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Phosphorus Fractionation in Acid Soil of Lakkatura Tea Garden, Sylhet, Bangladesh

M.R. Islam
Department of Soil Science, Bangladesh Agricultural University, Mymensingh, Bangladesh

M Rony
Department of Soil Science, Bangladesh Agricultural University, Mymensingh, Bangladesh

H. Afroz
Department of Soil Science, Bangladesh Agricultural University, Mymensingh, Bangladesh

M.S. Islam
Department of Agronomy, Bangladesh Agricultural University, Mymensingh, Bangladesh

M.M. Hoque
Department of Food Engineering and Tea Technology, Shahjalal University of Science and Technology, Sylhet.

Abstract/ Executive Summary:

Phosphorus (P) availability is affected in acid soils and hence it is important to monitor the distribution of P in acid soils. A study was undertaken to evaluate the distribution of P and its relationship with other nutrients. The soil samples were collected at 0-15 cm and 15-30 cm depths from 0 year, 20 year, 40 year and 60 year tea cultivated soils. The P fractions determined were total P, total organic P, total inorganic P and available P. The available P in soils was extracted with four different extractants viz. Olsen, Bray, Nelson and Morgan extractants. The different P fractions varied in their levels and also decreased in subsurface soils. In general, the P fractions were significantly and positively correlated with organic matter, total N and available S contents of soils and negatively correlated with soil pH. The total P content varied from 80.08 to 96.81 ppm at 0-15 cm depth and from 67.73 to 81.95 ppm at 15-30 cm depth in different soils. Among the soils the highest organic P (59.20 ppm) was found in soils of 40 years of tea cultivation. The inorganic P content of soils varied from 29.62 to 37.61 ppm at 0-15 cm depth and from 28.29 to 34.66 ppm at 15-30 cm depth. The organic and inorganic P constituted on an average 59.90% and 40.10% of total P, respectively. The available P content varied considerably with the variation of soils and extractants used. The highest available P content was observed in 40 year aged tea soil with all the extractants while 0 year round cultivated tea soil showed the lowest value. The P values extracted by different extractants followed the order of Bray-P>Nelson-P>Olsen-P>Morgan-P.

Keywords: Phosphorus fractions, Acid soils, P extractants

Location: Lakkatura Tea Garden, Sylhet

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Soil Health

Objectives:

To evaluating the P fractions in soils and their distribution for proper management of P in soils.

Methodology:

The representative soil samples were collected from four different age group of tea crop grown for 0 year, 20 year, 40 year and 60 year in Lakkatura Tea Garden, Sylhet. The soils belong to the Agro-ecological Zone 20 designating Eastern Surma-Kushyara Floodplain. Twenty four composite soil samples were collected from the sampling sites at two different depths of 0-15 cm and 15-30 cm. Soil samples were carried to the laboratory, dried at room temperature, mixed thoroughly, crushed, sieved with a 10-mesh sieve and preserved in plastic bags for subsequent laboratory analyses. Total P in the soil was extracted by digestion with HClO₄ and HNO₃ mixture (HClO₄ : HNO₃ = 1 : 2) as outlined by Jackson (1958). For determining organic P, the soil sample was ignited with HCl at 240^oC for 1 hour in a Pyrex beaker and then P was extracted from the soil with NH₄Mo-HCl solution (Olsen et al. 1954). Inorganic phosphorus was determined by subtracting organic phosphorus from the total phosphorus. Available P was extracted from the soil by four different extractants. The phosphorus in the extract was determined turbidimetrically. Particle size analysis of soil was done by hydrometer method (Bouyoucos 1927) and the textural class was determined by plotting of the values for %sand, %silt and %clay on the Marshall’s Triangular Coordinate (Marshall 1947) following the USDA system. Organic matter was determined by Walkley and Black method (Walkley and Black, 1934). The soils were also analyzed for pH (1:2.5 soil-water) by glass electrode pH meter method(Michael 1965), total N by Semi-micro Kjeldahl method (Bremner and Mulvaney, 1982), available P by Olsen method (Olsen et al. 1954), exchangeable K by Flame Photometer after extraction with 1N NH₄OAc at pH 7.0 (Knudsen et al. 1982) and CEC (Chapman 1965). Mean, standard deviation and simple correlation were carried out to validate the results.

Source of Information: J. Soil Nature 7(1):1-6 (March 2014)

Article Link (Online Journal): http://ggfjournals.com/e-journals archive

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The overall results indicate that the status of various P fractions varied from soil to soil and in some soils the level of available P recorded only a small portion of the total P (0.01%) indicating the existence of P deficiency. The inorganic P content of soils was low in comparison with organic P in different soils. Bray extractant produced the highest available P compared to that extracted with other extractants. Among these four age groups of tea soils, 40 year tea cultivated soil was found to be rich in different P fractions due to management practices over the years.

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