Estimation of the phosphorus sorption capacity of acidic soils in Ireland

Abstract

Summary The test for the degree of phosphorus (P) saturation (DPS) of soils is used in northwest Europe to estimate the potential of P loss from soil to water. It expresses the historic sorption of P by soil as a percentage of the soil's P sorption capacity (PSC), which is taken to be α (Alox + Feox), where Alox and Feox are the amounts of aluminium and iron extracted by a single extraction of oxalate. All quantities are measured as mmol kg soil−1, and a value of 0.5 is commonly used for the scaling factor α in this equation. Historic or previously sorbed P is taken to be the quantity of P extracted by oxalate (Pox) so that DPS = Pox/PSC. The relation between PSC and Alox, Feox and Pox was determined for 37 soil samples from Northern Ireland with relatively large clay and organic matter contents. Sorption of P, measured over 252 days, was strongly correlated with the amounts of Alox and Feox extracted, but there was also a negative correlation with Pox. When PSC was calculated as the sum of the measured sorption after 252 days and Pox, the multiple regression of PSC on Alox and Feox gave the equation PSC = 36.6 + 0.61 Alox+ 0.31 Feox with a coefficient of determination (R2) of 0.92. The regression intercept of 36.6 was significantly greater than zero. The 95% confidence limits for the regression coefficients of Alox and Feox did not overlap, indicating a significantly larger regression coefficient of P sorption on Alox than on Feox. When loss on ignition was employed as an additional variable in the multiple regression of PSC on Alox and Feox, it was positively correlated with PSC. Although the regression coefficient for loss on ignition was statistically significant (P < 0.001), the impact of this variable was small as its inclusion in the multiple regression increased R2 by only 0.028. Values of P sorption measured over 252 days were on average 2.75 (range 2.0–3.8) times greater than an overnight index of P sorption. Measures of DPS were less well correlated with water‐soluble P than either the Olsen or Morgan tests for P in soil.

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].…”

“…where the saturation factor has been estimated in various studies with the value of 0.5 [33,34,40,54,55]. Van der Zee [56] reported values in the range of 0.4 to 0.6 (average of 0.5).…”

“…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.…”

Evidence for a delayed response of riverine phosphorus exports from increasing agricultural catchment pressures in the Lough Neagh catchment

“…At a laboratory scale, increasing soil P in noncalcareous soils increases water soluble P but only markedly when the degree of P saturation of soils exceeds 25% (Maguire et al 2001). This nonlinear response therefore can explain why catchment P exports did not increase until after 1960, whereas soil P had been increasing since at least 1925 and probably since 1870 (Foy et al 2002).…”

Phosphorus concentrations in subsurface water as influenced by cropping systems and fertilizer sources

“…Leinweber et al (1999) found that total P concentrations in lysimeters under 20 field sites in Germany were correlated with the DSPS, measured as the ratio of acid ammonium oxalate-extractable P to oxalate-extractable Al and Fe. Other researchers have shown that the potential for P leaching increases greatly when the DSPS, based on oxalate-extractable P, Al and Fe, exceeds 25% (Maguire et al 2001;McDowell and Sharpley 2001b). In Quebec, the DSPS method based on the ratio of Mehlich-3 extractable P to Mehlich-3 extractable Al has been adopted for acid soils with less than 6 g kg -1 of oxalate-extractable Al (Beauchemin and Simard 1999;Khiari et al 2000).…”