic residues. The results indicated that the application of organic residues had a positive impact on reducing the soil sodicity and improving the soil fertility depending on their chemical composition

Guanidinium (aqua-2κO)(4-hydr­oxy-6-carboxy­pyridine-2-carboxyl­ato-2κ3 O 2,N,O 6)(μ-4-hydroxy­pyridine-2,6-dicarboxyl­ato-1:2κ4 O 2,N,O 6:O 2)(4-hydroxy­pyridine-2,6-dicarboxyl­ato-1κ3 O 2,N,O 6)dizincate(II) dihydrate

The title compound, (CH6N3)[Zn2(C7H3NO5)2(C7H4NO5)(H2O)]·2H2O, has an anionic binuclear complex of ZnII balanced with a guanidinium cation. There are two uncoord­inated water mol­ecules in the structure. The asymmetric unit of the compound has two different coordination types (the coordination of Zn1 is distorted trigonal-bipyramidal, while that of Zn2 is distorted octahedral) of ZnII in the crystal structure that are bridged to each other via one hypydc2− group (hypydcH2 is 4-hydroxy­pyridine-2,6-dicarboxylic acid). A variety of inter­molecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds involving water mol­ecules, cations and anions, and also a weak π–π inter­action [3.798 (1) Å], are responsible for extending the structure into a three-dimensional network

catena-Poly[[[aqua­cadmium(II)]bis­(μ-4-hydroxy­pyridine-2,6-dicarboxyl­ato)[aqua­cadmium(II)]di-μ-aqua] tetra­hydrate]

The title polymeric compound, {[Cd2(C7H3NO5)2(H2O)4]·4H2O}n or {[Cd2(hypydc)2(H2O)4]·4H2O}n (where hypydcH2 is 4-hydroxy­pyridine-2,6-dicarboxylic acid), was synthesized by the reaction of cadmium(II) nitrate hexa­hydrate with 4-hydroxy­pyridine-2,6-dicarboxylic acid and propane-1,3-diamine, in a 1:2:2 molar ratio in aqueous solution. The compound is a seven-coordinate binuclear polymeric complex with distorted penta­gonal bipyramidal geometry around CdII [Cd—O = 2.247 (4)–2.474 (3) Å]. In the binuclear monomeric units, the central atoms join together by O atoms of two bridging tridentate (hypydc)2− ligands, and the polymer propagates via two bridging water mol­ecules that link each CdII centre of one monomer to the adjacent neighbour. Propane-1,3-diamine (pn) does not appear in the product but plays a role as a base. Inter­molecular O—H⋯O and C—H⋯O hydrogen bonds, and π–π stacking inter­actions, with distances of 3.725 (3) and 3.766 (3) Å, connect the various components

Selectivity and Adsorption of Potassium by Bentonites Saturated with Calcium, Magnesium and Sodium

