B. Kamali; A. Mahdavi; A. Sotoodehnia
Abstract
Introduction: Over application of phosphorous-containing fertilizers is common among the farmers. Excess amounts of phosphorus can potentially cause more phosphorous losses through water flow on the soil surface or leaching into the soil profile. The ability of highly phosphorus-fertilized soils to maintain ...
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Introduction: Over application of phosphorous-containing fertilizers is common among the farmers. Excess amounts of phosphorus can potentially cause more phosphorous losses through water flow on the soil surface or leaching into the soil profile. The ability of highly phosphorus-fertilized soils to maintain excessive amounts of phosphorus and prevent losses largely depends on the phosphorus adsorption capacity of the soil. The purpose of this study was to investigate and compare phosphorous adsorption isotherms in soil samples of four agricultural areas located in Qazvin plain and determine the most appropriate equation to describe the equilibrium adsorption in the studied samples. Identification of the most accurate model of adsorption kinetics using the investigated kinetics equations in one of the soil samples was another objective of this study. The linear regression analysis and correlation between physical and chemical properties of different soils with adsorption coefficients of Langmuir equation was also investigated. Based on mentioned points, the results of this study can help to increase the availability of applied phosphorous for plants, reduce phosphorous losses and proper management of phosphate fertilizers consumption in the study areas.
Materials and Methods: In order to study the soil properties and phosphorous adsorption, soil samples of four villages included Zaaferan (A), Koochar (B), Mehdi Abad (C) and Kamal Abad (D) were taken from 0 to 30 cm depth and stored in plastic bags after air drying. Batch experiments using a standard method recommended by the SERA-IEG17 group were used to determine the amount of phosphorous adsorbed to soil particles. The steps to perform the equilibrium were as follows:
1- Dry soil samples were crushed and passed through a 2 mm sieve.
2- One gram of the soil sample was placed in a 60 ml container.
3- 0.01 M CaCl2 solution was prepared and different concentrations of phosphorous including 0, 5, 10, 15, 20, 30 and 80 mg/l were created by adding certain amounts of KH2PO4 to this solution. 25 ml of these solutions were added to each soli sample to give a 1:25 soil to solution ratio and three drops of chloroform were added to each container to prevent microbial activity.
4- The suspension samples were placed in a shaker machine (250 rpm) at 25°C for 24 hours.
5- Then, the samples were removed from the shaker and allowed to settle for one hour and then passes through a fine filter (Mesh 42).
6- Phosphorous concentration was measured by the molybdate-vanadate method followed by spectrophotometric determination at 470 nm.
7- The amount of phosphorous adsorbed in each soil sample was calculated from the difference of the initial and secondary concentration values.
The adsorption kinetics experiment was similarly performed, with the exception that one soil sample with average adsorption value (sample C) was selected and the phosphorous solution at a concentration of 20 mg/l added to the soil samples. Phosphorous contact times with soil were considered as 0.17, 0.5, 1, 2, 4, 8, 16, 24, 48 and 72 hours. In this study, using CurveExpert 1.4 software and by matching Pseudo-first-order, Pseudo-second-order, Intra-particle diffusion, Kuo and Lotse (1974), Barrow and Shaw (1975) and Panda et al. (1978), equations on the data obtained from kinetics adsorption experiments, and the coefficients were estimated in these equations (adsorption parameters). Furthermore, by calculating the coefficient of determination (R2) of these equations and the standard error of the estimate (s), the most appropriate and accurate model of phosphorous adsorption kinetics for the soil sample was determined. Similarly, from Langmuir, Freundlich, Linear and Van Huay equations, the most appropriate isotherm was determined for estimating phosphorous equilibrium adsorption in the studied areas. Also, correlation and linear regression analysis were performed to determine the relationship between the physical and chemical parameters of the soils and the coefficients of Langmuir isotherm using Minitab software.
Results and Discussion: According to the results, the highest coefficient of determination (R2) and the lowest standard error of the estimate (s) for all four samples were related to Langmuir, Freundlich, Van Huay and Linear equations, respectively. Therefore, in this study, Langmuir isotherm was the most accurate model for estimating equilibrium adsorption of the phosphorus to the soils of the study areas. However, the Freundlich and Van Huay equations also showed a good correlation with the laboratory data. Comparison of the results of various studies in these fields showed that the type of isotherm corresponds to phosphorous adsorption data in each experiment is related to the physical and chemical properties of soil and adsorption sites. The amounts of maximum phosphorous adsorption capacity (qm coefficient in Langmuir equation) for the soil samples A, B, C and D were 0.49, 0.31, 0.42 and 0.4 mg/g, respectively. In kinetic study, Although, Kuo and Lotse, Barrow and Shaw and Panda et al. equations had a coefficient of determination (R2) above 0.95 ; the highest accuracy was related to the Kuo and Lotse equation with R2 of 0.974. The coefficients of this model included k (reaction rate) and m (constant coefficient) were 0.007 l/gr.min and 13.2, respectively. Based on the results of this study and other adsorption studies, soil physical and chemical properties including EC, PH, soil calcium content, clay content and porosity were among the parameters affecting adsorption rate and the type of the most accurate equation of adsorption estimation. Considering the soil properties that were most correlated with adsorption coefficients, it can be concluded that the high percentage of clay and low levels of organic matter and soluble calcium are the main causes of the high phosphorous adsorption in soil. The correlation coefficients (r) of these three soil parameters with the maximum adsorption capacity (qm) were 0.61, -0.97 and -0.92, respectively.
