Phosphorus: fluid or granules?

By Mike McLaughlin

Fluid phosphorus (P) fertilisers have been found to be very effective on alkaline calcareous soils in southern Australia, such as those found on Eyre Peninsula, York Peninsula and the Mallee.

A collaborative project between the university of Adelaide (Mike McLaughlin, Therese McBeath), NSW Department of Primary industries (Mark Conyers), Department of Agriculture WA (Mike Bolland), South Australian Research and Development institute (Bob Holloway), and CSIRO Land and Water (Enzo Lombi) is examining whether fluid fertilisers offer significant advantages over granular products in a wider range of acidic and neutral soils from several states around Australia. The Queensland Department of Primary industries and Fisheries (Mike Bell) and the Victorian Department of Primary Industries (Roger Armstrong) are also collaborating with the project team.

The project has a two-phase work program in which the first phase is initial screening of crop response to granular and fluid fertilisers on a wide range of soil types under glasshouse conditions.

Fluid fertilisers assessed were liquid monoammonium phosphate (Liq-MAP) and ammonium polyphosphate (APP) and the granular "control" treatment was monoammonium phosphate (Gran-MAP).

The project team collected 29 phosphorus-deficient acidic and neutral soils from Wa, SA, Victoria, NSW and Queensland and these are being fully characterised in terms of soil physical and chemical characteristics. The laboratory/glasshouse evaluation used wheat as The test plant, with early plant growth and phosphorus uptake assessed. This phase is almost complete, with plant and soil materials currently being analysed.

Initial results suggest that some acidic and neutral soils may also respond significantly to fluid P fertilisers (response as measured against the same amount of phosphorus supplied as traditional granular products such as gran-MAP). responses with fluid fertilisers were not as spectacular as those generally found previously on highly calcareous soils, but were still significant - up to 35 per cent greater growth than those with granular P fertiliser - in 25 per cent of the soils tested.

The interim results suggest that it is worthwhile evaluating fluid fertilisers on a wider range of soil types in higher-rainfall grain production areas where acidic and neutral soils predominate. If these interim results stand when the analyses are completed, the project will move into its second phase of testing fluid forms of phosphorus against granular under field conditions.

Mike McLaughlin is a Professor in Earth and Environmental Sciences, University of Adelaide.

GRDC Research Code UA00081

For more information: Mike Mclaughlin,

Region North