Phosphorus (P) sorption properties are poorly documented for Swedish soils. In this study, P sorption capacity and its relation to soil properties were determined and evaluated in 10 representative Swedish topsoils depleted in available P. P sorption indices were estimated from sorption isotherms using Langmuir and Freundlich equations (Xm and aF, respectively) and P buffering capacity (PBC). Xm ranged from 6.0 to 12.2 mmol kg−1. All indices obtained from sorption isotherms were significantly correlated with each other (r=0.96*** to r=0.99***). Two single-point sorption indices (PSI1 and PSI2) were also determined, with additions of 19.4 and 50 mmol P kg−1 soil, respectively. Both PSI indices were well correlated with Xm (r≥0.98***), with PSI1 giving the highest correlation. As isotherms for determining P sorption capacities involve laborious analytical operations, PSI1 would be preferable for routine analyses. Xm was significantly correlated with Fe extracted by sodium pyrophosphate and ammonium oxalate, to Al extracted by ammonium oxalate and dithionite-citrate-bicarbonate and to organic c. Xm was also significantly correlated with the sum of Fe and Al extracted by ammonium oxalate. The best prediction of Xm through multiple regression was obtained when Fe extracted in ammonium oxalate and Al extracted in dithionite-citrate-bicarbonate were used. Based on the results obtained, both PSI1 and oxalate-extractable Fe plus Al can be used for predicting P sorption capacity in Swedish soils.

Phosphorus sorption in relation to soil properties in some cultivated Swedish soils.

Runoff P associated with eroded soil is partly solubilized in receiving waters and contributes to eutrophication, but the significance of particulate phosphorus (PP) in the eutrophying P load is debatable. We assessed losses of bioavailable P fractions in field runoff from fine-textured soils (Cryaquepts). Surface runoff at four sites and drainflow at two of them was sampled. In addition to dissolved molybdate-reactive phosphorus (DRP) losses, two estimates of bioavailable PP losses were made: (i) desorbable PP, assessed by anion exchange resin-extraction (AER-PP) and (ii) redox-sensitive PP, assessed by extraction with bicarbonate and dithionite (BD-PP). Annual losses of BD-PP and AER-PP were derived from the relationships (R 2 = 0.77-0.96) between PP and these P forms. Losses of BD-PP in surface runoff (94-1340 g ha -1 ) were typically threefold to fivefold those of DRP (29-510 kg ha -1 ) or AER-PP (13-270 g ha -1 ). Where monitored, drainflow P losses were substantial, at one of the sites even far greater than those via the surface pathway. Typical runoff DRP concentration at the site with the highest Olsen-P status (69-82 mg kg -1 ) was about 10-fold that at the site with the lowest Olsen P (31-45 mg kg -1 ), whereas the difference in AER-PP per mass unit of sediment was only threefold, and that of BD-PP 2.5-fold. Bioavailable P losses were greatly influenced by PP runoff, especially so on soils with a moderate P status that produced runoff with a relatively low DRP concentration.

Contribution of particulate phosphorus to runoff phosphorus bioavailability.

Use of blast furnace granulated slag as a substrate in vertical flow reed beds: Field application

http://pure.au.dk/portal/files/40578275/Jenssen_P.D._2010_Ecol._Eng._36_Filter_bed_systems_treating_domestic_wastewater_in_the_Nordic_countries_Performance_and_reuse_of_filter_media.pdf

Filter bed systems treating domestic wastewater in the Nordic countries - Performance and reuse of filter media

The potential bioavailability of phosphorus in agriculturally loaded rivers of southern Finland was determined by an algal bioassay and the release of the potentially bioavailable particulate P was estimated by sorption studies. According to the bioassay 0 to 13.2 per cent (mean 5.1%) of the particulate P in river water samples was potentially bioavailable. Dissolved reactive P (DRP) in river waters appeared to be totally bioavailable whereas the dissolved unreactive P appeared not to be utilized by algae. In addition to river waters two lake sediment samples were also assayed. In these samples 0 and 2.6% of the P was bioavailable. The potential bioavailability of particulate P in agriculturally loaded rivers obtained in this study was lower than that reported in studies from other countries. The difference was assumed to arise partly from methodological factors and partly from the nature of the Finnish soils. The EPC (equilibrium phosphate concentration) values indicated that during the period when most of the agricultural loading enters the lakes in Finland, potentially bioavailable P is not released from the particles because of the relatively high DRP concentration in the receiving waters. However, during the algal production period the DRP concentration in lakes decreases below the EPC and potentially bioavailable particulate P is desorbed. The increase in pH during this period may further enhance the desorption of P.

H. Hartikainen

Papers

Phosphorus and its reactions in terrestrial soils and lake sediments [P]