Phosphorus fractionation and sorption in P-enriched soils of Norway B.R. Singh 1, *, T. Krogstad 1 , Y.S. Shivay 1,2 , B.G. Shivakumar 1,2 and M. Bakkegard 1 1 Department of Plant and Environmental Sciences, Norwegian University of Life Sciences Norway, P.O. Box 5003, N-1432 A ˚ s, Norway; 2 Division of Agronomy, Indian Agricultural Research Institute, 110 012, New Delhi, India; *Author for correspondence (e-mail: balram.singh@ umb.no; fax: +47-64-94-8211) Received 10 June 2004; accepted in revised form 1 September 2005 Key words: P availability, P fractions, Soil properties Abstract Phosphorus (P) enrichment can lead to imbalance in nutrient availability and pollution of terrestrial and aquatic ecosystems. Hence studies were carried out to investigate fractionation and sorption of P in eleven P-enriched soils collected from different agro-climatic sites in Norway. Different P fractions viz. total, organic, inorganic (easily soluble P, Fe-P, Al-P, Ca-P and occluded P), P w (water extractable), and NH 4 - lactate extractable P (P AL ) at the beginning and after the completion of the experiments varied widely among the soils studied, indicating a wide variability of P supplying capacity of these soils. Soluble P was positively correlated to Ca-P (r = 0.94; P < 0.001), P w (r = 0.87; P < 0.001), pH (r = 0.79; P < 0.01) and P AL (r = 0.79; P < 0.01), whereas it was negatively correlated with ammonium oxalate-extractable Al (Al ox )(r = 0.68; P < 0.05). Iron-P was only moderately related to Al ox (r = 0.64; P < 0.05) and P ox (r = 0.70; P < 0.05), whereas it was not related to any of the other parameters tested. The a [a =P ox / (Fe ox + Al ox )] was highly correlated with P AL (r = 0.93; P < 0.001), pH (r = 0.87; P < 0.001), inorganic P(r = 0.80; P < 0.01) and P w (r = 0.77; P < 0.01) but moderately to total P (r = 0.71; P < 0.05). Adsorption data fitted well to the Langmuir equation for most soils. The P affinity constant (k), adsorption maximum (b) and thus maximum buffering capacity (mbc) and adsorption isotherm of P were highest in the sandy clay soil from Øsaker, which also contained high amounts of Fe, Al and clay particles and the lowest in sandy soil from Vestra˚ len, which contained very high initial P AL and the lowest content of Fe, Al, silt and clay among all the soils studied. The P affinity constant (k) was correlated positively and significantly to clay content (r = 0.66; P < 0.05), whereas mbc was correlated positively and significantly to clay content (r = 0.63; P < 0.05) and ammonium oxalate-extractable Fe (Fe ox )(r = 0.63; P < 0.05). Phosphorus desorption of the soils varied widely depending on the initial P status and texture of the soils. Phosphorus desorbed by NH 4 -lactate was many fold higher as compared to CaCl 2 in most soils. Introduction Phosphorus is one of the key nutrients needed for successful agriculture. However, its indiscriminate use may result in its build up in the soil. This build up of residual phosphorus in soil can lead to imbalance of nutrient availability to crop plants (Ryan et al. 1995; Ashtab and Yel’nikov 1996), pollution of terrestrial and aquatic ecosystems in due course of time (Reed et al. 2000). Indiati and Rossi (1999) reported that a value of 100 mg kg 1 soil for Olsen-extractable P corresponds to a degree of phosphorus saturation value of 25%, which represents a critical level to distinguish soils Nutrient Cycling in Agroecosystems (2005) 73:245–256 Ó Springer 2005 DOI 10.1007/s10705-005-2650-z