Few growers currently conduct nutrient testing in the sub-soil, instead focussing on the topsoil.
The Grains Research and Development Corporation (GRDC) supported research is being conducted in WA by Murdoch University, CSIRO and the Department of Agriculture and Food (DAFWA).
It has shown that, in many circumstances, nitrate stored in the sub-soil is available to crop roots.
Project leader Richard Bell, Professor in Sustainable Land Management at Murdoch University, said this meant many growers could potentially reduce nitrogen fertiliser rates and applications.
“Situations where subsoil nitrates are available to crops include heavier textured soils and drier seasons when nitrates are unlikely to leach away before roots can reach them,” he said.
“However, access to subsoil nitrates by crop roots can be reduced by soil constraints such as hardpans or aluminium toxicity.”
Researcher Mike Wong, of CSIRO said the project had also revealed that, even in higher rainfall areas, acidic sub-soils were more likely to retain nitrates, which could then be accessed by plant roots.
Previously it was believed that nitrates leached freely from all soils.
“A simple way to determine potential sub-soil nitrate retention is for growers to conduct sub-soil testing for sulphates, because adequate sulphate levels are an indicator of nitrate retention,” Dr Wong said.
Researcher Yvette Oliver, of CSIRO, said the new information generated by the GRDC project about nitrates in the sub-soil highlighted the importance of growers conducting nutrient sub-soil testing.
“They can use that information and adjust their nitrogen fertiliser programs accordingly, potentially cutting back on costly nitrogen applications and increasing profits,” Dr Oliver said.
The research project is continuing and aims to better understand the circumstances where sub-soil nitrates are of most benefit to crops.
It was instigated under the GRDC’s ‘More Profit from Crop Nutrition’ initiative which aims to help grain growers achieve efficient and profitable fertiliser practices.
Some of the findings from the initiative are outlined in articles contained in the GRDC Ground Cover More Profit from Nutrition Supplement at www.grdc.com.au/Ground-Cover-97-Supplement
The GRDC is continuing its nationally co-ordinated systems approach to nutrition research and extension under the ‘More Profit from Crop Nutrition II’ initiative.
Research under the new initiative will focus particularly on matching inputs to crop demand and there will be an emphasis on providing growers with information to help them make effective fertiliser decisions.