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

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 (X-m and a(F), respectively) and P buffering capacity (PBC). X-m, 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 X-m (r greater than or equal to0.98***), with PSI1 giving the highest correlation. As isotherms for determining P sorption capacities involve laborious analytical operations, PSI1 would be preferable for routine analyses. X-m 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. X-m was also significantly correlated with the sum of Fe and Al extracted by ammonium oxalate. The best prediction of X-m 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.