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Evaluation of Soil Test Methods for Phosphorus and Its Critical Limit for Wheat in Some Soils of Bangladesh

M.Q. Haque
Soil Science Division, BINA, Mymensingh

G.K.M.M. Rahman
Soil Science Division, BINA, Mymensingh

M.I. Ali
Soil Science Division, BINA, Mymensingh

M.H. Rahman
Soil Science Division, BINA, Mymensingh

Abstract/ Executive Summary:

An investigation was undertaken with an objective to find out P extractability of various extractants and determining its critical limit for wheat. The amount of extractable P varied markedly depending on the soils and extractants used. Considering the average of 16 soils, the maximum amount of P (32.4 ppm) was extracted by Nelson (0.5N HCI + 0.02 N H₂S0₄) method and the minimum (15.3 ppm) by Olsen 0.5 N NaHC0₃ pH 8.5) method. For all soil series P extracting power of the extractants were in the descending order of Nelson> Truog> Bray> Hunterc>Olsen. The amount of P solubilized by every pair of extractants were significantly and positively correlated with each other. The results showed significant and positive correlation of extractable P with dry matter yield and also with relative yield. None of the extractants showed significant correlation with plant P content. Hunter's method (0.25N NaHC0₃ +0.01N EDTA 1 : 10+ O.01N NH₄F) of pextraction was found to be the best for predicting P response for wheat and demonstrated 12.5 ppm as its critical limit.

Keywords: Evaluation, Soil, Phosphorus, Wheat

Location: Soil Science Division, BINA, Mymensingh

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Wheat, Soil fertility

Objectives:

To identify the soil P extracting ability of different extractants and for determining its critical limit for wheat in 16 Bangladesh soils.

Methodology:

Sixteen soil samples each representing a soil series, (0-15 cm) were collected from different locations of Bangladesh. Each soil sample was analyzed for extractable P by five extraction methods. A pot culture experiment was conducted using wheat as the test crop. There were three P treatments viz., 0, 100 and 200 ppm P(soil basis). A basal application of 100, 100,40 and 10 ppm solution of N, K, S, and Zn were added at the rate of 20 ml/pot in the form of NH₄NO₃, KCI, CaSO_4, 2H₂O and ZnCl₂ respectively. P was also added in the form of solution from KH₂P0₄. All the nutrient solutions were mixed thoroughly with the soil. Treatments were replicated thrice in a completely randomized design. Fifteen wheat seeds (Var. Balaka) were sown in each pot and after emergence, seedlings were thinned to 12 per pot. Plants were cut at ground level after 42 days of sowing followed by washing with distilled water and drying in an oven at 65⁰C for 24 hours. Dry matter yield (oven dry basis) was recorded. The dried plant samples were grounded, digested with H₂S0₄ +HCI0₄ mixture and phosphorous was determined by developing vanadomolybdophosphate yellow colour as described. The critical levels of extractable P for wheat was determined by two different approaches, the one is graphical and the other statistical.

Source of Information: Bangladesh Journal of Nuclear Agriculture. Vol: 12, pp: 31-37, 1996

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The amount of P solubilized by every pair of extractants were significantly and positively correlated with each other. The results showed significant and positive correlation of extractable P with dry matter yield and also with relative yield. None of the extractants showed significant correlation with plant P content. Hunter's method (0.25N NaHC0₃ +0.01N EDTA 1 : 10+ 0.01N NH₄F) of Pextraction was found to be the best for predicting P response for wheat and demonstrated 12.5 ppm as its critical limit.

Knowledge Management: Journal