azadeh ehsaninezhad; ali abbaspour; hamidreza asghari; hamidreza samadlouie
Abstract
Introduction: Phosphor (P) is the second nutrient element after nitrogen mostly required by plant. P is the main component of nucleic acid, phospholipid, ATP and some coenzymes. The effectiveness of phosphate fertilizer application is only about 15% - 20% and 10 – 25%, based on the different references.Rock ...
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Introduction: Phosphor (P) is the second nutrient element after nitrogen mostly required by plant. P is the main component of nucleic acid, phospholipid, ATP and some coenzymes. The effectiveness of phosphate fertilizer application is only about 15% - 20% and 10 – 25%, based on the different references.Rock phosphate (RP) as a source of P is not expensive, but its availability of P is low. Solubility of RP can be increased by phosphate solubilizing microorganisms. Increasing RP solubility by microorganisms is due to the lowering of pH and/or organic acid excretion. Fungi have been reported to possess greater ability to solubilize insoluble phosphates than bacteria. Among the fungal genera with the phosphate solubilization ability, there are Aspergillus and Penicillium. Aspergillus Niger convert insoluble phosphates into soluble forms through the processes of acidification, production of organic acids, production of acid and alkaline phosphatases, and the release of H+ .These organic acids can either dissolve phosphates as a result of anion exchange or can chelate Ca, Fe or Al ions associated with the phosphates. The aim of this study was to investigate the effect of Aspergillus Niger and green manure on soil P solubility in the incubation conditions.
Materials and Methods: To investigate the effect of Aspergillus Niger and green manure on soil phosphorus availability, an experiment in a completely randomized design with three replications was conducted. The treatments were applied over a period of 70 days and were repeated at 3 incubations. The treatments were included C: control (50 g soil), As: Aspergillus Niger (50 ml/ kg), A: Green manure (1% weight of the soil), S: Sucrose (1 g/kg soil), P: Rock phosphate (150 kg/ha), As + A: Aspergillus niger + Green manure, As + S: Aspergillus Niger + Sucrose, As+P: Aspergillus niger + Rock phosphate, As + S + P: Aspergillus niger + Sucrose+ Rock phosphate , and As + A + P Aspergillus niger+ Green manure +Rock phosphate . Soils were air-dried and crushed to pass through a 2-mm sieve. Treatments were then applied to 50 g of soil and the treated samples were moistened to the field capacity (FC). The moisture of containers was kept near FC soil moisture content throughout the experiment by periodically weighing and replenishing evaporated water. At intervals of 7, 21, 35, 51 and 70 days, the samples were taken and after air drying, pH, EC, available soil phosphorus by Olsen method and soluble phosphorus were measured. The statistical analysis of all data obtained from the experiments was performed using the MSTAT-C software. The mean comparison was performed using Least Significant Difference (LSD) test at 5% level and drawing graphs using Excel software.
Results and Discussion: The results showed that all treatments had a significant effect on the measured parameters at 1% probability level. The effect of treatments and incubation Times on soil pH showed that all treatments were able to reduce soil pH. The greatest decrease was observed in Aspergillus Niger + Green manure (As + A) treatment that could reduce the pH by 0.59 unit. Usually, green manure decreases soil pH through decomposition and release carbon dioxide and organic acids. Aspergillus Niger also reduces pH and thus increases the solubility of soil phosphorus through the production of the metabolites and organic acids and microbial respiration. The effects of the treatments and incubation time on soil electrical conductivity showed that all treatments were able to increase soil electrical conductivity. Most of this increase was related to Aspergillus Niger+ Rock phosphate+ Green manure (As +P+ A) treatment .This increase was probably due to inorganic compounds found in green manure. The effects of the treatments and incubation time on soil available phosphorus and solube phosphorus showed that all treatments were able to increase them. Most of the soluble and available phosphorus amounts were observed in As +P+ A treatment and the amounts of increase resulting from this treatment for soluble and available phosphorus were 0/28 mg/l and 10/79 mg/kg, respectively. However, the green manure treatments and aspergillus alone increased soil soluble phosphorus, but with treatment of Aspergillus Niger (As) in green manure (A) observed that the amount of phosphorus in the soil solution was further enhanced. Organic acids resulting from the decomposition of organic matter by adsorption onto calcium phosphate surfaces and occupy the active sites such as nuclei for the formation of these deposits, prevent the growth of new crystals. These organic acids, in addition to the creation of the complex with calcium cations, reduce the activity.
