McBeath, T.McLaughlin, M.Kirby, J.Armstrong, R.2012-10-312012-10-312012Plant and Soil: international journal on plant-soil relationships, 2012; 358(1-2):337-3480032-079X1573-5036http://hdl.handle.net/2440/73841Background and aims Crop phosphorus (P) content is controlled by P uptake from both banded P fertiliser and from P throughout the soil profile. These P supply factors are in turn controlled by soil, climatic and plant factors. The aim of this experiment was to measure the contribution of fertiliser, topsoil and subsoil P to wheat plants under wet and dry growing season conditions. Methods An isotopic tracer technique was used to measure P uptake from fertiliser at seven agricultural field sites under wet and dry growing season conditions. At three of these sites a dual isotopic technique was used to distinguish between wheat uptake of P from fertiliser, topsoil (0–15 cm) and subsoil (below 15 cm). Results The amount of P fertiliser used by wheat was in the order of 3–30% of the P applied and increased with increasing rainfall. Topsoil P was the most important P source, but when sufficient P was present in the subsoil, P fertiliser addition stimulated the use of subsoil P. Conclusions Most crop P uptake was from the topsoil, however P fertiliser banded below the seed increased plant P uptake and stimulated the use of subsoil P in one soil type in a decile 7 (above average rainfall) growing season.en© Springer Science+Business Media B.V. 2012Fertiliser efficiencyIsotopic tracingIsotopic dilutionDroughtCrop nutritionJournal article002010218710.1007/s11104-012-1177-80003081904000272-s2.0-8486536613932649McBeath, T. [0000-0001-6423-367X]McLaughlin, M. [0000-0001-6796-4144]