FIVE years of research has shown applied nitrogen is less mobile but provides longer term benefits in dryland grain crops than previously accepted in the northern grain region.
It also found timing of application was much less important, upending conventional wisdom that top dressing crops during the season - especially ahead of rain - was the most effective way to ensure they finished well and reached their yield potential.
The latest report from Northern Grower Alliance is based on the results of research trials started a decade ago to investigate whether late application of nitrogen could help boost protein levels and grower returns from EGA Gregory wheat.
NGA chief executive officer Richard Daniel said that research morphed into assessing the impacts of product, timing and different application methods on crop production.
"Invariably, we struggled to show there was any difference in yield, grain quality or economics, whether we applied in January, March, or at planting time," he said.
"We were a little bit surprised how rare it was for timing of application to have an impact. The only time we saw it was at a site that only had 70mm of in-crop rain, with most received just prior to harvest. The nitrogen that went on at planting really had no impact at all, because it sat in the top 1-2cm of soil and was basically stranded and of no benefit to that crop."
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Post-harvest soil sampling at a site which had 300mm of in-crop rain in 2015, showed most of the unused nitrogen was still in the top 10-20cm of the soil profile, when it was expected to have moved down to 30-50cm.
The research focus was broadened In 2016 and 2017 to include detailed assessments of the movement of nitrogen and its impact on following crops.
Data collected from trial sites at Tulloona and Mullaley, NSW, and Macalister and Billa Billa, Queensland, where crops were grown with no added nitrogen fertiliser, showed previously applied nitrogen often took 6-12 months to reach depths of 20-40cm.
"We've all been taught that nitrogen as nitrate is mobile, and it is compared to phosphorus or potassium," Mr Daniel said.
"However, in our dominant cropping soils, vertosols, nitrogen from the original application was still in the top 40-90cm of soil, and providing benefit to subsequent crops, for up to 3-5 years after application."
Mr Daniel said the risk of losses through leaching was minor in a dryland farming situation, on clay soils.
One of the major lessons was that nitrogen fertiliser management should be considered as part of a longer-term strategy rather than an annual tactical decision.
"The relatively slow movement of nitrogen in a dryland system, means farmers trying to run a very extractive system are courting disaster, because once soil nitrogen levels are heavily depleted, it is very difficult to replenish the profile," he said.
"Our fertiliser applications are vitally important, but our work highlighted we get much more crop uptake efficiency from the nitrogen that is already distributed through the soil profile. The goal is to maintain an adequate soil bank of nitrogen which is then regularly topped up to maintain those levels."
The NGA research findings came as no surprise to Paul McNulty, who grows dryland wheat and sorghum at Wondalli, between Goondiwindi and Yelarbon, where average annual rainfall is 606mm and soils are grey cracking loams.
Mr McNulty said most farmers had been conditioned to top dress ahead of rain to avoid losing nitrogen to volatilisation and give crops a boost before grain fill.
"It's a big dollar item," he said.
"We spend more money on urea and phosphorus than we do on our standard fallow spraying of Roundup and the like. It's an amazing amount of money. Obviously if you get it wrong it's going to be bad wrong, it's going to be a big dollar item wrong, and you'll grow a poor crop."
Mr McNulty said he'd been following the NGA research with interest and began applying urea "whenever I felt like it" - usually bringing the contractor in as soon as practical after harvest.
This takes the pressure off both himself and the contractor, whose phone would otherwise be running hot with calls from other clients wanting to spread before rain.
Mr McNulty said he preferred to keep his fields topped up from year to year.
"For the yield expectations that I have, we put 160 kilograms per hectare on what I expect to be a high yielding crop, usually a long fallow paddock, and 120kg/ha on a paddock I don't expect quite so much out of, a short fallow paddock, sorghum, or this year's wheat onto last year's wheat as an example," he said.
"The amount of N that I apply determines my nitrogen response, not whether I apply it before rain or not."
During the drought years of 2018 and 2019, when rainfall at Wondalli dropped to 394mm and 179mm, no crops were planted, and no urea was applied on paddocks.
The 2020 wheat crop drew on the nitrogen reserves from 2017.
"I'm not exaggerating, we got our highest yield ever," he said. "It was not pegged back by lack of nitrogen, even though we hadn't thrown any more out in that year, so I will continue to keep my fields topped up. I want nothing to cap top end yields in the good years."