Conclusions: The results of this study showed that use of phosphate solubilizing microorganisms and organic matter led to the significant decrease in pH and increase in electrical conductivity, dissolved phosphorus and available phosphorus in soil.. However, to obtain more accurate results, it is better to do a pot experiment as well.
M. Saadatpour Mogaddam; A. Abbaspour; Sh. Shavsavani
Abstract
Introduction: Redox potential is one of the most important factors affecting on the solubility of iron minerals in soil. Decreasing redox potential in soil reduces Fe3+ to Fe2+, thereby affecting on solubility of Fe minerals. Application of organic matter to soil under waterlogging condition, decrease ...
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Introduction: Redox potential is one of the most important factors affecting on the solubility of iron minerals in soil. Decreasing redox potential in soil reduces Fe3+ to Fe2+, thereby affecting on solubility of Fe minerals. Application of organic matter to soil under waterlogging condition, decrease redox potential and as a consequence, accelerate the transformation of Fe minerals. The objectives of this study were: 1- The effect of waterlogging on the soluble total Fe concentration and transformation of Fe minerals in different soil pH values. 2- The indirect effects of organic matter on solubility of Fe minerals by changing the redox potential of the soils.
Materials and Methods: A study was conducted to determine the effects of redox potential on solubility of Fe and transformation of Fe minerals during the time. Four agricultural soils were selected from different regions of Iran. The soil samples were treated with 0 (C)and 2% (O) alfalfa powder and then incubated for 12 weeks under 60% Field capacity (F) and waterlogged conditions (S). Subsamples were taken after 1and 12 weeks of incubation and the redox potential, pH value, electrical conductivity (EC), soluble cations (such as Ca2+, Mg2+, K+ and Na+) and anions (such as Cl-, SO42-, PO43- and NO3- ) and soluble Fe concentrations in the subsamples were measured. Concentrations of Fe2+ and Fe3+ species in soil solution were also predicted using Visual MINTEQ speciation program. Mineralogical transformation of Fe minerals was also determined by X-ray diffraction (XRD) technique.
Results and Discussion: The results in 60% Field capacity condition showed that pH value by organic matter (alfalfa powder) application (OF) increased significantly (p≤ 0.05) in acid and neutral soils and decreased in calcareous soils when compared to the control (CF). Organic matter is usually capable of lowering pH of alkaline soils by releasing hydrogen ions associated with organic anions or by nitrification in an open system. On the other hand, it may cause pH to increase in the acid soils either by mineralization of organic acids to carbon dioxide (CO2) and water (thereby removing H+) or by the alkaline nature of the organic residues. This treatment increased soluble total Fe concentration in all soils. It is clear that decomposition of organic matter cause to produce soluble organic compounds and form soluble complexes with Fe, thereby increasing soluble total Fe concentration. Waterlogging (CS) decreased redox potential of the soils gradually with the incubation time, especially in the neutral soil and alfalfa powder application (OS) accelerated this decreasing redox potential. The decrease rates by waterlogging in acid, neutral and two calcareous soils were 2, 3.6, 1.5 and 1.7folds, respectively compared to the control. The soluble total Fe concentration in CS compared to CF treatment increased significantly (p≤ 0.05) in all soils except in acid soil. This increasing was continued with time in all soils except in neutral soil. An important point that OS compared to CS treatment enhanced the soluble total Fe in acid and neutral soils, whereas decreased it in both calcareous soils. However, soluble total Fe increased during the incubation time in all soils except in neutral soil. The increase rates in week 12 relative to week 1were 3.4, 2.2 and 1.8 folds in acid and two calcareous soils, respectively. The decrease of soluble total Fe in the neutral soil is probably attributed to more severe decrease of redox potential in the soil when compared to the other soils. The solubility diagrams and X-ray diffraction results confirmed the formation of pyrite in the acid and neutral soils and the formation of siderite in one of the calcareous soils.
Conclusion: In aerobic condition, organic matter application increased the concentration of soluble total Fe and changed Fe-controlling mineral from soil-Fe to amorphous Fe. Waterlogging decreased redox potential and Fe-controlling mineral changed to pyrite and/or siderite, depending on CO2 pressure and pH value of the soils. It might be pointed out that severe reduction of the redox potential decreases soluble Fe through the formation of insoluble Fe minerals such as Fe sulfides. It is concluded that waterlogging soils can provide available Fe to the plant, though severe decrease of redox potential, by application of organic mater, may decrease Fe availability.
