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Speciation of Inorganic Phosphorus in Some Bench-merk Soils of Bangladesh

P. Chowdhury
Department of soil, water and Environment, University of Dhaka, Dhaka-1000, Bangladesh

S. Hoque
Department of soil, water and Environment, University of Dhaka, Dhaka-1000, Bangladesh

A. Parvin
Soil and Environment Section, Biological Research Division, BCSIR Laboratories, Dhaka, Bangladesh

M. Moniruzzaman
Soil and Environment Section, Biological Research Division, BCSIR Laboratories, Dhaka, Bangladesh

Abstract/ Executive Summary:

To study the phosphorus transformation in soils, experiment was conducted in the laboratory. In this study, three different bench-mark soil series of three different Agro-ecological Zones namely, Brahmaputra (Jamuna) floodplains (Dhamrai series, Areni-Eutric gleysols), Low Ganges River Floodplain (Ishurdi series, Chromi-calcaric Gleysols), and Madhupur Tract (Tejgaon series, Chromi-Calcaric Gleysols ) of Bangladesh were selected. For conducting this experiment, all the determination was performed triplicate. The changes of phosphorus fractions were discussed. Soil Phosphorus pools were assessed by sequential P fractionation on days 0, 7, 20 and 40. The inter conversions of different P- fractions were noticed during the course of incubation experiment. The magnitude of these changes differed among soils, being greatest in the Dhamrai soil. Principal component analysis of the data showed that the size of the P pools was related to soil properties; high concentrations of Ca-P were associated with high pH and calcium concentrations, high concentrations of Fe-P and residual P were correlated with high aluminium. It can be concluded that soil P pools can be generalized across the three soil used in this study, but that the size of the P pools is affected by soil properties.

Keywords: Speciation; Inorganic pohosphorus, Bench-merk

Location: Dhamrai, Ishurdi and Tejgaon series of soil

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

To have a comprehensive understanding of soil properties interactions such as pH with changes in P status using conceptual P pools of soils of Dhamrai, Ishurdi and Tejgaon series.

Methodology:

Experimental setup The surface soil samples (0 - 15 cm) were collected from Dhamrai, Ishurdi and Tejgaon series. The soils were air-dried and ground to pass through a 2 mm sieve. The ground samples were preserved for analyses. Measurements of selected physical and chemical properties of the soils were carried out in triplicate according to conventional methods. Before the experiment, an incubation study at a temperature of 24°C ± 2°C was carried out in the laboratory. Ten gram soil was taken in a 50 ml beaker. Beakers were covered by Available parafilm to maintain moisture at ?eld condition. Soil samples after 0, 7, 20 and 40 days of incubation were placed in centrifuge tubes. These soils were analyzed for fractionation of inorganic P fractions following Chang and Jackson (1957). Analyses Particle size analysis of the soil samples was done by hydrometer method as described by Gee and Bauder (1986). Textural classes were determined by Marshall's Triangular co-ordinate system. Soil pH was measured (?eld condition) electrochemically by using glass electrode pH meter and the ratio of soil to water was 1:2.5 (Jackson 1973). Cation exchange capacity (CEC) of soils was determined using neutral 1 N NH₄OAc solution as described by Schollenberger and Simon (1945). The organic carbon of the soil samples was determined by wet - oxidation method as outlined by Walkley and Black (1934). Soil organic matter was calculated by multiplying the percent value of organic carbon by the conversion factor of 1.724. Total nitrogen was determined by micro Kjeldahl's method as described by Jackson (1973). Soil samples were digested with HNO₃ - HC1O₄ (2:1) mixture as described by Piper (1950) for the determination of total P, K and S. Total acid digested potassium was determined by using Flame Photometer (Model: Jenway, PFP7) at 769 nm wavelength. Total Phosphorus was determined by vanadomolybdate yellow color method using UV-Visible Spectrophotometer (Model: Analytik jena Specord 205) as described by Jackson (1973). Total sulfur was determined by turbidimetric method (Hunt, 1980). The concentrations of various P pools were determined by sequential P fractionation (Chang and Jackson, 1957) with some modifications. 25 ml 1M NH₄Cl was added in 0.5 gm soil sample in 50 ml centrifuge tubes, shaked 30 min, centrifuged and collected supernatant. Then 25 ml 0.5M NH₄F (pH 8.2) was added to the residue, shaked 1 h, centrifuged, collected supernatant, washed twice with 12-15 ml saturated NaCl and combined the washings to the extract. After that, 25 ml of 0.1M NaOH was added to the soil residue and shaked for 17 h. Then the suspension was centrifuged and decanted the surpantant. Approximately 25 ml of 0.5 N H₂SO₄ was added to the soil residue and shaked for 1 h. Then it was centrifuged for 10 min and decanted the supernatant. The soil was washed twice with 12.5 ml saturated NaCl, and centrifuged. The washings was combined with the extract. Then 20 ml of 0.3 M sodium citrate and 0.5 g of Na₂S₂O₄ was added, stired rapidly and shaked for 5 minutes. The suspension was heated in a water bath at 75°C to 80°C with constant shaking for 15 minutes and centrifuged. The supernatant solution was collected in 50 ml volumetric flask and diluted to 50 ml with deionized water. The soil was washed twice with 12-15 ml saturated NaCl and centrifuged. After that, 25 ml of 0.1M NaOH was added to the soil residue and shaked for 17 h. The suspension was centrifuged and decanted the supernatant. Again, the soil was washed twice with 12-15 ml NaCl and combined with extract. Inorganic phosphorus was determined by ascorbic acid blue colour method of Murphy and Riley (1962).

Source of Information: Bangladesh J. Sci. Ind. Res. 53(1), 7-12, 2018 Received: 31 July 2017;

Article Link (Online Journal): DOI: http://dx.doi.org/10.3329/bjsir.v53i1.35904

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

It may be concluded from the results of the incubation experiment that phosphorus was converted mainly to ES - P, Ca - P, Al - P and Fe - P with time. These fractions rearranged among themselves depending on the nature of the soils during this time. Iron - P is the dominant fraction in Tejgaon soil (pH 4.99) and Ca - P is the major fraction in Dhamrai (pH 6.1) and Ishurdi (pH 8.13) soils. Available P, extracted by Chang and Jackson methods, were significant and higher values were obtained with corresponding incubation periods.

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