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Use of 8(oh) Quinoline and Selenious Acid in Determining Available Phosphorus

M. O. Ghani
Dhaka University, Dhaka

A. Islam
Dhaka University, Dhaka

Abstract/ Executive Summary:

The us of 8(OH)Q, as suggested by Ghani, and of Se/A, as suggested by Cooke, in the determination of chemically available- phosphorus were critically investigated with reference to some lateritic soils of high-fixing capacity. Troug's method and the acetic acid method were included in the study for comparison. A combination of the two was also investigated. The order of the fixing capacity of the four oxides as: Fe₂0₃) > AI₂0₃) > Mn0₂> Ti0₂. Se/A yielded better results than 8(OH)Q except with AI₂0₃), her 8(OH)Q gave slightly better results. Successive treatments with Se/A + 8(OH)Q proved more effective in preventing fixation than did the individual treatments. Fixation by F₂0₃) and Al₂O₃) as reduced to practically nil and that by Ti0₂ and Mn0₂ to some extent. To prevent fixation of phosphorus completely during acid extraction, a combination of the two regents appears to b advisable. Both Se/A and 8(OH)Q reduced phosphate fixation in all the lateritic soils studied, but the percentage reduction by 8(OH)Q in all cases except one as only 4-6 pr cent less than that due to Se/A. The combination treatments reduced the percentage fixation still further and to a very low level. The order of efficiency of the methods in extracting chemically available phosphorus is as follows: 8(OH)Q+Se/A; Se/a; 8(OH)Q; Troug's method; and Ac/A. The available phosphorus determined by Se/A and S/A+8(OH)Q methods in different soils show the same relative trend. Use of 8(OH)Q+ Se/A in Ac/A is suggested as the method that will yield the most satisfactory results for chemically available phosphorus.

Keywords: Soil, Nutrient absorption, Plant, Phosphorus

Location: Dhaka University, Bangladesh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

To involve the mechanism of nutrient absorption by the plant from the soil;
To certain factors inherent in the soil itself which operate against the extraction of all the phosphorus soluble in the extractant, or the so-called chemically available phosphorus.

Methodology:

In the present work Cooke's comparison (1) of the use of 8(OH)Q, as suggested by Ghani, and of selenious acid (Se/A), as suggested by Cooke, in the determination of available phosphorus was critically investigated with reference to some lateritic soils of high fixing capacity. Troug's method (4) and the conventional Ae/A method were also compared, and a combination of 8(OH)Q and Sc/A was tried. Oxides of Fe, AI, Mn, and Ti are commonly present in soil and are likely to precipitate phosphate in acid solution. The effectiveness of the reagents under study in preventing phosphate fixation caused by these oxides was investigated. Since Se/a and 8(OH)Q might have preferential action on different oxides, it was throught desirable to determine if better results could be obtained by repeated treatment of the materials with the two reagents. In the fixation study a suspension of the oxide (0.05 g.) was shaken for 2 hours with the reagent dissolved in 195 ml. 0.5 N Ac/A. in the case of Se/A the pH was adjusted to 2.5, and in that of 8(OH)Q to 5.0 by adding NH₄0H (Cooke showed that Se/A is most effective at pH 5). To this suspension 5 ml, of KH₂P0₄ solution containing 0.1 mg. P₂0₅ per ml. was subsequently added. The suspension was shaken for 2 hours more and filtered; the phosphate remaining in the solution was determined. In determining the effect of combined treatment, the same amount of oxide was first shaken with 200 ml. of 0.5N Ac/A containing 0.5 per cent Se/A at pH 2.5. The suspension was filtered and the residue was washed free of Se/S with 0.5N Ac/A. It was then used as before for a fixation study with 8(OH)Q. Fe₂0₃> AI₂0₃ >Mn0₂> Ti0₂both Se/A and 8(OH)Q considerably reduced the phosphate fixation that normally occurs in O.5N Ac/ A. Except with A1₂0₃, Se/ A gave better results than 8(OH)Q. with A1₂0₃, 8(OH)Q gave slightly better results. The difference in the effectiveness of the two reagents towards Fe₂₀₃ and AI₂0₃ is not however very great. With Fe₂0₃ Se/A reduced fixation by 86 per cent and 8(OH)Q by 82 per cent. With A1₂0₃, Se/A reduced fixation by 42 per cent and 8(OH)Q by 47 per cent. These result 0 not agree with Cooke's finding that Se/A is 4 to 5 times as effective as 8(OH)Q. With Ti0₂, Se/ A reduced fixation by 15 per cent and 8(OH)Q by 3 per cent. With Mn0₂, Se/A reduced fixation by 21 per cent and 8(OH)Q by 7 per cent. It is, however, clear that Se/A on the whole is a little more effective than 8(OH)Q. with the two high- fixing oxides Fe₂0₃ and A1₂0₃, the combination reduced percentage fixation to practically nil, and with the other two oxides some reduction was affected. It is clear, therefore, that fixation of phosphorus during acid extraction can best be completely prevented by use of a combination of the two reagents.

Source of Information: Soil Sci. 84: 445-451, 1957

Article Link (Online Journal):

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The available phosphorus determined by Se/A and S/A+8(OH)Q methods in different soils show the same relative trend. Use of 8(OH)Q+ Se/A in Ac/A is suggested as the method that will yield the most satisfactory results for chemically available phosphorus.

Knowledge Management: Journal