A mechanistic model for describing the sorption and desorption of phosphate by soil

Abstract

Summary A model of phosphate reaction is constructed and its output compared with observations for the sorption and desorption of phosphate by soil. The model has three components: first, the reaction between divalent phosphate ions and a variable‐charge surface; second, the assumption that there is a range of values of surface properties and that these are normally distributed; third, the assumption that the initial adsorption induces a diffusion gradient towards the interior of the particle which begins a solid‐state diffusion process. The model closely describes the effects on sorption of phosphate of: concentration of phosphate, pH, temperature, and time of contact. It also reproduces the effects on desorption of phosphate of: period of prior contact, period and temperature of desorption, and soil: solution ratio. The model is general and should apply to other specifically adsorbed anions and cations. It suggests that phosphate that has reacted with soil for a long period is not ‘fixed’ but has mostly penetrated into the soil particles. The phosphorus can be recovered slowly if a low enough surface activity is induced.

Phosphorus Sorption Kinetics in Reclaimed Lignite Mine Soils under Different Age Stands ofRobinia pseudoacaciaL. in Northeast Germany

“…The P sorption increased rapidly with time until about 48 h reaction time and continued for a longer time, even though the sorption rates became slower. This sorption behaviour is typical and is well reported in the literature [26,34,88].…”

“…Therefore, it is important to understand the kinetics of P sorption in this "initial soil" in order to describe the P bioavailability and P mobility. Several studies have been carried out on soil P sorption and desorption kinetics in agroecosystems [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43], and various techniques have been employed to investigate P (de)sorption from soils [29,30,32,44,45]. However, few studies [22,46] concentrated on P sorption in mining soils.…”

Effects of Pig Slurry Application and Crops on Phosphorus Content in Soil and the Chemical Species in Solution

“…Aside from the organic compounds, an increase in the SO 4 2-concentration in solution, especially in soil treated with PS rates of 40 and 80 m 3 ha -1 (Table 1), may have promoted competition for the functional groups of the surface of reactive particles, increasing the desorption of P retained with less energy (Meurer, 2010). Also, the increase in pH in the solution in the 2 nd sampling in all treatments probably promoted the deprotonation of surface functional groups, reducing P adsorption (Barrow, 1983). It should be stressed that at the lower K d value observed in the 0-5 cm layer in the 2 nd sampling, treated with 80 m 3 ha -1 PS, the soluble P concentration represented 0.4 % of the total content, which is higher than 0.1 %, the normal value in agricultural soils (Loehr, 1984).…”

“…In soil, P is adsorbed to the functional groups of inorganic particles, forming an inner-sphere complex (Barrow, 1983) and therefore, P mobility and concentration in the soil solution are low (Frossard et al, 2000). However, when P is added successively and at high rates to the soil, for example by PS application in crop conservation systems such as no-tillage (NT), where the soil is not tilled, the total P content may increase (Berwanger et al, 2008;Lourenzi et al, 2014), and especially the content available to plants, which can be diagnosed by the method of Mehlich-1 (Gatiboni et al, 2008;Guardini et al, 2012).…”

Understanding ecosystem retrogression

“…Therefore, in the early and intermediate stages of soil development, abiotic P supply is controlled by a combination of primary mineral dissolution and adsorption-desorption reactions associated with secondary minerals (Tiessen 2005). However, with time, the inorganic P adsorbed on oxide mineral surfaces becomes occluded and less readily desorbed due mainly to a combination of solid-state diffusion of P into the mineral structure and deposition of new minerals on oxide surfaces (Barrow 1983). The physicochemical occlusion of adsorbed P, together with formation of recalcitrant P minerals by reaction with iron, aluminum and calcium released during weathering, significantly reduces the bioavailability of inorganic P during the advanced stages of soil development (Adams and Walker, 1975, Cross and Schlesinger 1995, Tiessen 2005).…”