AUSTRALIAN farmers spend almost $500 million a year on nitrogen fertiliser which apparently never delivers a cropping advantage.
At the same time the rest of the world is gaining greater productivity results from rising fertiliser use, Australian crop production has basically plateaued.
That is despite Australian farm increasing nitrogen use by 65 per cent between 2010 and 2015.
Queensland University of Technology's (QUT), Professor Peter Grace, has calculated about 39pc of the nitrogen applied as synthetic fertiliser to crops in 2015 was lost from the soil as a result of increasing natural leakage issues ranging from atmospheric losses to rainfall runoff.
That loss was worth about $475 million in wasted input value in 2015, of which about $326m (or 37pc) was lost by the grain sector.
Percentage losses were even higher - between 40pc and 65pc - for the horticulture, cotton and sugar industries.
Although global nitrogen fertiliser prices have actually halved since 2012, triggering a significant lift in affordability and local fertiliser usage, Professor Grace said Australian farmers had not necessarily gained much benefit from cheaper inputs.
Australian crop productivity only lifted about 9pc in the first five years of this decade to about 79 million tonnes.
Global crop productivity rose almost 10pc in the same period, but unlike Australia which had significantly pumped up its nitrogen applications of late, global nitrogen usage was only up about 10pc.
Australian farmers' nitrogen habit has been at unprecedented highs since 2011, with about 1.4m tonnes of nitrogen applied in the lead up to the 2015-16 winter crop harvest (about 200,000t of which was also spread on grazing pastures).
At an average price of about $1000/t, Australia's nitrogen fertiliser bill in 2015 totalled about $1.4 billion.
Between 2007 and 2010 Australian nitrogen usage was less than 700,000t annually.
Record high fertiliser costs and drought were likely factors behind the restrained use in that period.
Professor Grace said even when usage peaked in Australia early last decade, farmers only applied about 850,000t of nitrogen a year, and prior to that volumes were down around 600,000t mark.
While the 2016 winter crop harvest is still rolling in and yet to be tallied against nitrogen applications last season, he said it was clear Australian fertiliser applications were struggling to stay useful in our cropping soils.
He said Australia's already aged soil profiles were generally not as rich in organic matter as they may have been 40 years ago and after decades of cropping activity "don't have enough body" to retain big booster shots of synthetic nutrients.
Professor Grace said ideally smaller, but more regular nutrient applications were needed during the season to make nitrogen usage more efficient, particularly prior to, and during planting.
However he acknowledged "that's easier said than done", especially as crops grew taller and more difficult to manage with fertiliser machinery.
Depending on the soil types involved, a considerable amount of applied nitrogen was being lost through leaching, or released and washed off in rainfall and paddock flooding.
About 1pc of atmospheric nitrogen losses were released as nitrous oxide emissions - most notably from sugar cane farms - which damage the earth's ozone layer.
"One of the solutions to improve nitrogen use efficiency is to be more proactive about building soil organic matter, including not burning crop stubble residues, where possible," he said.
"Growing legume crops to naturally build soil nitrogen via a slow release process is also important."
Professor Grace said most soils were not capable of absorbing and holding "a big whack" of nitrogen in one or two shots, especially if a storm delivered a rainfall downpour soon after application.
This had become more relevant today because much of Australia's cropping country had been effectively "mined" of its productive capacity between the 1950s and 1980s and now required more man-made inputs to help make up the difference.
"Increasing nitrogen usage efficiency will be a win-win for production and the environment," he said.
"We need to get better at understanding seasonal weather outlooks and matching our initial nitrogen applications with demand, especially if the season is starting out dry.
"Irrigated crops ideally need to have a regime of less water, more often.
"Grain legumes and cover crops also have to be a priority to build soil nutrition and organic matter."