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‘Measure to manage’ nitrogen expenditure in HRZ

TechCrop Services agronomic consultant Jon Midwood, who is national coordinator of the GRDC Hyper Yielding Crops (HYC) initiative, says a 0-30 centimetre-deep soil test will provide growers with a realistic assessment of starting nitrogen, enabling potential input savings.
Photo: GRDC/Dean Allen-Craig

Grain growers in the southern cropping region’s high rainfall zone (HRZ) are urged to undertake critical deep nitrogen soil testing to underpin economically smart fertiliser programs in 2022.

TechCrop Services agronomic consultant Jon Midwood says taking a 0-30 centimetre-deep soil test will provide growers with a realistic assessment of starting nitrogen, enabling potential input savings.

“With input prices at unprecedented levels due to high global energy prices and world events, it is impossible for growers to effectively manage their fertiliser budgets without any measurements in place,” Mr Midwood says.

“If ever there was a year in which growers need to do deep nitrogen testing, it’s this year. Taking a proper 0-30cm deep soil core will give growers an accurate indication of starting nutrient levels.

“Measure to manage is the key phrase for 2022.”

Mr Midwood, who is national coordinator of the GRDC's Hyper Yielding Crops (HYC) initiative and a GRDC Southern Region Panel member, says an accurate assessment of available soil nitrogen could potentially allow for a reduction in planned applications, which may include starter nitrogen, and overall input savings.

Based on the HYC’s Victorian ’top 20 per cent award’ wheat paddocks, which averaged 190 kilograms (units) of nitrogen per hectare in 2020, Mr Midwood calculated that nitrogen expenditure in 2021 would have amounted to about $230/ha.

However, that cost is likely to be upwards of $570/ha in 2022 based on current urea prices at the same application rate.

Prior to this year, four kilograms of grain was generally required to pay for one unit of N (a ratio of 4:1). Even though wheat prices are higher than last year, that ratio has moved to 9:1 based on current prices for urea and wheat.

Market prices of around $800/tonne for wheat and $2000/tonne for canola would be required in 2022 (based on current input costs) to equal the 2021 returns from fertiliser nitrogen.

Mr Midwood says growers will most likely need to consider a new economic optimum for nitrogen when calculating their nutrient needs this year.

“The optimum is the point at which the cost of extra grain produced is not worth the cost of nitrogen that is supplied. Given current fertiliser prices, that economic optimum could require adjustment for 2022.”

Determining the economic optimum for N will require consideration of several factors, including using grain protein levels from previous years as an indication of where growers’ nitrogen management is on a nitrogen response curve.

Mr Midwood suggests growers set realistic production targets in 2022, factoring in paddock history, yield potential in previous years and soil water profile.

“Growers can calculate how much nitrogen they will need and timing of application for the best response by considering their target yield, their starting soil nitrogen levels and where they sit on the response curve if they are to reduce nitrogen inputs,” he says.

Mr Midwood says growers shouldn’t forget the nitrogen available through mineralisation of organic matter if soil conditions are warm and moist.

Mr Midwood says a wheat crop only requires approximately 50kg/ha of nitrogen to carry it to early stem elongation when demand increases significantly. However, in some instances, such as sowing a second cereal or canola after back-to-back cereal rotations, the requirement for early applied nitrogen may be greater.

“The most nitrogen responsive time for wheat, barley and canola is at peak demand which is just prior to stem elongation.

“The least effective time is once plants have passed growth stage 32, and most definitely past GS39. This is when the risk of getting a guaranteed return on a nitrogen application is greatest.”

Mr Midwood’s advice around nitrogen strategies and considerations in 2022 is explained in greater detail in a Southern Farming Systems podcast.

More information on nitrogen use efficiency can be found in GRDC’s A nitrogen reference manual for the southern cropping region.

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