Targeted lime applications will deliver higher long term yield benefit than phosphorus fertiliser on many Western Australian cropping paddocks according to recent monitoring by the Department of Agriculture and Food.
Department development officer Greg Shea said the results showed that most cropping paddocks had sufficient phosphorus levels, while more than three quarters of paddocks surveyed had low pH levels limiting grain yield potential.
“With many paddocks unlikely to respond to phosphorus, growers have an opportunity to divert some of the money they might spend on phosphorus fertiliser into lime applications on targeted areas of the farm,” Mr Shea said.
Growers can save about $15/ha by not applying standard phosphorus rates on paddocks with already healthy levels.
“The savings from that part of the cropping program will make inroads into the cost of 2.5 tonne/ha of good quality lime which is a commonly recommended rate in the Wheatbelt,” Mr Shea said.
About 67 per cent of the 184 paddocks surveyed (between Yuna and Jerramungup) had a pH less than 5.5 in the top 0-10cm of soil.
“A pH of less than 4.8 in the topsoil can prune roots of crops such that they can’t explore the soil for water and nutrients, and are more dependent on fertiliser. This is the situation where phosphorus rates should not be cut,” Mr Shea said.
“Once the topsoil drops below pH 5.5 crop yields are compromised and only liming can bring these soils back towards their yield potential.”
Mr Shea encouraged growers to monitor soil pH and identify priority areas for targeted lime applications as a third of the surveyed paddocks also had a subsoil pH below the critical level of 4.8.
“It is better to apply more lime to priority areas than a lower rate across whole paddocks,” said Mr Shea.
While the survey indicated most paddocks are unlikely to respond to phosphorus fertiliser, Mr Shea said factors such as soil water repellence and acidity can increase fertiliser phosphorus requirements of crops due to root growth being constrained.
The monitoring has confirmed the results recently published in the Report Card for Sustainable Natural Resource Use in Agriculture.
The soil acidity data was collected by a collaborative project between the department and Precision SoilTech with funding by the Australian Government’s Caring for our Country.
The monitoring formed part of the Focus Paddock project co-funded with the Grains Research Development and Corporation.
For more information on the phosphorus status of their soils, growers can use their own soil test results with the online tool found at agric.wa.gov.au/pmodel
It is recommended that growers seek the advice of independent agronomists to finetune their fertiliser and liming plans.
Media contact: Jodie Thomson/Lisa Bertram, Media Liaison +61 (0)8 9368 3937