Changes in water-extractability of soil inorganic phosphate induced by chloride and sulfate salts

• Published in: Environmental science and pollution research international 2008, Vol.15 (1), p.23-26
• Main Authors: Ahmad, Zahoor, Faridullah, El-Sharkawi, Haytham, Irshad, Muhammad, Honna, Toshimasa, Yamamoto, Sadahiro, Al-Busaidi, Ahmed Salim
• Format: Article
• Language: English
• Subjects: Adsorption; Anions; Aquatic Pollution; Atmospheric Protection/Air Quality Control/Air Pollution; Cations; Chemistry Techniques, Analytical; Chloride; Chlorides - chemistry; Desorption; Earth and Environmental Science; Ecotoxicology; Environment; Environmental Chemistry; Environmental Health; Ions; Livestock; Manures; Phosphates - chemistry; Phosphates - isolation & purification; Phosphorus; Phosphorus removal; Pollution; Research Article; Saline soils; Salt; Salts; Sodium chloride; Sodium sulfate; Soil - analysis; Soil contaminants; Soil testing; Solubility; Sorption; Studies; Sulfates; Sulfates - chemistry; Waste Water Technology; Water - chemistry; Water Management; Water Pollution Control
• ISSN: 0944-1344; 1614-7499
• DOI: 10.1065/espr2006.06.309

Goal, Scope and Background One of the principal experimental variables which effect the results of phosphorus (P) sorption studies is the ionic composition, in addition to both species and concentrations of the contacting solution. In spite of the realization that ionic species, concentrations and their compositions effect P sorption and/or desorption, most of the salt-related studies are confined to Cl − (anion) in association with different cations. While the knowledge about the comparative response of P to Cl − and SO 4 2− ions was lacking, the current study was conducted to evaluate the comparative effects of anions (in association with cations) on inorganic P release and P fractions in the soil. Methods The test soil was amended with livestock compost manure (OP); KH 2 PO 4 (IPk) or Ca(H 2 PO 4 ) 2 (IPc) at a rate of 1ppm. Soil was subjected to one salt and nine subsequent water extractions and different P fractions were measured. Four salt types, NaCl, Na 2 SO 4 , KCl and K 2 SO 4 , were used at levels of 0.5 M. Results Irrespective of P sources, P release was substantially increased in the salt-pretreated soil as compared to the non-saline soil. Sulfate salts released more P in subsequent water extractions than Cl − . Phosphorus release decreased for salt types with Na 2 SO 4 > NaCl> K 2 SO 4 > KCl and for P sources with OP ∼IPk > Control (without P application) > IPc, respectively. Discussion No previous study was found to compare the results of more P release by SO 4 2− than Cl − salt. Most of the previous studies focused on anion sorption capacities, but the mechanism for their adsorption is not fully known. Most of the authors suggested that the mechanisms of SO 4 2− and PO 4 3− adsorption are similar, and that both ions compete for the same sorption sites (Kamprath et al. 1956, Couto et al. 1979, Pasricha and Fox 1993). Although adsorbed SO 4 2− does not compete strongly with PO 4 3− , there is likely to be some competition for sorption between these anions which may cause comparatively more P release by SO 4 2− than Cl-salts. Higher P release by Nasaturation could be due to the release of P associated with oxide surfaces or due to dissolution of Ca-P phases (Curtin et al. 1987). Conclusions Study clearly showed that not only cations species differ for P desorption capacity, but associated anions also play a vital role in the fate of P under saline environments. Synergetic effects exist between Na and SO 4 2− ions which enhanced the P release.