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Characterization of Some Representative Calcareous Soils of Bangladesh with Respect to Soil Phosphorus Requirements

Mohammad Z. Afsar
Department of Soil Science, University of Chittagong, Bangladesh.

Mohammad Enayet Hossain
Department of Soil, Water and Environment, University of Dhaka, Bangladesh.

Abstract/ Executive Summary:

Phosphate sorption equations have been widely used to characterize soils with respect to their phosphorus requirements (P_req). For the sorption study, the soils were equilibrated with 0.01 M CaCl₂ solution containing graded concentrations of phosphate (0, 1, 10, 25, 50, 100 and 150 mg P L^-1). The P_req values of four calcareous soils were determined from the Langmuir, Freundlich and Temkin equations. The Langmuir equation was best fitted to the P sorption data. Among the four soil series, the Ghior soil series occupying the lowest position of catena sorbed the highest amount of phosphate. The amounts of sorbed P maintaining 0.2 mg P L^-1 in soil solution ranged from 14.14 to 33.56, 27.99 to 45.80 and 16.16 to 51.72 mg kg^-1 soil which were derived from the respective Langmuir, Freundlich and Temkin equations. P_req values derived from the Freundlich and the Langmuir equations were negatively correlated with Olsen-P content of the soil (r >-0.975, p<0.05). Again, P_req values determined from the Freundlich equation were positively correlated with percent clay content (r >0.901, p<0.05) of the soil. Phosphate was sorbed by the soils in the following order: Ghior>Ishurdi>Gopalpur>Sara soil series. However, based on their P_req values, the soils can be arranged in the following order: Ishurdi>Ghior>Gopalpur>Sara soil series. To maintain a desired P concentration in the soil solution, the Ishurdi soil will be required to supply more P than others.

Keywords: Calcareous soil, Soil phosphorus requirement, Phosphate sorption, Sorption maximum

Location: Department of Soil Science, University of Chittagong.

Start Date: 00-00-2006

End Date: 00-00-2006

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

1. To describe some calcareous soils of Bangladesh in terms of their phosphorus requirements

2. To determine the relationships between easily measurable soil characteristics and soil phosphorus requirements.

Methodology:

The experiment was carried out in the laboratory of the Department of Soil Science, University of Chittagong with four different benchmark calcareous soils of Bangladesh, namely the Sara (Calcaric Fluvisol), the Gopalpur (Calcaric Fluvisol), the Ishurdi (Calcaric Fluvisol) and the Ghior (Calcaric Fluvisol) soil series. The soils are grouped according to the World reference base for soil resources 2006. Soils used in the investigation belong to the Ganges River Floodplain Alluvium. The soils under study were part of a catena. The Sara soil series occupied the higher and the Ghior soil series occupied the lower position of the catena. Soil samples at a depth of 0-15 cm were collected from 20 spots from a square area of ~1 km² under a soil series. Approximately equal amounts (on weight basis) of these samples were mixed together to form a composite sample. The soils were then air dried at room temperature (25±2°C) for 7 days, ground and passed through a 2 mm sieve. Soil samples were analyzed for textural classes, pH, total P, Olsen-P, organic matter and free carbonate content. Particle size analysis was done by hydrometer method. Soil organic matter, pH and total P contents were determined by following standard methods. Available P was extracted by 0.5 M NaHCO₃ at pH 8.5 and P in the extract was determined by ascorbic acid blue color method. Each analysis was replicated thrice. One gram soil sample was equilibrated in a 50 mL centrifuge tube with 20 mL 0.01 M CaCl₂ solution containing 0, 1, 10, 25, 50, 100 and 150 mg P L^-1(equivalent to 0, 20, 200, 500, 1000, 2000 and 3000 mg P kg^-1 soil) as KH₂PO₄. The soil samples were then incubated at room temperature (25±2°C) for 3 days. After centrifugation at 4500 rpm for 15 minutes, the mixtures were filtered through Whatman No. 42 filter paper and the amount of P sorbed by the soils was calculated from the difference between the concentration of soluble P added in the initial solution and the concentration of P in the solution at equilibrium. The P content of the supernatant solution was measured employing ascorbic acid blue color method by a T80/T80+UV-Vis Spectrophotometer at wavelength of 882 nm. The sorption values of each soil were fitted according to the Langmuir, Freundlich and Temkin equations. The incubation experiment was arranged in the laboratory according to completely randomized design. Regression curve fitting equations were drawn by the Microsoft Office Excel program. Suitability of different adsorption equations were studied by calculating the R² values of the respective equations. Correlation coefficients were calculated among soil P_req values and soil properties, namely percent clay, organic matter and Olsen-P content of the soil. Microsoft Office Excel and SPSS-16 computer programs were used to estimate relationships between phosphate sorption and different soil properties.

Source of Information: International Journal of Agricultural Research, 7(8): 388-397, 2012, ISSN 1816-4897.

Article Link (Online Journal): DOI: 10.3923/ijar.2012.388.397; URL: http://scialert.net/abstract/?doi=ijar.2012.388.397

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Results from this sorption study showed that the calcareous soils varied considerably in their phosphate retention capacities. Considerable variations were also observed in P requirements (P_req) values, i.e., the amount of P that a soil contains when a particular P level exists in solution. P_req values determined from the Langmuir and the Freundlich equations were highly correlated with percent clay and Olsen-P content of the soil. Among the four soil series, the Ishurdi soil requires more P fertilization than others to maintain a desired solution P concentration. However, relationships determined in this study are needed to be verified across a wide range of soils. These relationships could be readily integrated into existing management practices for improving soil fertility and safeguarding water quality.

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