Mclaren, T.Simpson, R.Mclaughlin, M.Smernik, R.Mcbeath, T.Guppy, C.Richardson, A.2015-08-182015-08-182015Journal of Plant Nutrition and Soil Science, 2015; 178(4):543-5541436-87301522-2624http://hdl.handle.net/2440/93651Phosphorus fertilizer use efficiency of pastures is often low because P accumulates in soils as sparingly-available forms of inorganic and organic P. The aim of this study was to use sequential chemical fractionation to identify which forms of P have accumulated in soil under permanent pasture from a medium-term (13 y) field experiment. Treatments included an unfertilized pasture (P0), and treatments designed to maintain soil P fertility at near ‘optimum’ (P1) and ‘supra-optimum’ (P2) levels for pasture growth; all levels of soil P fertility were continuously grazed with either a moderate or high stocking rate (SR09 and SR18). Summed concentrations of extractable inorganic and organic P, and residual P (i.e., non-extractable P) accounted for 20, 31, and 49% of total soil P (as determined by laboratory X-ray fluorescence), respectively, across all surface (0–10 cm) and subsurface (10–20 cm) soil layers. A large proportion of extractable inorganic and organic P was contained in the NaHCO3 and NaOH soluble fractions across all surface soil layers, and these fractions were also the most important sinks for fertilizer P. The accumulation of organic P appeared to plateau with increasing fertilizer addition, whereas inorganic P continued to increase. The majority of the P that had been applied as fertilizer (70%) was recovered in the surface soil layer (0–10 cm). Approx. 31 and 30% of the added P was recovered in the summed concentrations of extractable inorganic and organic P, respectively, of the surface soil layer at the optimum (P1) agronomic level of soil P fertility.en© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimImproved grasslands; phosphorus dynamics; phosphorus use efficiency; sequential chemical fractionation; superphosphateJournal article003003196910.1002/jpln.2014006570003590627000012-s2.0-849384227162-s2.0-84933054660194330Mclaughlin, M. [0000-0001-6796-4144]Smernik, R. [0000-0001-6033-5855]Mcbeath, T. [0000-0001-6423-367X]