By David Horwood
For the majority of Australian graingrowers, fluid fertilisers will not improve yields or offer other advantages that are financially viable, a GRDC study has concluded. But the study does recognise that fluid fertilisers have a place in some circumstances.
Dr Peter Wylie, of Horizon Rural Management in Dalby, Queensland, led the team that compiled the GRDC report.
On the evidence to date, the report says, most Australian cropping soils will not show improved crop yields or better fertiliser efficiency from applications of fluid phosphorus fertiliser. Gains will most likely be restricted to soils where there are limitations to phosphorus availability.
Dr Wylie says one striking example of fluid fertilisers is on the Eyre Peninsula, where farmers are applying lower rates of phosphorus in a fluid form, yet achieving better yields.
On these soils it is possible to make money with fluid phosphorus fertilisers, despite the higher costs. It appears that on highly calcareous, alkaline soils, phosphorus added as granular fertiliser is quickly precipitated as insoluble calcium phosphates, which are not available to plants. Fluid phosphorus fertiliser is better distributed and may remain in solution for longer, with less fixation into insoluble forms.
The report estimates there could be as many as 3000 farms in southern Australia growing almost two million hectares of crop that could benefit from fluid phosphorus fertiliser. However, at present only around 80 farmers use fluid phosphorus for some or all of their fertiliser requirements.
"More research is needed to identify the full extent of responsive soils and predict when growers can expect a financial benefit from fluid phosphorus," Dr Wylie says.
"Some soils of the Victorian Mallee might respond. A small part of WA also has highly calcareous soils. And there are some acid soils with high iron or aluminium levels which immobilise phosphate and may respond to fluid forms of phosphorus fertiliser."
The most promising development in reducing the cost of fluid phosphorus fertiliser is suspensions of fine grades of MAP (Monoammonium phosphate) or DAP (Diammonium phosphate). Slurry blends are likely in the future with different forms of phosphorus, such as MAP and phosphoric acid.
On fluid nitrogen fertilisers, the report is cautious. Use of fluid nitrogen is increasing, particularly in WA, driven by convenience and greater flexibility, especially with the move to post-emergence nitrogen application.
However, the report says farmers need to examine their situation carefully. "It is difficult to justify the extra cost of fluid nitrogen fertiliser on convenience grounds, because the additional cost of using fluid nitrogen could amount to $15,000 on a typical farm with 1000ha of crop."
For further information:
Dr Peter Wylie, 07 4662 4899, firstname.lastname@example.org
The full report, The potential of fluid fertilisers for broadacre cropping in Australia, can be found on the GRDC website at http://www.grdc.com.au/growers/res_summ/HOR00002/intro..htm
GRDC Research Code: HOR 00006, program 4