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Phosphorus Sorption as Influenced by Soil Characteristics on Four Ganges Tidal Floodplain Soils of Bangladesh.

Dr. Md. Fazlul Hoque
Professor
Department of Soil Science, Patuakhali Science and Technology University, Patuakhali-8602, Bangladesh

Abstract/ Executive Summary:

A laboratory experiment was conducted at the Department of Soil Science, Patuakhali Science and Technology University during 2008 to determine the effect of soil characteristics (clay content, pH, organic matter content and available P) on phosphorus (P) sorption for 4 Ganges Tidal Floodplain soils of Bangladesh. Phosphorus sorption increases with increases of clay content, organic carbon content but decreases with increases of soil pH. Amount of phosphorus sorption capacity in different studied soils varied from 531.81 to 565.29 mg kg^-1. The maximum P adsorption capacity ranged from 1429 to 1667 mg kg^-1 and correlated with organic carbon (r = 0.80, P>0.05). The calculated energy of P adsorption of the soils ranged from 0.54 to 2.00 mg L^-1 and correlated with organic carbon (r = 0.81, P>0.05). Buffering capacity ranged from 0.29 to 0.48 and correlated with pH_H2O (r = 0.93, P>0.01), pH_KCl (r = 0.81, P>0.05), there was apparently negative correlation between the organic carbon (r = -0.87, P>0.05), maximum adsorption capacity (r = -0.86, P>0.05) and energy of adsorption (r = -0.89, P>0.05). Conventional adsorption equation, such as the Langmuir, Freudlich and Temkin equations satisfactorily described the P sorption of the soils. It was found that all equations were fitted well (r² value 0.84, 0.89, 0.94, 0.93 for Langmuir; 0.98, 0.98, 0.93, 0.98 for Freudlich and 0.72, 0.78, 0.81, 0.80 for Temkin equations) for the studied soils.

Keywords: Adsorption capacity, Buffering capacity, Freudlich, Langmuir, Phosphorus sorption

Location: Department of Soil Science, Patuakhali Science and Technology University

Start Date: 00-01-2008

End Date: 00-04-2008

Program Area: Crop-Soil-Water Management

Commodity: Fertilizer

Objectives:

To determine and evaluate P sorption in relation to soil properties in Tidal Floodplain soils of Bangladesh.

Methodology:

The soil samples were collected from farmer’s field of Amtali and Kalapara upazilla of greater Patuakhali district under Ganges Tidal Floodplain region of Bangladesh. The soil samples were taken from surface (0-15 cm depth).Sampling sites were selected on the basis of low pH, phosphorus deficiency, medium high land, light textured (silty clay and clayey), rice-rice phosphate fixing problem areas of Bangladesh. Soils were sampled in winter 2008 after T. Aman harvest. The collected soil samples were air-dried and ground to pass through a 2-mm sieve and then mixed to form a composite sample.Soils were analyzed in Soil Science laboratory and Central laboratory of Patuakhali Science and Technology University during January 2008 to April 2008. The sand, silt and clay content of soils were determined using the hydrometer method (Black et al., 1965). Soil pH_H2O was measured in a 1:2.5 soil water ratio, using glass electrode pH meter method (Jackson, 1958), and the pH_KCl was also measured by using a 1.0 M KCl in a similar manner as in pH_H2O determination. Organic carbon of soil was determined by Walkley and Black wet digestion method as outlined by Nelson and Sommers (1982). Available phosphorus was determined by Olsen and Bray method. Available Fe was determined by Sodium dithionate-citrate system buffered with sodium bicarbonate (Mehra and Jackson, 1960). Available S was determined by calcium chloride (0.15%) as outlined by Black (1965). Phosphorus sorption isotherms were constructed using the standardized phosphorus adsorption isotherm procedure (Nair et al., 1984). After equilibration, the supernatant was passed through a Whatman # 42 filter paper and the filtrate was analyzed for P following Murphy and Riley (1962) method.

The equilibrium P concentration data were interpreted following Langmuir, Freundlich and Temkin Equations as described below:

Langmuir equation

The Langmuir adsorption equation is given by:

C/(x/m) = 1/kb +C/b (1)

All measurements of P were done in duplicate.

Source of Information: J. Patuakhali Sci. and Tech. Univ. 2010, 2(1):1-11

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Maximum adsorption capacity, energy of adsorption and buffering capacity were not correlated with soil properties (sand, silt and clay content) but they were correlated (P>0.05) with organic carbon content. Buffering capacity was well correlated with pH_H2O(P>0.05) and pH_KCl (P>0.01). The maximum P sorption capacity varied from 1429 µg g^-1 to 1667 µg g^-1 and the P buffering capacity of the soils varied from 162 to 195. Similarly, the variation in the P adsorption energy of the soils ranged from 0.54 to 2.00 g mL^-1. The fixed P will be solubilized due to the application of manure and non-acid forming fertilizer. In future the sorbed P will be dissolved due to the rhizospheric influences and the action of different organic acids produced during organic matter decomposition. The soils that showed lower P buffering capacities may need more frequent application of P fertilizer than soils with relatively higher buffering capacities. P sorption capacity of soil is a key factor in P cycling, knowing this parameter is a prerequisite for sustainable cultivation and we need in-depth future research on P chemistry and P fertility.

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