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Phosphorus Fractionations in Ganges Tidal Floodplain Soil of Bangladesh

M F Hoque
Department of Soil Science, Patuakhali Science and Technology University, Dumki, Patuakhali.

M S Islam
Department of Soil Science, Patuakhali Science and Technology University, Dumki, Patuakhali.

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

M H Rashid
Department of Agronomy, Patuakhali Science and Technology University, Dumki, Patuakhali.

M A Saleque
Coordinator for Advanced Studies and Research, Bangladesh Rice Research Institute, Gazipur 1701.

Abstract/ Executive Summary:

The present investigation aimed to evaluate different fractions of P of Ganges tidal floodplain soils of Bangladesh in terms of plant availability in the selected soil. The samples were analyzed for solution P, labile pool, alkali-extracted inorganic pool, organic pool, acidic pool and residual P. The soil solution P in the tested soils ranged from 0.03 to 0.11 mg L^–1. The concentration of 0.5M NaHCO₃ extracted P had a range of 8-34 mg kg^–1. Dilute NaOH extracted inorganic P had a range of 25-59 mg kg^–1. NaOH extracted organic P ranged from 334 to 542 mg kg^–1 and acid extracted P represented from 140 to 443 mg kg^–1, respectively. Residual P of the tested soils showed a concentration of 104-262 mg kg^–1. On average of the 12 soils, the relative concentration of solution P was 0.01%, NaHCO₃ P was 3.2%, NaOH-Pi was 6.8%, NaOH-Po was 44.6%, acid pool was 27.3% and residual fraction was 18.1%. Different P pools showed strong correlation either with sand, silt, clay, electrical conductivity, pH(H₂O), pH (KCl), pH, organic carbon or extractable Fe content. The tested Ganges tidal floodplain soils demonstrated wide variation in the relative proportion of different P pools.

Keywords: Tidal floodplain, Solution P, Inorganic P, Organic P, Acid P, Labile P, Stable P, Residual P

Location: Patuakhali, Borguna, Barisal and Bhola districts

Start Date: 00-01-2008

End Date: 00-03-2008

Program Area: Crop-Soil-Water Management

Commodity: Soil fertility

Objectives:

To determine the distribution of soil P fractions in selected rice growing Ganges tidal floodplain soils.

Methodology:

Twelve surface (0 - 15 cm) soil samples used for the fractionation study were collected from cultivated rice fields in January to March 2008 after T. Aman harvest. The selected soil sampling sites were of different upazilas (Dumki, Kalapara, Amtali, Wuzirpur, Gouranadi, Borhanuddin, Lalmohan) of Patuakhali, Borguna, Barisal and Bhola districts. According to USDA soil taxonomy, these have been classified as TypicEdoaquept, TypicHaplaquept, AericHaplaquept, Thapto - Histic Haplaquept, AquicEutrochrept and Histosols. For the convenience of discussion, the 12 soils are referred to as soil 1 through soil 12. The collected soil samples were air - dried and ground to pass a 2 - mm sieve and then mixed to form a composite sample. Soils were analyzed in Soil Science laboratory and Central laboratory of Patuakhali Science and Technology University during January 2008 to April 2008. The sand, silt and clay content of soils were determined using the hydrometer method. Soil pH_H2O was measured in a 1:2.5 soil water ratio, using glass electrode pH meter method, and the pH KCl was also measured by using a 1.0 M KCl in a similar manner as in pH_H2O determination. Organic carbon of soil was determined. Mehlich-3 (M3) extractable P was determined by using the Mehlich-3 extraction method. Available Fe was determined by sodium dithionate - citrate system buffered with sodium bicarbonate.The experiment was conducted in a complete randomized block design with three replications. One g air - dried soil was taken in 50 ml centrifuge tube for P fractionation study. One run of the analysis was considered as one replication. Fractionation of inorganic P was performed on each soil following Saleque et al. method modified from P fractionation scheme of Sui et al .. The following soil P fractions were measured in sequence: i) Solution P, by shaking 1 g soil in 30 ml of 0.05M CaCl₂ for 16 hours, centrifuging, filtering and measuring P in the filtrate. ii) NaHCO₃ - P, by shaking the residue from (i) in 30 ml 0.5M NaHCO₃ for 16 hours, centrifuging, filtering and measuring P in the filtrate. iii) NaOH - Pi, by shaking the residue from (ii) in 30 ml 0.1M NaOH for 16 hours, centrifuging, filtering and measuring P in the filtrate after acidifying with 5 ml concentrate HCl. iv) NaOH - Po, by digesting 5 ml of the filtrate from (iii) in 6 ml of concentrate H₂SO₄ for 1 hour, cooling, adding 5 ml of H₂O₂ and reheating until the residue becomes white, determining P in the digest and subtracting the NaOH - Pi from it. v) Acid - P, by shaking the residue from (iii) in 30 ml 1:1 mixture of 1M HCl/1M H₂SO₄ , centrifuging, filtering and measuring P in the filtrate. vi) Residual - P, by fluxing the soil residue from (v) in 6 ml of a 5:2 mixture of concentrated HNO₃ and HClO₄ and determining P from the digest. All P was determined colorimetrically after neutralization when necessary with dilute HCl and NaOH and the neutral pH indicated by the slight yellowish colour of the solution in the presence of p - nitrophenol indicator. Absorbance of P was determined at a wavelength 712 nm by spectrophotometer. All measurements of P were done in duplicate and the data were analyzed by Excel software.

Source of Information: Bangladesh Rice j. 19(2): 55-61, 2015, ISSN: 1025-7330

Article Link (Online Journal): DOI: http://dx.doi.org/10.3329/brj.v19i2.28165

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Soil P is distributed in solution, NaHCO₃ - P, NaOH - Pi, NaOH - Po, acid and residual P fractions. On an average of the 12 soils, the relative concentration of native soil P was 0.01% in solution P, 3.2% in NaHCO₃ P, 6.8% in NaOH - Pi, 44.6% in NaOH - Po, 27.3% in acid pool and 18.2% in residual fraction. However, there was large variation in the distribution of different P fractions of tidal floodplain soils of Bangladesh. This information would be helpful for recommendation of phosphorus in the respective areas.

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