Colloidal and Dissolved Phosphorus in Sandy Soils as Affected by Phosphorus Saturation

Abstract

Fertilization exceeding crop requirements causes an accumulation of phosphorus (P) in soils, which might increase concentrations of dissolved and colloidal P in drainage. We sampled soils classified as Typic Haplorthods from four fertilization experiments to test (i) whether increasing degrees of phosphorus saturation (DPS) increase concentrations of dissolved and colloidal P, and (ii) if critical DPS levels can be defined for P release from these soils. Oxalate-extractable concentrations of P, iron (Fe), and aluminum (Al) were quantified to characterize DPS. Turbidity, zeta potential, dissolved P, and colloidal P, Fe, Al, and carbon (C) concentrations were determined in water and KCl extracts. While concentrations of dissolved P decreased with increasing depth, concentrations of water-extractable colloidal P remained constant. In topsoils 28 +/- 17% and in subsoils 94 +/- 8% of water-extractable P was bound to colloids. Concentrations of dissolved P increased sharply for DPS > 0.1. Colloidal P concentrations increased with increasing DPS because of an additional mobilization of colloids and due to an increase of the colloids P contents. In addition to DPS, ionic strength and Ca(2+) affected the release of colloidal P. Hence, using KCl for extraction improved the relationship between DPS and colloidal P compared with water extraction. Accumulation of P in soils increases not only concentrations of dissolved P but also the risk of colloidal P mobilization. Leaching of colloidal P is potentially important for inputs of P into water bodies because colloidal P as the dominant water-extractable P fraction in subsoils was released from soils with relatively low DPS.

Molecular Speciation of Phosphorus Present in Readily Dispersible Colloids from Agricultural Soils

“…This confirmed previous studies showing the dominance of P coll in water-extracted P in different agricultural lands (Ilg et al, 2005;Zang et al, 2013). For both studied soils, MRP coll comprised a substantial component of TP coll (RS, 59.7%; VS, 72.9%).…”

“…This fractionation neglects mobile colloids, particles ranging from 1 nm to 1 mm (Baalousha et al, 2005), by which P could be transported across long distances. Accumulated evidence indicates that colloid-facilitated P transport is an important mechanism for P transfer from agricultural land to aquatic ecosystems (Heathwaite et al, 2005;Ilg et al, 2005;Siemens et al, 2008;Regelink et al, 2013). Colloidal P (P coll ) has been reported to contribute >50% of total P (TP) in soil water samples (Hens and Merckx, 2001).…”

“…Detailed information on these soil samples can be found in our previous study (Liu et al, 2013). Water-dispersible colloids (WDCs), generally an indicator of readily mobile colloids (de Jonge et al, 2004), were isolated and measured following a modified procedure of Ilg et al (2005). For the modification, a 1-mm microporous membrane instead of a 1.2-mm filter was used to isolate WDCs according to the definition of colloids with at least one-dimension size ranging from 1 nm to 1 mm by IUPAC (Baalousha et al, 2005).…”

Numerical Application to Monitor Diffusion Pressure on the Deposition of Fungi in Slight Heterogeneous Phreatic Deposition

“…This can have serious negative implications. Daniel et al (1998) found that concentrations of P critical for terrestrial plant growth were an order of magnitude larger than concentrations at which lake eutrophication may occur Subsurface P transport is a less studied and understood transport mechanism compared to transport by overland flow, although abundant studies have reported its occurrence [1][2][3][4][5]. For example, Andersen and Krovang (2006) modified a P Index to integrate potential P transport pathways of tile drains and leaching in Denmark.…”

Assessment of a Large Subsurface Controlled Drainage and Irrigation System: III. Water chemistry of the tile effluent and its potential impact on surface water resources

“…Surface water runoff of N and P are particularly associated with watersheds having an intense livestock or poultry presence (Akhtar et al, 2005), where the soils have been heavily fertilized (Moore and Edwards, 2005;Davis et al, 2000) or are in proximity to surface waters (Elliott et al, 2006;Gburek et al, 2000;Langlois and Mehuys, 2003;Page et al, 2005). Nitrate concentrations from subsurface drainages frequently exceed the USEPA maximum contamination levels (Abrahamson et al, 2006;Davis et al, 2000;Randall et al, 2003; and P concentrations may also be a concern, especially where the soils have a low P sorption capacity and elevated P concentrations (Djodjic et al, 2004;Ilg et al, 2005;Page et al, 2005;Anderson and Magdoff, 2005;Langlois and Mehuys, 2003;Stampfli and Madramootoo, 2006). Thus, soil classification and characterization, cropping systems and irrigation/drainage systems interact to produce various pathways for N and P to impact surface water.…”