IntroductionThe relative preference and the cation exchange capacity of the exchanger are among the important and determining factors in the adsorption and retention of cations. Studies have shown that factors such as valency, the size of the hydrated radius or the relative hydration energy of ions, the type of clay mineral, the concentration of the solution phase, the amount of organic matter, the structural characteristics, and the charge density of the exchanger determine the preferential adsorption of cations in the soil. The aims of this study were: 1) to investigate the effect of contact time, adsorbent dose, and pH on potassium selectivity by bentonite in binary systems including K-Ca, K-Mg, and K-Na based on Gapon, Vanslow, and Gaines-Thomas equations and 2) to investigate the potassium adsorption isotherms by bentonites saturated with calcium, magnesium, and sodium.Materials and MethodsTo saturate bentonite, 1 M solutions of calcium, magnesium, and sodium chloride were separately used. The effects of contact time (10-1440 min), adsorbent dose (0.1-2 g), and pH (3-9) on potassium adsorption and selectivity by bentonites saturated with calcium, magnesium, and sodium in binary systems were investigated. In these experiments, 20 mL of a solution containing 24 meq L-1 of potassium and 6 meq L-1 of the competing cation (Ca, Mg, or Na) were added to the adsorbent. The selectivity coefficients of Gapon, Valselow, and Gaines-Thomas were calculated. Isotherm experiments were also performed to evaluate the effect of different equivalent fractions of potassium (0.1, 0.2, 0.4, 0.6, 0.8, 0.9, and 1) and the competing cation in the solution phase on potassium adsorption. Simple linear, Freundlich, and Temkin equations were fitted to the isotherm data.Results and DiscussionThis study results showed that the adsorption of potassium by Ca-, Mg-, and Na-bentonites increased with increasing contact time and reached its highest value in 24 hours. The pseudo-second-order kinetic equation was better able to describe the process of potassium adsorption by bentonites over time than the pseudo-first-order equation. Potassium adsorption by Mg- and Na-bentonites had a downward trend with increasing the absorbent dose in the range of 0.1-2 g, while Ca-bentonite showed the highest adsorption of potassium in the dose of 0.2 g. With increase in pH, the percentage of potassium adsorbed from the solution phase increased; and reached its maximum value at pH 9. The amount of potassium adsorption by Mg- and Na-bentonite in all pHs was almost the same and at the same time more than Ca-bentonite. The interesting result of this research was that the behavior of Mg-bentonite was more similar to Na-bentonite than to Ca-bentonite. An increase in the negative charge of aluminosilicates with an increase in pH can occur due to the loss of protons by silanol and aluminol groups. The selectivity coefficients of Gapon, Vanslow, and Gaines-Thomas changed under the influence of contact time, adsorbent dose, and pH. Comparing the results of the investigation of the mentioned factors with the results of the selectivity coefficients showed that these coefficients cannot be a definitive criterion for judging the preference of one cation over another cation for adsorption in exchange sites. The isotherm experiment indicated that the amount of potassium adsorption in the solid phase increased with the increase of the potassium equivalent fraction in the solution phase; so the maximum adsorption was observed at the highest initial concentration of potassium (30 meq L-1, which corresponded to the equivalent fraction of 1). The linear adsorption coefficient in the simple linear equation (Kd) showed that potassium adsorption by Na-bentonite was higher than the two others. The highest amount of Kd, 56.0 L kg-1, and the lowest value, 11.9 L kg-1, were obtained for bentonites saturated with sodium and calcium, respectively. The parameter bT, the heat of exchange in the Temkin equation, was estimated to be 4.5, 5.0, and 19.1 (J mol-1) for bentonites saturated with sodium, magnesium, and calcium, respectively. Three simple linear equations, Freundlich, and Temkin were able to describe the adsorption process well. However, based on the highest value of the coefficient of determination (R2) and the lowest value of the standard error (SE), it can be said that the Freundlich equation showed the best fit to the data.ConclusionThe highest adsorption of potassium occurred at a contact time of 24 h, a dose of 0.1 g for Mg- and Na-bentonite and 0.2 g for Ca-bentonite and pH 9. The pseudo-second-order equation described well the kinetics of potassium adsorption by bentonites over time. The results showed that the behavior of Mg-bentonite was more similar to Na-bentonite than Ca-bentonite. The selectivity coefficients of Vanslow, Gaines-Thomas, and Gapon changed under the influence of contact time, adsorbent dose, and pH. The results revealed that it is not possible to definitely determine the preference or non-preference of a cation based only on selectivity coefficients. The isotherm experiment showed that the amount of potassium adsorption increased with the increase of the initial equivalent fraction of potassium in the solution. The highest value of R2 and the lowest value of SE were obtained for simple linear and Freundlich equations, respectively

The Level of Environmental Commitment in Tehran Hotels

Nowadays sustainable tourism development is no more considered as a choice but a necessity. In order to achieve sustainable tourism development, all actors in tourism system should undertake the sustainability commitments such as environmental commitment. The purpose of this paper is determining the level of environmental commitment in Tehran accommodation facilities, and identifying the factors that affect the propensity of managers of these units to adopt environmental considerations in this sector of tourism industry. Therefore the exploratory- descriptive research method is employed. Senior managers of 1-5 star hotels comprise the statistical population of this study. In addition to the descriptive statistics methods, various nonparametric inferential statistics tests are applied in analyzing the collected data. Findings of the study manifest that environmental management in the studied hotels can be classified into four levels of environmental commitment with most hotels situating at the basic level of environmental commitment (level 1). Also, according to the research findings “ cost saving” is the most important motivation and “heavy cost of establishing and implementing environmental management practices” is the main obstacle to the implementation of environmental practices. An important finding of this study is that public ownership, size of hotels and the type of their clientele affect achieving more advanced levels of environmental commitment. Environmental Commitment, Hotel, Environmental Management, Impact Factors, Tehra

Synoptic–Dynamic Patterns Affecting Iran’s Autumn Precipitation during ENSO Phase Transitions

We compared the effect on autumn (October, November, December) precipitation over Iran during two types of El Niño–Southern Oscillation (ENSO) phase transitions from the perspective of anomalies in wave activity flux and sea level pressure along the Atlantic–Mediterranean storm track, as well as precipitation. We used Oceanic Niño Index (ONI) to identify the transition phases of ENSO (El Niño to La Niña and also La Niña to El Niño, referred to as type 1 and type 2, respectively). Climate data during the period of 1950 to 2019 used in this study is derived from NCEP-NCAR reanalysis. In order to investigate the intensity and direction of Rossby wave trains in different ENSO transitions, we used the wave activity flux parameter, and to evaluate the statistical significance of values, we calculated Student’s t-test. The impact of the Atlantic storm track on the Mediterranean storm track was shown to be greater in type 2 transitions. Further, the existence of a stronger wave source region in the Mediterranean region during type 2 transitions was established. Results also showed the weakening of the Iceland low and Azores high pressure in type 1 transitions and the reinforcement of both in type 2, with the differences being significant at up to a 99% confidence level. Pressure values over Iran were at or below normal in type 1 years and below normal in type 2. Finally, the composite analysis of precipitation anomaly revealed that during ENSO type 1 transitions, most regions of Iran experienced low precipitation, while in type 2, the precipitation was more than average, statistically significant at 75% confidence level or higher over the northern half of the country