Trials suggest careful VRT approach can lift profitability

Author: Natalie Lee | Date: 01 Jun 2016

Craig Topham taking soil cores for initial soil testing.

Craig Topham, of Agrarian Management, taking soil cores for initial soil testing at Allanooka in April 2015. Extensive soil testing (before sowing) generated information used to develop nutrition strategies for each of the trial sites. Photo by Agrarian Management.

Western Australian research has helped confirm that growers can lift their profitability by varying fertiliser applications within a paddock to more accurately match soil types, yield potential and soil nutritional status.

Trials in WA’s Northern Agricultural Region (NAR) in 2015 showed that gross margins increased by up to $50 per hectare across a paddock when Variable Rate Technology (VRT) was used to vary fertiliser rates in different ‘production zones’, when compared with margins from a traditional non-VRT approach.

Agrarian Management’s Craig Topham and Chris Pinkney conducted the research as part of a Grains Research and Development Corporation (GRDC) Geraldton port zone Regional Cropping Solutions Network (RCSN) project, following a previous similar project which attracted substantial local grower interest.

Mr Topham said trial sites at Allanooka and at Warradarge were zoned into low, medium and high production areas based on soil types – poor pale sand, strong yellow sand and strong sandy gravel – representing the variability in many sandplain paddocks in the region.

“The low production zones had the lowest clay and potassium (K) levels, while the high production zones had the highest percentage of clay and higher K levels,” he said.

The wheat variety Mace was sown on all sites and seasonal fertiliser inputs for phosphorus (P), nitrogen (N) and K were determined for each zone using soil analysis data and in-season Yield Prophet® modelling.

Non-VRT control treatments were determined by using weighted averages of soil analysis data from across the entire paddock and the paddock’s average yield potential.

Mr Topham said birds damaged crops at the Warradarge trial site but meaningful results were achieved at Allanooka despite the very dry season experienced there.

“The targeted nutrition strategy at Allanooka returned a higher gross margin for the low and medium production zones in particular when compared with areas which received the control treatment,” he said.

“But results showed there could potentially be reduced profitability in the high production zones from applying the targeted nutrition strategy and not ‘playing the season’, due to the high cost of inputs in these areas.

“The results highlighted the importance of matching N to seasonal conditions - with the very dry finish to the 2015 season, yields were capped by a lack of finishing rainfall, reducing the response to increased N rates.

“Given the NAR is increasingly experiencing poor finishing conditions, the best strategy for many higher production areas may be to ensure that P and K applications are matched to higher production levels but that conservative amounts of N are applied until later in the season when subsoil moisture levels and yield potential are better understood.”

A man smiling, facing the camera, with silos in the background.

GRDC Western Regional Panel member Paul Kelly says results from a trial in the Geraldton port zone provide some supporting evidence for Variable Rate Technology, which is becoming more common in the WA grainbelt.

GRDC Western Regional Panel member and Mingenew grower Paul Kelly said the results provided supporting evidence for a practice that was becoming increasingly common in the WA grainbelt.

“There is generally enough evidence to suggest that implementing a VRT program is beneficial, although care needs to be taken in choosing the correct strategy for each production zone,” he said.

“The trial results show that to achieve the maximum benefit from implementing a VRT strategy, growers and their advisers must develop a detailed understanding of the variation of their soil nutritional status, key nutrient drivers, and use the latest soil testing and yield predicting methods.”

Mr Kelly said the project addressed a need by growers in the NAR to have increased information about the profitability of VRT, given they faced elevated financial risk due to increased production volatility in an environment of increasing climatic and input cost variability.

Contact Details

For Interviews

Craig Topham, Agrarian Management
0428 645 192

Paul Kelly, GRDC western panel
0427 275 022


Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827

GRDC Project Code AAM0003

Region West