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There is a high degree of inbuilt fertility in irrigated soils, nitrogen use efficiency research has shown.
Photo: courtesy Ben Morris

Nitrogen use efficiency trials as part of the wider ‘Optimising Irrigated Grains’ (OIG) project showed that irrigated farming systems have inherent fertility levels. In some cases, relatively good yields were achieved with no added nitrogen.

Irrigation Farmers Network trials manager Damian Jones says this is seen at Kerang in Victoria, where canola yielded three tonnes per hectare and maize 10t/ha with no added fertiliser.

Irrigation gives us a wider window of opportunity to top-dress our crops and access more nutrients later in the season if we need to.

Field Applied Research (FAR) Australia managing director and lead researcher Nick Poole agrees and says that a wider window and potential later application fits well with durum production. “This is where later applications (at flag leaf emergence) give a good combination of both yield effect and protein.”

The project saw trials on six crops take place at two Irrigated Research Centres – Kerang in Victoria and Finley in southern NSW. The GRDC-supported research set out to identify gaps in knowledge about irrigation potential among grain maize, barley, canola, chickpeas, durum and faba beans.

As well as inherent soil fertility, the researchers found a nitrogen application ceiling.

Mr Jones says that two different sites across three years showed a consistent lack of crop response when application rates were higher than 250 kilograms of nitrogen/ha. “I hope growers look at these results when they make their nitrogen decisions rather than simply pile on more urea based on the theory that if some is good, then a lot more must be better.”

Mr Poole agrees. “We know that grain maize crops yielding 16 to 20t/ha remove approximately 400kg of nitrogen/ha, but we couldn’t get them to respond significantly  and economically in that season to more
than 250kg of nitrogen.

“Where you have fertile farming  systems where nitrogen is reintroduced to the rotation by legume or pasture legumes, it was clear that all crops benefited from considerable nitrogen mineralisation that supports the remainder of the nitrogen requirement. However, with summer crops the benefits appear to be greater, since soils are warmer.”

More information: Nick Poole,; Damian Jones,

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