Nitrogen and disease identified as key constraints to yields

Survey shows two-thirds of wheat paddocks hitting potential

Agronomy
Most wheat crops monitored as part of the National Paddock Survey hit their productive potential. PHOTO Nicole Baxter

Most wheat crops monitored as part of the National Paddock Survey hit their productive potential. PHOTO Nicole Baxter

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Research shows optimising grain production hinges on keeping a range of issues in check.

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A survey of paddocks sown to wheat across Australia shows two-thirds are achieving their attainable yield potential through effective management.

The survey of 250 paddocks was initiated by GRDC to construct a yield-gap calculator to better understand the major yield constraints and improve production.

From 2015 to 2018, CSIRO and Birchip Cropping Group (BCG) researchers - with assistance from other farming systems groups and leading agronomists - have painstakingly recorded crop performance data throughout the cropping cycle.

Lifting performance

CSIRO Agriculture and Food principal research scientist Dr Roger Lawes says a yield-gap calculator identified a lack of nitrogen and disease to be the major wheat yield constraints. PHOTO GRDC

CSIRO Agriculture and Food principal research scientist Dr Roger Lawes says a yield-gap calculator identified a lack of nitrogen and disease to be the major wheat yield constraints. PHOTO GRDC

CSIRO Agriculture and Food principal research scientist Dr Roger Lawes says while the survey results are good news, significant scope exists to improve production on many paddocks.

"The paddocks surveyed were likely to be better performing paddocks from leading grain growers who engaged consultants, agronomists or farming systems group personnel," he says.

"The survey results suggest there's at least one-third of paddocks that fail to reach attainable yields."

When it comes to the key cropping constraints, the research shows 40 per cent of wheat crops surveyed had a nitrogen-limited yield gap of more than 0.46 tonnes per hectare.

Disease pathogens were also an issue, with 48 per cent of wheat crops showing a disease-based yield gap of more than 0.44t/ha.

But these were not isolated causes of low yields.

Dr Lawes says there might be half a dozen problems limiting yields from any one paddock.

The paddocks surveyed were likely to be better performing paddocks from leading grain growers who engaged consultants, agronomists or farming systems group personnel. - CSIRO Agriculture and Food principal research scientist Dr Roger Lawes

Underlying issues

Adequate nitrogen is essential to help wheat crops meet their potential yield. PHOTO Kellie Penfold

Adequate nitrogen is essential to help wheat crops meet their potential yield. PHOTO Kellie Penfold

"In most cases, the yield gap can't be attributed to just one issue," Dr Lawes says.

"Multiple problems are likely, especially if growing wheat after another cereal."

Most of the problems associated with low yields can be tied to crop rotation, Dr Lawes says, with 15 to 30 per cent of wheat crops grown after another cereal.

"In favourable seasons, nitrogen is often the main limiting factor, but some rotation choices can create problems with disease."

Dr Lawes says failure to run a diverse rotation can lead to a spiraling range of problems.

Tactics to improve yields

"When it comes to setting up a wheat crop for optimal yield, the data shows to start with best-practice nutrient management, but also closely look at employing a suitably diverse rotation to minimise disease risks," Dr Lawes says.

"We need to explore whether break crops can be economically introduced into farming systems, as the decision to grow wheat after another cereal might be economically sensible, at least in the short-term."

While the data shows considerable potential for improved crop management, Dr Lawes says it was interesting to note that 66 per cent of paddocks did not have a significant yield gap.

In fact, paddocks surveyed in GRDC's western region had almost no yield gap, on average, in two out of the four years of the study.

For example, during 2018 in Western Australia, there was a small yield gap on average but the variation in the data was significant.

Back then, potential yields were achieved in most areas because of good establishment and adequate winter rain. However, some paddocks became waterlogged, which constrained yield potential.

Across Australia, Dr Lawes says wheat yields ranged from 1t/ha to more than 7t/ha.

"But, concerningly, when yield potential is high, it is often not achieved. What that suggests is that capitalising on favourable seasons is challenging," he says.

He says further work is needed to explore how growers prioritise where to grow their highest-yielding wheat crops.

GRDC Research Code BWD00025

More information: Dr Roger Lawes, 08 9333 6455, roger.lawes@csiro.au

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