Stratification, forms, and mobility of phosphorus in the topsoil of a Chromosol used for dairying

Level 1 General description


The purpose of this study was to investigate the forms and stratification of soil phosphorus (P) and their relationship to mobile forms of P in soils collected from a subcatchment used for grazing of dairy cattle in the Adelaide Hills, South Australia.

Methods (brief)

Composite soil samples were collected from a 2.5 ha subcatchment that has been used for dairying for > 30 years. Soil samples were analysed for CaCl2-extractable P. Twelve re-packed soil trays comprising a subset of the soils were constructed to examine the relationship between the concentrations and forms of P in soil and runoff.

The trays were sown to ryegrass (Lolium perenne) and grown in a glasshouse for 4 months prior to the rainfall simulation experiments. Rainfall simulations were undertaken with an application rate of 30 mm/h over an average 30 minute period. A subsample of the runoff was then collected for filtration and analysis.

Key findings (brief)

Phosphorus in the soils was highly stratified. The concentration of calcium chloride extractable P in the 0–0.01m increment was, on average, 5.7 times greater than in the 0.05–0.10m increment. Organic P (% of total P) in the top 0.01m was significantly (P<0.001) related to soil P content such that low P soils (total P of ~600 mg/kg) had high proportions of Po (~65%),whereas high P soils (total P of ~2000 mg/kg) had low proportions (~25%) of Po.

Runoff P from the soils was predominantly (86%) dissolved. The dominant process of P mobilisation from high P soil was dissolution of phosphate (reactive P), whereas from a low P soil, the mobilisation of reactive and unreactive P was of similar importance.


Flaxley Agricultural Research Centre, Adelaide Hills, South Australia.

Related studies


Key references and sources of this data synthesis

These data summaries have been extracted from

      i. Dougherty WJ, Nash DM, Chittleborough DJ, Cox JW, Fleming NK. 2006. Stratification, forms, and mobility of phosphorus in the topsoil of a Chromosol used for dairying. Australian Journal of Soil Research 44: 277 – 284.