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

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journal contribution
posted on 2023-05-16, 13:43 authored by Burkitt, LL, Gourley, CJP, Sale, PWG
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.

History

Publication title

Australian Journal of Soil Research

Volume

42

Pagination

89-98

ISSN

0004-9573

Department/School

Tasmanian Institute of Agriculture (TIA)

Publisher

CSIRO Publishing

Place of publication

Collingwood, Melbourne, Victoria

Repository Status

  • Restricted

Socio-economic Objectives

Dairy cattle

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