Conclusion: According to the results of this study, Langmuir was the most accurate isotherm model and the soil sample of Zaaferan area has the most adsorption capacity with qm of 0.49 mg/g, which is related to low levels of soil organic matter. Therefore adding organic matter to the soils can be used as a solution to increase cultivated plants access to applied phosphorous and reduce phosphorous adsorption into the soil and thus reduce losses and leaching of excess phosphorous in the profile or soil surface.
hamid reza mehrabadi; Ahmad Nezami; Mohammad Kafi; Malihe Ahmadifard
Abstract
Introduction: More plains of Iran are located in arid and semi-arid regions and so agricultural production systems depend heavily on water. Recently, the reduction of water resources has become a serious threat for crop production such as cotton planting. Therefore, application of low irrigation methods ...
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Introduction: More plains of Iran are located in arid and semi-arid regions and so agricultural production systems depend heavily on water. Recently, the reduction of water resources has become a serious threat for crop production such as cotton planting. Therefore, application of low irrigation methods can be an appropriate method to cope with mentioned condition. In addition, it is vital to identify the cotton cultivars reaction to water deficiency. Sensibility of some cotton cultivars is lower than others. Sensitive cultivars seed cotton yield decreases more than tolerant cotton cultivars. Moreover, some of growth stages in cotton plant are more sensitive to water deficiency stress. For example, flowering stage is more sensitive than vegetative growth stage, and boll number per plant is more effective parameter on yield than boll weight. Ulla and et al (2) showed that there are genetic variations for drought stress toleration in cotton plant. Afshar and Mehrabadi (3) indicated that low irrigation on the basis of 50% and 75% of cotton water requirement had no significant effect on vegetative growth of cotton plant. However, it caused the increase of flower and boll shedding per plant. Application of tolerant cultivars compared with sensitive cultivars can increase seed cotton yield under drought stress condition. Consequently, the aim of this study is to survey yield and related morphological traits reactions in sensitive and tolerant cotton cultivars to different water deficiency levels.
Materials and methods: Two tolerant cotton cultivars (Armagan and Varamin) and two sensitive cotton cultivars (Coker349 and Nazili84) as a subplot at three irrigation levels (as a main plot) using split plot design based on complete block design with three replications were carried out at Agricultural Research Station of Kashmar in 2011. Three levels of water consumption based on Penman-Montith method and using cotton KC coefficients were [33% (I33%), 66% (I66%) and 100% (I100% of water requirement)] that it were take placed using drip irrigation method. Yield and yield components traits such as height, the number of boll per plant, boll weight, flower and boll shedding percent, seed cotton yield, biological yield, earliness percent and harvest index were determined at the end of experiment. Data analysis was carried out using Excel and MSTAT-C software.
Results and Discussion: The results showed that although water deficiency stress decreased vegetative components, the amounts of decreasing were higher in tolerant cultivars than sensitive cultivars but, by contrast, the reproductive components of tolerant cultivars indicated lower decreasing than sensitive cultivars under water deficiency stress. For example, Varamin cotton cultivar had more number of bolls per plant than Coker349 as a sensitive cultivar. The results also showed that more retention of boll number per plant was the main factor of cultivars difference as for seed cotton yield. The highest number of boll and flower per plant retention belonged to sensitive cultivars such as Coker349 and Nazili (71.2 and 69 percent, respectively) at 66 percent of water consumption and the lowest number of boll and flower per plant retention were 92.3 percent belonging to Varamin as a tolerant cotton cultivar at full water irrigation treatment. The results indicated that all yield components except boll weight were significantly affected by low irrigation levels. In addition, the results revealed that low shedding of flower and boll and accordingly more retention of boll number per plant and also biomass preservation under drought stress were the main factor in yield of tolerant cultivars in comparison with sensitive cultivars. Biological yield reduction was higher than seed cotton yield under water stress condition. High and significant correlation was observed among yields with boll number per plant, biological yield and harvest index under drought stress. Moreover, there was a significant correlation between yield with plant height and biological yield only in full irrigated treatment. Furthermore, harvest index decreased significantly under drought stress. Harvest index value for Coker349 was significantly lower than other cultivars. Coefficient correlation between harvest index and yield and its components showed that harvest index was more dependent with seed cotton yield to biological yield. Therefore, tolerant cultivars had higher seed cotton yield and also biological yield in comparison with sensitive cultivars. While there was a significant correlation between yield with plant height and biological yield only in full irrigated treatment.
