Applying the fertiliser sulphate of ammonia onto a paddock that has recently been limed may increase soil nitrogen losses through volatilisation – meaning less nutrients for crops and potentially higher input costs for growers – new research shows.
Led by the University of Western Australia (UWA), the research is part of a Grains Research and Development Corporation (GRDC) investment that aims to help growers with their fertiliser decisions to increase crop productivity and improve nitrogen fertiliser use efficiency.
The 14-month project is being led by UWA School of Agriculture and Environment Associate Professor Louise Barton, with a research team including UWA scientists Professor Zed Rengel, Dr Fiona Dempster, Paul Damon and Associate Professor Matthias Leopold, as well as Murdoch University’s Professor Daniel Murphy.
The multidisciplinary team includes members of the Soils West alliance, The UWA Institute of Agriculture and UWA Centre for Agricultural Economics and Development.
According to agronomists surveyed as part of the project, the application of lime and sulphate of ammonia in WA occurs but is not widespread.
Growers who employ the practice are utilising it mostly on sandy soils around once every three to six years. Traditionally, sulphate of ammonia has been used in farming systems with these types of soils to both provide nitrogen and to meet the sulphur requirements for sowing canola.
Project lead UWA Associate Professor Louise Barton says that growers should be aware that sulphate of ammonia applied onto the surface of recently limed soils risks being volatilised, particularly if there is insufficient follow-up rain to move the sulphate of ammonia below the surface of the soil.
“The project’s first glasshouse study investigated potential volatilisation losses from surface applications of lime and sulphate of ammonia to a dry soil prior to seeding, and in response to different simulated rainfall scenarios afterwards,” Assoc Prof Barton says.
“Losses after three weeks ranged from less than one to 20 per cent of the nitrogen applied.
“The greatest losses occurred from the limed soils under a ‘low’ break-of-season rainfall, with losses more than halved under a ‘high’ break-of-season rainfall scenario.”
In addition, Assoc Prof Barton says that applying ammonium sulphate onto a dry soil prior to sowing a second crop that contained residual lime from the first glasshouse study also produced a risk of volatilisation.
“A second glasshouse study investigated if residual lime remaining in the surface soil after growing a canola crop through to maturity also promoted ammonia volatilisation. In this study, losses ranged from less than one to 25 per cent of the nitrogen applied,” Assoc Prof Barton says.
The project, which is now nearing completion of its second phase, included a scientific review and agronomist survey as well as a series of glasshouse studies investigating the short and medium-term interactions between soil type, liming, and application of sulphate of ammonia on ammonia volatilisation losses, crop growth and grain yield.
GRDC Sustainable Cropping Solutions Manager – West, Rowan Maddern, says the project is providing new and quantitative data for WA growers to help with their fertiliser and liming decisions.
“Given the increasing reliance on nitrogen fertilisers in WA, and greenhouse gas emissions associated with their production and use, understanding whether this is a significant loss pathway is important,” Dr Maddern says.
“Growers should consider these initial findings when applying lime and sulphate of ammonia in their nutrition programs.
“Think about applying them in different years, not immediately after each other in the same spot.”
The final step in the study is to assess if the loss of nitrogen fertiliser from ammonia volatilisation prior to seeding impacts the growth and yield of crops grown in each glasshouse study.
Full project results are expected to be presented to WA growers at the upcoming GRDC Grains Research Update, held in Perth on 27 and 28 February.