Saturday, 15 July 2006
148-8

Extractable Phosphorus Following Fertilizer Application from Rice Soils.

Md. Rafiqul Islam and Md. Abu Saleque. Bangladesh Rice Research Institute, Gazipur-1701, Bangladesh, Gazipur, Bangladesh

Phosphorus applied to soils is specifically or non-specifically adsorbed or precipitated on the soil particles and the consequences of sorbed phosphorus are not well understood. We conducted a laboratory experiment to evaluate the efficacy of some acidic and alkaline reagents to trace the fate of sorbed phosphorus in rice soils. Soil samples were collected to use as phosphorus control (P0) and from 45 kg P ha-1 treated plots (P45) at a depth of 0 – 100 cm at 5 to 10 cm intervals. A portion of the soil sample was amended with 50 ppm phosphorus and allowed to adsorb or precipitate phosphorus for 45 days with alternate wetting and drying cycles. An untreated control was subject to the same conditions. Both the phosphorus amended and control samples were analyzed for phosphorus separately with 0.5 M NaHCO3, Bray I (0.03 N NH4F in 0.025 N HCl), Mehlich I (0.05 N HCl in 0.025 N H2SO4), Mehlich II (0.2 N HOAc in 0.015 N NH4F in 0.012 N HCl in 0.2 N NH4Cl), HCl (0.5 M HCl) and NaOH (0.1 M NaOH). Among the available indices, the mean extractable phosphorus was highest in samples treated with NaHCO3, 23% from P0 and 26% from P45 soil followed by Bray I and Mehlich I and II. On average, in samples from 0-100 cm depth about 60% of the applied phosphorus was extracted by 0.5M HCl and 50% by 0.1 M NaOH. In samples from the surface (0 –20 cm depth), recovery of phosphorus by 0.5 M HCl was 79% from P0 and 89% from P45 soil; while 0.1 M NaOH extracted 40 and 43% phosphorus from 0-20 cm depth of P0 and P45 soil, respectively. The study indicates about one-fourth of the applied phosphorus in neutral rice soils is readily available to plants and the rest is retained in the soil. However, if rice plant roots can acidify the rhizosphere, phosphorus availability may be increased to 79-89%.

Back to 3.0W Sustainable Soils and Life on Land - Poster
Back to WCSS

Back to The 18th World Congress of Soil Science (July 9-15, 2006)