Effect of pH on the release of soil colloidal phosphorus

Abstract

Purpose Colloid-facilitated phosphorus (P) has been proved as a significant contributor to eutrophication. Release of colloidal phosphorus (P coll ) depends on the released soil colloids and their P adsorption abilities, both of which are greatly affected by pH. The aim of the study was to assess the effect of pH in a wide range on P coll loss of the top silt loamy soil rich in organic matter and P for the successful description and prediction of P transport. Materials and methods In batch experiment, soil samples were shaken with deionized water in a wide range of pH from 1.4 to 9.9 for 24 h. Then water-dispersible colloids (WDCs) were extracted by pre-centrifugation, microfiltration, and ultracentrifugation processes orderly and determined gravimetrically. The P coll values at each pH were calculated as the difference between the concentration of total P in nonultracentrifuged and ultracentrifuged samples. The same method was applied for the released colloidal mineral elements (Al, Fe, Ca, Si, Mg, Mn). Colloid morphology and P distribution on colloid surface were directly illustrated by transmission electron microscope (TEM) and scanning electron microscope-energy-dispersive X-ray spectroscopy (SEM-EDS) mapping scanning analyses. Results and discussion Over pH 4.6-6.0, the released P coll was below 5.5 mgkg -1 soil, while up to 66.8 mgkg -1 soil and 28.5 mgkg -1 soil at pH 1.4 and 9.9, respectively, indicating that both high and low pH values enhanced the mobilization of P coll . At the low pH, the potential loss of P coll mainly resulted from the dissolution of inorganic encasing cement such as Al oxides and clay mineral. However, besides electrostatic repulsion, dissolution of organic coating at high pH enhanced the P coll release as revealed by the SEM-EDS results. The P was heterogeneously distributed on the WDCs and might be associated with soil organic matter, Al oxides, Fe oxides (oxyhydroxide), and clay mineral at the low pH, while mainly with Fe oxides and less clay mineral at the high pH. Conclusions Both high and low pH enhanced colloid and P coll releases. This study first visually revealed that the dissolution of organic cement at high pH enhanced the release of WDCs and their facilitated P coll release. The exceptional loss risk of P coll may be caused by soil acidification due to the dissolution of inorganic cements, especially in Al-rich soils, and by the enhanced high soil pH due to the dissolution of organic coating in the organic matter-rich soils.

Release and migration of colloidal phosphorus from a typical agricultural field under long-term phosphorus fertilization in southeastern China

“…An aliquot of the filtrate was ultracentrifuged at 41,000 rpm for 2 h to remove colloids (Optima TL, Beckman, USA). Amount of extracted colloidal particles was determined gravimetrically (Liang et al 2010). Total P in solution was determined after digestion with acidic potassium persulfate.…”

Changes in the Activity of Phosphatase and the Content of Phosphorus in Salt-Affected Soils Grassland Habitat Natura 2000

“…Available phosphorus is only a very small fraction of total P in the terrestrial ecosystems (less than 6%). Many researchers have reported that the fractions and dynamics of P in soil also depend upon various soil characteristics such as pH (Liang et al 2010;Lemanowicz 2013), organic matter concentrations (Xiao et al 2012;Lemanowicz and Bartkowiak 2013).…”

Changes in phosphorus content, phosphatase activity and some physicochemical and microbiological parameters of soil within the range of impact of illegal dumping sites in Bydgoszcz (Poland)

“…According to Cross and Schlesinger (1995), available P is only a very small fraction of total P in the terrestrial ecosystems (less than 6 %). Many researchers have reported that the fractions and dynamics of P in soil also depend upon various soil characteristics such as pH (Liang et al 2010;Menezes-Blackburn et al 2014), heavy metals content (Amirbahman et al 2010), organic matter concentrations (Ohel et al 2004;Xiao et al 2012;Lemanowicz and Bartkowiak 2013). While according to Cao et al (2013), the P amendment may immobilize some metals (Pb, Cu, and Zn) while promoting the mobility of others.…”