University of Melbourne research has shown nitrification inhibitors, used with standard fertiliser rates, were ineffective in reducing greenhouse gas emissions.
School of Ecosystem and Forest Sciences physiological and ecosystem ecology professor, Dr Stefan Arndt, said it was originally thought fertilisers, containing nitrification inhibitors such as 3,4-dimethylpyrazole phosphate (DMPP) could be very effective in reducing emissions of the greenhouse gas nitrous oxide (N2O).
It was also believed they could increase farm productivity.
"However, these results have mainly been produced in research settings under controlled conditions but were never confirmed in a real farm setting," Dr Arndt said.
The University tested the effectiveness of DMPP on 10 farms in northeastern Victoria over three years.
"It's the first study to do this type of analysis on farm under normal farming conditions," Dr Arndt said.
"Under controlled conditions, we see quite a significant reduction in nitrous oxide.
"Once we went into the field, and this was done over three years in the real world in broadacre and dairy farming, we didn't find any differences at all."
Dr Arndt said that could be related to high fertiliser use.
"If the farmers would use less urea, then you might get benefits," he said.
"Under the high fertiliser regime farmers usually have, under 'business as usual", the DMPP is not going to be very efficient."
He said the use of DMPP did not lead to increased crop yield or pasture production, probably due to high rates of fertiliser application and moist soil conditions during fertiliser application.
He said project's objective was to determine whether it was cost-effective and logistically feasible to reduce on-farm N2O emissions through the nitrification inhibitor amended fertilisers (3,4-dimethylpyrazole phosphate, DMPP or "ENTEC" coated urea).
"Given that DMPP coated fertiliser is significantly more expensive than conventional urea there is little incentive for farmers to invest into nitrification inhibitors," Dr Arndt said.
"It is possible that nitrification inhibitor fertilisers become effective if management practices are altered by applying lower fertiliser rates and different timing of seeding and fertiliser applications, but these will have to be tested under real farm scenarios."
He said it was likely the ineffectiveness of inhibitors was confined to north-eastern Victoria, or regions were the base rate of fertiliser application was high and soils were very wet when fertiliser was applied.
"In agricultural areas where fertiliser application rate is lower and soil moisture is more moderate it is more likely to see a positive effect on reducing emissions and increasing yield," Dr Arndt said.
The on-farm trial had been a useful compromise to incorporate farmer-led management decisions into experimental research on cropping and dairy farming as practised "on the ground".
"We thus advocate for future on-farm trials with DMPP and urea at half the industry's standard fertiliser application rates; a practice that has been shown to maintain and even increase crop and pasture yield in controlled research trials, with the potential of significant cost-savings for farmers," Dr Arndt said.
"Furthermore, DMPP at reduced fertiliser application rates may offer the farmer a further incentive, through potential gains through carbon credits, but this remains to be adequately quantified.
"Under current fertilisation practices, DMPP cannot be recommended as an effective option within GHG abatement programs."
He said the university was very keen to carry out further trials.
"The evidence from research trials in Queensland, suggests if a farmer significantly reduced the amount of fertiliser and use DMPP they would see a benefit.
"The benefit would be financial, the farmer wouldn't use as much fertiliser, so there would be a saving there - the savings would probably outweigh the cost of the inhibitor."
Farmers would continue to make the decisions on when to fertilise and what application rates to use.
"We just mainly run with them and do the monitoring of the productivity of the system and what gas emissions there are," Dr Arndt said.
"Another way of doing this would also be to use a different technology, such as GreenSeeker, with dairy farmers.
The Trimble GreenSeeker crop sensing system helped farmers with managing fertiliser inputs.
"Ideally it would really reduce the cost for farmers, while maintaining productivity and having a significant benefit for the environment," Dr Arndt said.
Researchers were in negotiations with dairy companies and seeking a Federal Smart Farming grant.
"If that funding is granted, we would be carrying out the research in 2018 and subsequent years with dairy farmers."