After several decades of no-till and precision farming in Western Australia’s grain growing regions, new research is attempting to discover what happens to soil nutrients under these new farming regimes.

In this three part series, GroundCover reporter Jo Fulwood outlines early findings from a major new research focus in GRDC’s western region looking at soil nutrition, the effects of amelioration on nutrient availability and new soil testing procedures to more accurately understand soil nutrition levels.

A major new research project is attempting to better understand the complex science behind interactions between agronomic management and nutrient availability in the soil.

Changes over the past few decades to Western Australian farming systems have led researchers to reassess how well current approaches estimate soil nutrient supply to crops.

The University of Western Australia project, led by adjunct research fellow Dr Craig Scanlan as a part of the SoilsWest alliance, is just one of three major new projects on soil nutrition.

Dr Scanlan, who is also a research officer at the Department of Primary Industries and Regional Development (DPIRD), says the GRDC-invested project is a huge step forward in the quest to gain a better understanding of soil nutrient supply in current farming systems.

The project combines field trials, glasshouse research, laboratory research and economic modelling, and includes partners from Murdoch University, the University of Adelaide, the Southern Dirt grower group, Equii Consultants, CSBP and Summit.

The project includes:

• Long-term trials that study the cumulative effects of crop sequence, soil management and the rate of applied phosphorus or potassium on grain yield;
• Field trials that examine how crop residues and fertiliser placement influence the yield response to nitrogen or phosphorus fertiliser;
• A series of annual trials in collaboration with CSBP and Summit aimed at gaining a better understanding of how soil properties and climate influence the wheat yield response to phosphorus fertiliser;
• Laboratory work that will quantify the different forms of phosphorus in WA soils; and
• Research that fills some knowledge gaps on nitrogen processes in the soil that will deliver better predictions of soil nitrogen supply.

Dr Scanlan says what is happening beneath the soil surface, particularly after many years of no-till and precision farming, needs further investigation to ensure growers are maximising profits from applied fertiliser.

"Given the amount of variable costs spent on fertilisers, it's critical that growers and advisers have all the required information to allow them to make informed decisions," he says.

"The aim of this research is for growers to achieve more profit from their investment in fertiliser."

Dr Scanlan says fertiliser requirements are driven by the gap between demand by the crop and supply from soil and residues.

Predicting soil nutrient supply based on previous research has become more difficult as our farming systems change, he says.

Current research is investigating the potassium supply from a wide range of soil types, with the aim of testing whether predictions based on current soil testing methods are appropriate for all soil types.

Importantly, this work will provide the evidence for improved soil testing methods for medium and heavy soils.

Supporting fertiliser decisions

Dr Scanlan says this research on soil testing for potassium is one example of how the outcomes from this project will help growers make fertiliser decisions.

"The models used to predict fertiliser potassium requirements are built mostly on data from sandy soils that have low native potassium and low capacity to store potassium," he says.

"It is likely that soil potassium supply is being run down in other soil types also, due to the cumulative effect of removing the potassium in grain or hay over decades of farming."

The project has a broad scope; it includes research work at a very small scale in the laboratory, right through to field trials.

Dr Scanlan says the overlap in scales of research completed in the project will lead to a better understanding of soil supply of nitrogen, phosphorus and potassium.

"Our aim is to bring together the knowledge we gain on processes that are driving nitrogen, phosphorus or potassium supply in soils, with the results from our field experiments providing growers and consultants with the information they need to tailor fertiliser inputs," he says.

Collaborative effort

Another important outcome from the project has been the rebuilding of the group of researchers working in nutrient management in WA.

"As part of the project, a research fellow from UWA, plus two PhD students, one from UWA and one from Murdoch, have been appointed, which will increase the skills and knowledge available to allow the industry to better respond to some of the problems we face in nutrient management in the western region," Dr Scanlan says.

The project began in early 2018 with trials right across WA's grain growing region.

Further research is underway considering the impact of amelioration on nutrition availability and developing improved soil testing guidelines.

More information: Dr Craig Scanlan, craig.scanlan@dpird.wa.gov.au