Wednesday, October 5, 2022

Capping nitrogen for export hay quality

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Department of Primary Industries and Regions (PIRSA) (South Australia), Media Release, 12 July 2021

More nitrogen isn’t always better – especially in a drier year – when producing quality hay is the key to farm returns.

That’s according to research funded by AgriFutures Export Fodder Program as part of the National Hay Agronomy (NHA) Project.

Dr Courtney Peirce, a Senior Research Officer at the South Australian Research and Development Research Institute (SARDI), who led the South Australian component of the NHA project said the research findings suggested growers wouldn’t be disadvantaged by a conservative nitrogen application strategy in drier growing seasons.

“The field trials at Hart during the past two seasons mostly produced high quality hay”, she said.

“The exception were the trials that were under severe nitrogen stress, but overall, the oaten hay quality and yield did not suffer from a conservative approach to applying nitrogen.”

“If your focus is on hay quality, then you don’t want to apply too much nitrogen as higher nitrogen rates can result in lower water-soluble carbohydrates (WSC) and higher fibre content – such as acid detergent fibre and neutral detergent fibre – increasing the likelihood of downgrades in hay quality.”

Export hay trials in 2020, at Hart in South Australia demonstrated no benefit when applying more than 30kg N/ha because of the dry winter, but higher applications were more profitable in the Victorian Wimmera due to more consistent rainfall during winter and early spring allowing plant uptake of nitrogen.

The “sweet spot” for nitrogen applications strikes the balance between quality and quantity in export hay crops and it’s determined each year by the season.

Although weather forecasts for South Australia and Victoria remain variable, Courtney said the research showed more conservative nitrogen applications were best for hay crops after a dry season start.

“This season in many parts of South Australia, there has been limited rainfall, with the moderate season break occurring in late May,” she said. “The growing season rainfall will determine how much applied nitrogen can be taken up by the crop, and our trials suggest that a conservative approach is most likely to be the best-bet.”

“Even if we get above average rainfall for the rest of the season, resulting in increased nitrogen mineralization, you could end up with poorer quality hay because of the timing of when the nitrogen becomes available. Applying nitrogen too late causes it to accumulate as nitrates in the plant.”

The nitrogen strategy for the NHA trials includes top-dressing two-thirds at seeding and one third six weeks after germination, with the final nitrogen application applied mid-tillering.

“By this mid-tillering stage in the growing season, it is hoped that the weather forecasting and known plant available soil water enables the grower to decide if the second nitrogen application is still necessary,” Courtney said. “If the yield potential has decreased for the hay crop, then this application may be dropped.”

NHA project manager Georgie Troup said most export fodder crops throughout Australia require 30- 90kg N/ha, depending on the yield potential and growing season.

A trial in Western Australia last year demonstrated a yield increase for an April-sown crop with applications up to 150kg N/ha, but this was detrimental to quality. The “sweet spot” was 90kg N/ha as this produced 8 tonnes/ha with 25.4 per cent WSC. and was top grade export oaten hay.

As soon as you apply nitrogen there’s a gradual decline in WSC, so it is about finding the point where you optimise yield without having an effect on hay grade and profitability,” Georgie said.

Other research by the NHA project showed no gain if gibberellic acid is applied to export hay crops to increase head emergence in lower rainfall areas. The NHA team assessed if gibberellic acid could be used to improve the likelihood of head emergence from the boot.

The head getting ‘stuck’ in the boot causes frustration for many growers when there’s warm and dry conditions in spring. This issue with head emergence has been linked with moisture pockets within the windrow and bale and could lead to haystack fires if effective crushing and drying of the head cannot be achieved.

Gibberellic acid has been proven to assist in boosting production for other agricultural crops, and while it did show signs of increasing the height of oaten hay plants, it didn’t assist with increasing the head emergence from the boot.

“Last year was the ideal scenario for us to trial gibberellic acid, there were two trials in Western Australia, at Wongan Hills and Merredin, both were under moisture stress from mid-season, and it was a tight finish to the growing season,” Georgie said.

“If the gibberellic acid was going to be useful, it would have been apparent there in 2020. But only one variety was able to fully emerge from the boot, and it was the short season variety Durack, which had a maturity advantage over the longer season varieties.”

The National Hay Agronomy (NHA) project is a four-year investment by the AgriFutures Export Fodder Program and aims to address current knowledge gaps in the Australian export fodder industry.

For more information on the program and research visit www.agrifutures.com.au

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