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Soil Test Soils of Different Available Correlation Studies on Some East Pakistan: Comparison of Methods for Measuring Available Soil Phosphorus

A. Islam
Department of Soil Science, Dhaka University, Dhaka, Bangladesh

I. Rashid Chowdhury
Department of Soil Science, Dhaka University, Dhaka, Bangladesh

Abstract/ Executive Summary:

A correlation study was made between the soil phosphorus as measured by three different chemical methods and the phosphorus taken up by soybean plants grown on the soil. Bray No.1 method was found to be comparatively the most accurate of the three methods. The sequence of efficiency of the three methods is as follows: Bray No.1 method> Truog's method> N/2 Acetic acid method. It was, therefore, concluded that Bray No.1 method can be best applied for evaluating available phosphorus for fertilizer recommendation on acid soils of East Pakistan. Soil samples representing 0-6" depth and differing in texture and pH were collected from Cox's Bazar, Dacca University Experiment Station (Tejgaon), Govt. Agricultural Farm (Tejgaon) and Demra (Dacca). Bray No.1 method was found to be comparatively the most accurate of the three methods is as follows: Bray No.1 method> Troug's method> N/2 Acetic Acid method. It was, therefore, concluded that Bray No.1 method can be best applied for evaluating available phosphorus for fertilizer recommendation on acid soils of East Pakistan.

Keywords: Soil, Phosphorus, Chemical methods, Acetic acid method

Location: Cox's Bazar and Dhaka district, Bangladesh

Start Date: 00-00-1963

End Date: 00-00-1963

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

This study was conducted with the objective to evaluate the phosphorus availability in four different soils varying in texture and pH.

Methodology:

Soil samples representing 0-6" depth and differing in texture and pH were collected from Cox's Bazar, Dhaka University Experiment Station (Tejgaon), Govt. Agricultural Farm (Tejgaon) and Demra (Dhaka). A green house experiment was set in the Soil Science Green House of Dhaka University in 1963. Eight pounds of air dried soil, which was screened to pass through two millimeter sieve was taken in each pot (expecting Cox's Bazar, where 3 Ibs. of soil were used due to shortage of soil). The experiment was arranged in a randomized block design with three replications and with six rates of phosphate fertilization (with the exception of Cox's Bazar soil where five rates were used). The treatment one received no fertilizer phosphorus while treatments 2, 3, 4, 5 and 6 were fertilized with phosphoric acid (H₃P0₄) at the rate of 15 Ibs., 30 Ibs., 60 Ibs., 100 Ibs. and 240 Ibs. of elemental phosphorus per acre basis, respectively. The fertilizers were thoroughly mixed with the soil seven days prior to seeding. Inoculated soybean (Var. - K-16) was planted on 21st March 1963. Twenty seeds were sown in each pot (Germination percentage was-55) at a regular distance from each other. Only ten plants in each pot were kept after proper thinning. Plant samples were taken at random from each pot, at two different stages of its growth - early stage when the plants were 5 days old; and pre-flowering stage when the plants were - 65 days old. The plants were cut off at a level one inch above the surface of the soil. About ten grams of soil were also collected carefully from each pot, corresponding to each plant sampling date. The soil samples, obtained from each pot, were air dried, ground and then screened to pass through a two-millimeter sieve. Then they were properly preserved in the bottles for chemical analysis. Plant samples were also dried, weighed, ground and ashed with Mg-acetate and analyzed calorimetrically for phosphorus, as described. Measurements of the available phosphorus in the various soils were obtained in the laboratory by three different methods described in brief as follows: (a) Bray No.1 method which was originally proposed by Bray and Kurtz (1945) and was later modified. The extractant used was 0.03 N NH₄F in 0.025 N HCI. The soil: extractant ratio was 1:50 and the extraction time was five minutes. (b) Troug's method (1930) which was later modified by Peech et. at. (1947) was used. The extractant used was 0.002N H₂S0₄ solution buffered at pH 3.0 with (NH₄)₂S0₄. The soil: solution ratio was 1:100 and extraction period was 30 minutes. (c) Hibbard (1931) 0.5 N CH₃COOH method was used. The soil extractant ratio was 1:100 and extraction time was two hours.

Source of Information: Pak. J. Scientific Res. 19(1): 1-8, 1967

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Achievement/Findings:

Bray No.1 method was found to be comparatively the most accurate of the three methods is as follows: Bray No.1 method> Troug's method> N/2 Acetic Acid method. It was, therefore, concluded that Bray No.1 method can be best applied for evaluating available phosphorus for fertilizer recommendation on acid soils of East Pakistan.

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