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Extractable Phosphorus Contents of Some Soils of Bangladesh and Their Correlation with Phosphorus Concentration in Rice Leaves

Enamul Haque
Department of Soil Science, University of Chittagong, Chittagong, Bangladesh.

Abul Kashem*
Department of Soil Science, University of Chittagong, Chittagong, Bangladesh.

Khan Towhid Osman
Department of Soil Science, University of Chittagong, Chittagong, Bangladesh.

Abstract/ Executive Summary:

To observe the availability of phosphorus by different extraction methods in some cultivated soils of Hathazari Upazilla of Chittagong District, this study was carried out with 36 surface soil samples (0 - 15 cm) belonging to six soil series, namely Bijipur, Pahartali, Mirsarai, Manu, Raojan and Noapara. Physical and chemical characteristics of the soils were also determined with an objective of identifying the soil factor(s) regulating P extractability. Three P extraction methods, namely Olsen (0.5 M NaHCO3, pH 8.5), Mehlich-3 (0.2 N CH3COOH + 0.013 N HNO3 + 0.015 N NH4F + 0.25 N NH4 NO3 + 0.001 M EDTA) and Bray & Kurtz-1 (0.03 N NH4F + 0.025 N HCl) were used. There was a wide variation in the extractability of P ranging from low to high categories. Olsen method extracted the largest amount of P (2.07 - 45.36 mg kg−1) while Bray & Kurtz-1 extracted the smallest amount (1.02 - 21.79 mg·kg⁻¹). The mean extractable P in soils was found to be in the order of Olsen > Mehlich-3 > Bray & Kurtz-1. Soil pH was the most dominant factor in deter-mining P extractability. Available P was negatively correlated with percentage of clay, organic carbon and CEC and positively correlated with pH. Although the three methods extracted different amounts of P from soil, values of P extracted by the different methods were strongly correlated among themselves and with the leaf phosphorus concentration of rice growing in these soils.

Keywords: Soil Series; Available P; Olsen P; Mehlich-3 P; Bray & Kurtz-1 P

Location: Hathazari Upazilla of Chittagong District

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Fertilizer

Objectives:

In the present study, available P content of soils of 36 rice fields belonging to six soil series were determined by three methods including Bray and Kurtz-1, Mehlich-3 and Olsen methods, and their values were correlated with leaf P concentration of rice growing in farmers field.

Methodology:

Collection of Soil Samples Six soil series namely Bijipur, Pahartali, Mirsarai, Manu, Raojan and Noapara were selected on the basis of their land types, drainage, textures and parent materials and covering major soils of the Hathazari Upazilla of Chittagong. Multiple soil samples from each soil series were collected for evaluating the P availability status. Characteristics of these soil series have been defined by the Soil Resources Development Institute of Bangladesh. The soils were silty clay to sandy loam and within the same soil order Inceptisols. Soil Analysis Collected soil samples were air dried, ground and sieved through a 2 mm sieve. Soil samples were dried in an oven at 105 ⁰C for 48 hours before analysis. Particle size analysis was made by hydrometer method described by Day. Soil pH was measured by corning (Model-7) glass electrode pH meter from soil water suspension at the ratio of 1:2.5. Soil organic carbon was determined by Walkley and Black’s wet oxidation method. Cation exchange capacity was determined by using 1N NH4OAC solution at pH 7.0. Available phosphorus of soil was extracted with three different extractants. To measure Mehlich-3 and Bray & Kurtz-1 extractable P, 2 g soil was extracted with 20 ml of Meh-lich-3 extractant (0.2 N CH3COOH + 0.013 N HNO3 + 0.015 N NH4F + 0.25 N NH4 NO3 + 0.001 M EDTA) and with 20 ml of Bray & Kurtz-1 extractant (0.03 N NH4F + 0.025 N HCl), respectively after 5 minutes shaking at room temperature. In the case of Olsen P, 1 g soil was extracted with 20 ml of 0.5 M NaHCO3, pH 8.5 at 30 minutes shaking time. Phosphorus in the soil extracts was determined spectrophotometrically by the ascorbic acid blue color method. Statistical analyses were done by using Minitab program. Leaf Analysis Mature leaves of rice (Oryza sativa) growing in farmers fields during the time of soil sampling were collected, dried in the laboratory, ground and digested in conc. H2SO4 + H2O2 + LiSO4 digestion mixture and analyzed for N, P and K. Nitrogen in extract was determined by micro-Kjehdahl distillation, P by vanadomolybdate yellow colour in spectrophotometer and K in an atomic absorption spectrophotometer. Soil test P values were correlated (Pearson’s simple linear correlation) with leaf P values.

Source of Information: Open Journal of Soil Science Vol.3 No.2 (2013), Article ID:32587,8 pages

Article Link (Online Journal): DOI:10.4236/ojss.2013.32013

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Extractable P in the present study varied considerably with the kind of extractants and the type of soils. Among the three extractants used (Olsen, Mehlich-3 and Bray & Kurtz-1), Olsen extractant, i.e. 0.5 M sodium bicarbonate extracted greatest amount of available P and Bray & Kurtz-1 extractant, i.e. 0.03 N ammonium fluoride and 0.025 N hydrochloric acid extracted the least. As phosphorus values extracted by the three methods were highly correlated among themselves and with the leaf phosphorus values, it may be concluded that any of the methods used in the present study is suitable for testing soil P.

Knowledge Management: Journal