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Distribution of Inorganic Phosphates in Some Soils of East Pakistan

A. ISLAM
Department of Soil Science, Dacca University.

T. H. KHAN
Department of Soil Science, Dacca University.

Abstract/ Executive Summary:

The objective of the study was to study the distribution of inorganic phosphates in some soils of East Pakistan. Soil samples representing 0"-6" depth and differing in pH, mechanical and chemical compositions were collected from Savar (Dacca), Pak Tobacco Experiment Station (Rangpur), Benerpota Farm (Khulna), Amritapur (ComilIa) and Madaripur. Each sample was then analysed for the different inorganic phosphates following the fractionation procedure. NH₄CI-soluble phosphates constituted 0 to 1.0%, aluminium phosphate 3.6 to 28.9%, iron phosphate 4.8 to 25.8%, calcium phosphate 18.6 to 77.8% and occluded phosphates 7.9 to 37.8% of the total inorganic phosphates of the soils. Among the various inorganic phosphates, iron and aluminium phosphates were dominant forms in the acid soils of Savar and Rangpur, while in the alkaline soils of Benerpota, Amritapur and Madaripur, calcium phosphate was the dominant form. The highest percentage of occluded phosphate was recorded in Savar clay which belonged to the moderately weathered lateritic soil of Madhupur Jungle Tract.

Keywords: Inorganic phosphates, Soils, East Pakistan

Location: Department of Soil Science, Dacca University

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Fertilizer

Objectives:

An experiment was performed to study the distribution of inorganic phosphates in some soils of East Pakistan.

Methodology:

Soil samples representing 0"-6" depth and differing in pH, mechanical and chemical compositions were collected from Savar (Dacca), Pak Tobacco Experiment Station (Rangpur), Benerpota Farm (Khulna), Amritapur (ComilIa) and Madaripur. Each sample was then analysed for the different inorganic phosphates following the fractionation procedure originally proposed by Chang and Jackson (1957) and subsequently modified by Chang and Liaw (1962). The methods adopted for the mechanical and chemical analysis of soils are as follows: (a) Mechanical analysis- The mechanical analysis was carried out by hydrometer method as described by Piper (1951) and textural classes were determined from the triangular co-ordinates as devised by U.S. Department of Agriculture (1951). (b) pH was determined by glass-electrode. The soil: water ratio was 2:5. (c) Organic carbon was determined volumetrically by wet-oxidation method of Walkley and Black, (1934). (d) Determination of total iron was carried out colorimetrically on an aliquot out of the HCI extract of the Na₂CO₃-fusate of the soil (Jackson, 1962). (e) Total AI was obtained by subtracting iron and titanium (Fe+Ti) from iron, aluminium and titanium (Fe+Al+ Ti) determined gravimetrically by precipitating as hydroxides (Piper, 1951). (f) Total calcium contents of the soils were determined on an aliquot of Na₂C0₃ fusate of the soils by E.D.T.A. method as described by Betz and Noll (1950). (g) Free iron oxide was determined by Karim's (1953) nascent hydrogen reduction method. (h) Free alumina was determined by alizarin (0.5% solution) adsorption on an ignite mass of soil and subsequently abstracting the adsorbed alizarin by sodium oxalate buffered at pH 3.5 with oxalic acid and comparing this abstracted yellow solution with a standard solution of alizarin (quoted from Karim and Sultan, 1961). (i) Free CaC0₃ was determined by extracting the soil with dil. HCI as outlined by Piper (1951).

Source of Information: Pak. J. Biol. & Ag. Sc. Vol. 10. No. 1. 1967

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Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Among the various inorganic phosphates, iron and aluminium phosphates were dominant forms in the acid soils of Savar and Rangpur, while in the alkaline soils of Benerpota, Amritapur and Madaripur, calcium phosphate was the dominant form. The highest percentage of occluded phosphate was recorded in Savar clay which belonged to the moderately weathered lateritic soil of Madhupur Jungle Tract.

Knowledge Management: Journal