A series of 15 research trials conducted by the Grains Research and Development Corporation (GRDC) funded Northern Grower Alliance (NGA) over the past three years found that the rate of N applied was consistently the dominant factor affecting yield, grain quality and economic returns.

One aspect of the research compared the impact of urea incorporation compared to surface spreading alone.

The results support the volatilisation work done by NSW Department of Primary Industries senior research scientist Dr Graeme Schwenke, which indicated that the volatilisation losses from surface applied urea were frequently much lower than previously expected.

NGA chief executive officer Richard Daniel said the trial work consistently showed equivalent crop responses in terms of biomass, yield and grain quality from urea spread immediately post sowing, and with no physical incorporation, compared to the same rate of urea spread and incorporated by sowing.

“All sites were nitrogen responsive, with significant grain protein responses to nitrogen rate in all trials,” Mr Daniel said. “That is not to say we aren’t losing ‘a quantity’ of N via volatilisation. It is indicating the levels of loss have been low and not sufficient to measure any difference in crop performance.”

In Queensland and NSW, growers typically apply nitrogen fertilisers such as urea directly into the soil (banding) or broadcast it on the surface then incorporate.

This is done to reduce the potential for ammonium containing or ammonium producing fertilisers volatilising into the atmosphere as the gas ammonia.

A range of N application timings were also evaluated as part of the research. A split application of N (50 per cent incorporated at sowing and 50 per cent spread at ~GS30) was evaluated in all trials, while early and late fallow applications were included in 2015 and 2016.

Split applications of N performed more consistently than expected and provided equivalent crop responses to the same total quantity of N applied at sowing.

The results confirm that in-crop spreading can be a useful tool to capture upsides in yield and grain quality when seasons are favourable however the practice is unlikely to become standard practice in the north due to the variable nature of late winter and spring rainfall.

Fallow N applications were evaluated in 2015 and 2016 and have generally provided equivalent results to the same quantity of N applied at sowing.

In trials where differences were evident, Mr Daniel said the impact appeared to be linked to other agronomic issues such as seedbed soil moisture disturbance (negative impact on establishment and yield) or breaking up of high stubble loads prior to planting (positive impact).

“A large focus of this work was to examine whether adjusting timing (or method) of N application could assist in the management of wheat varieties with low protein achievement,” Mr Daniel said.

“Unfortunately the conclusions to date are that these tools are of minor impact with N rate the key driver. The work however has also helped to generate a large trial data set that indicates the losses from surface spread urea are much lower than previously expected.

“If there is one message to stress from this work, it is to keep N application simple. The benefits from adjusting timing and method appear relatively minor and growers may be better off applying when and where it suits other operations. Getting the N rate right appears much more important than timing or method.”