Avoiding frost losses in wheat

Variety research results can help with 2019 frost planning

Frost Management
GRDC research investments are showing fast-growing winter wheat varieties and new agronomy management packages can help manage risks of frost, heat and water stress. PHOTO GRDC

GRDC research investments are showing fast-growing winter wheat varieties and new agronomy management packages can help manage risks of frost, heat and water stress. PHOTO GRDC


Fast-growing winter wheats are helping growers tackle seasonal variability.


Early results from GRDC research investments show fast-growing winter wheat varieties and new agronomy management packages have the potential to help growers minimise losses from damaging frost, heat and water stress.

A recent study highlights the need for new fast winter wheats with stable flowering dates to help growers combat seasonal variability and exploit very early sowing opportunities.

Having this information about flowering helps GRDC focus its investment planning on better varieties and yield outcomes for growers, says John Rochecouste, GRDC Manager Agronomy, Soils and Farming Systems North.

The work, by GRDC-supported PhD student Bonnie Flohr, shows wheats that flower outside the optimal period are likely to produce lower-than-average yields because of greater risks of frost, heat and water stress.

Ms Flohr says April/May planting rain has declined since 1996 most severely during the Millennium Drought when wheat crops that did establish after a dry autumn flowered too late to cope with the dry spring.

Over the same period, Australian wheat breeders focused on cultivars with increasingly rapid development to suit those short seasons, and largely ignored slow-developing varieties, particularly winter wheats, she said.

Flowering time

Ms Flohr said flowering time is one of the main drivers of grain yield and quality. But until recently the optimum flowering time has been unknown for many locations in southern Australia.

In consequence, one of the first tasks of Ms Flohrs PhD study, supervised by La Trobe Universitys Dr James Hunt, CSIROs Dr John Kirkegaard and the ANUs Professor John Evans, was to identify the optimal periods during which wheat must flower in south-east Australia for yield to be maximised.

Having this information about flowering helps GRDC focus its investment planning on better varieties and yield outcomes for growers. - GRDC Manager Agronomy, Soils and Farming Systems North John Rochecouste

Ms Flohr said other researchers had defined the optimal flowering period as the time from the last spring frost to before the onset of heat stress. However, she said this definition ignored the critical role water supply and demand plays in defining the optimum flowering periods for different locations.

Using the widely validated crop simulator Agricultural Production Systems sIMulator (APSIM) to combine the effects of historic climate records, biomass accumulation, water use and temperature, Ms Flohr defined the optimum flowering period for 28 sites across south-east Australia.

Simulated crops were sown weekly from April 1 to July 15 of each year. The relationship between flowering date and grain yield was established using climate records from 1963 to 2013.

The optimal flowering periods for wheat varied with site and season and were differentially driven by seasonal water supply and demand and extremes of temperature, depending on the site, Ms Flohr said.

To evaluate this further, she established a two-year trial near Temora, NSW, during 2015 and 2016 in which she planted 18 wheat cultivars at four different sowing dates from mid-April to mid-May.

She planted a mid-winter wheat (EGA Wedgetail), a fast winter wheat (a new Australian Grain Technologies cultivar, Longsword), a mid-spring wheat (EGA Gregory) and a fast spring wheat (Condo), as well as a range of historical wheats.

The four sowing dates in 2015 were April 17; April 27; May 7 and May 15. In 2016, the sowing dates were April 14; April 26; May 6 and May 15.

Fertilisers and pesticides were applied such that nutrient limitations, weeds, pests or diseases did not limit yield.

Flowering time was recorded as the time when 50 per cent of the heads in each plot had visible anthers, and was expressed as thermal time the sum of daily average temperatures between sowing and flowering.

A mean flowering stability index was calculated by dividing the thermal time range in flowering for each cultivar by the thermal time range in sowing dates for each year.

Putting it together

Ms Flohr said the yields of the AGT Longsword were competitive with those of the fast spring wheat Condo sown at their optimal sowing dates.

This is partly because it has vernalisation genes (a requirement for a cold period) to control its development in the environment.

Having access to fast winter wheats which are more likely to flower within the optimal window from a broad range of sowing dates in different environments would help maintain yields and minimise damage from frost, heat and water stress, she said.

There is strong evidence that wheat breeders should consider releasing new winter wheats that are more adapted to a broad range of sowing dates.

New investment tackles irrigation challenges

A new suite of GRDC investments is investigating existing and novel soil management technologies to improve soil structure, infiltration and moisture retention in modern irrigation systems.

The projects will support irrigated growers in their efforts to increase profitability from their cropping systems, particularly on shallow and poorly structured red duplex soils and sodic grey clays prone to dispersion and waterlogging.

GRDC Senior Manager- Grower extension and communication, Luke Gaynor says the new investments are designed to provide irrigated grain growers with the knowledge, confidence and tools to adopt management strategies which optimise return on investment.

About 0.40 million hectares of poorly structured grey sodic clay soils and approximately 0.75 million ha of shallow transitional red brown earths exist under irrigation in the southern Murray Darling Basin, Mr Gaynor said.

These soils are prone to dispersion, poor water infiltration, waterlogging, impaired root growth and low natural fertility.

In a recent study, only a third of monitored wheat crops achieved more than 80pc of their water limited yield potential, with waterlogging and poorly timed irrigation some of the key factors contributing to the yield gap.

The first of the investments, Optimising farm scale returns from irrigated grains: maximising dollar return per megalitre of water, will build on the GRDCs past irrigation investments to assist growers and advisers to make informed decisions to drive improved returns under irrigation.

The Development and validation of agronomic practices to realise the genetic potential of grain crops grown under a high yield potential, irrigated environment in the northern and southern regions investment will involve on-farm trials demonstrating agronomic practices which address priority constraints or opportunities for key crops in order to maximise system profitability.

The Increasing yield potential of irrigated crops in the northern and southern regions through novel amelioration techniques that improve soil structure investment will focus on addressing issues associated with soil constraints unique to irrigated cropping areas.