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Phosphorus auditing cannot account for all the phosphorus applied to different pasture soils


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Burkitt, LL, Gourley, CJP and Sale, PWG 2004 , 'Phosphorus auditing cannot account for all the phosphorus applied to different pasture soils' , Australian Journal of Soil Research, vol. 42 , pp. 89-98 , doi: 10.1071/SR03025.

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Five field sites established in the high rainfall zone of southern Victoria were used to examine the downwards vertical movement of phosphorus (P) fertiliser on soils which ranged in P sorption capacity. Fertiliser was applied either as a single application of 280 kg P/ha at the beginning of the experiment (April 1998), or as 35 kg P/ha reapplied every 6 months (totalling 210 kg P/ha by the end of the third year). Soil cores were sampled in June 2001 to a depth of 40 cm, and soil at depths of 0-5, 5-10, 10-20, 20-30, and 30-40 cm was analysed for a range of soil properties and total P concentration. Total P concentration changed very little down the profile, indicating that there was minimal vertical movement of P fertiliser below the 10 cm layer of 5 pasture soils following the single application of 280 kg P/ha or 35 kg P/ha reapplied every 6 months. Soils with low to moderate surface P sorption capacity showed a trend for higher total P concentrations at depth. However, quantitative relationships between vertical P movement and soil properties at depth were poor. A P audit resulted in variable recovery of the applied P (45-128%) in the surface 40 cm at each of the 5 sites. Consistently low P recoveries were achieved at one site, where the surface soil had a high P sorption capacity. Some applied P may have bypassed the high P sorbing surface layers at this site through macropore flow and moved beyond the 40 cm sampling zone, or have been lost to surface runoff. These results question the usefulness of P audit or mass-balance methods for accounting for P movement in a pasture-based system, as spatial heterogeneity of soil properties, both horizontally and vertically, was high in the current study.

Item Type: Article
Authors/Creators:Burkitt, LL and Gourley, CJP and Sale, PWG
Keywords: budget, mass-balance, reapplication, nutrient loss, vertical movement, sorption, buffering, fertiliser
Journal or Publication Title: Australian Journal of Soil Research
ISSN: 0004-9573
DOI / ID Number: 10.1071/SR03025
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