Innovative research in South Australia has indicated that wheat growers may be able to employ some simple techniques to control the flowering time and yield of their crops.

Research into these new agronomy levers has been one focus of the strategic partnership between GRDC and the South Australian Research and Development Institute (SARDI).

Lead researcher Dr Kenton Porker says the one-year feasibility study explored alternative options that growers could use to manage their crop’s development – especially flowering time – in order to maximise yields.

Flowering time is critical for crop yield and the optimum flowering period for any location typically spans a relatively narrow period.

“We know flowering date is very important when it comes to maximising yield and minimising the trade-offs associated with frost, drought and heat stresses. So far, the best way to manage that has been through cultivar choice and sowing time,” Dr Porker says.

“However, those decisions all have to be made at the time of sowing, with the ability to establish the right cultivar at the right time depending on seedbed moisture and, usually, the timing of opening rains as a germination event.

“We set out to explore options that offer growers more flexibility to manage these seasonal variations with management tools in addition to sowing date and cultivar genetics.”

Flowering time

The study looked at a range of novel options to accelerate development in crops that emerged too late and delay flowering in wheat that was developing too quickly.

The research showed hormone application could shift flowering by two to three days in either direction. However, the responses were variable and the required frequency of application was unlikely to offer any practical solutions without further investigation.

Many of the potential options, such as hormone inhibition, also caused reduced growth and biomass accumulation, which had negative trade-offs in terms of crop yield.

On the other hand, defoliation of the plants to remove the main apical meristem at non-traditional timings was shown to delay flowering by up to 15 days and significantly increased yield compared to other early sown controls. This suggests there is an opportunity to maximise yields by adjusting flowering time into the optimum window.

“The results indicate that this approach may actually be very effective at altering the time of flowering and closing yield gaps across varying seasonal constraints and nitrogen levels,” Dr Porker says.

“It has the potential to offer growers a robust new avenue for maximising yield across seasons, regardless of the cultivar.”

A recent GRDC investment studying the management of early sown wheat, led by Dr James Hunt from La Trobe University, demonstrated that when new commercially available winter cultivars are established in early to mid-April, they can deliver yields similar to fast-developing spring varieties sown in the first week of May.

For most growing areas in South Australia, the timing of autumn rains provides an opportunity to establish crops before 25 April in approximately 30 to 55 per cent of years, depending on location.

Delayed emergence

However, a recent spell of dry autumns has also meant emergence could be delayed until late May or early June in a significant percentage of other years.

This means growers need to make sure the germination date of their crop matches the development speed of the variety sown in order for it to flower at the optimal time, Dr Porker says.

“Slower-developing winter wheats must be planted into a moist seedbed or ahead of a reliable rain forecast before 25 April, while fast-developing spring wheats should not germinate before 1 May in most districts,” he says.

In the absence of seedbed moisture, the alternative is to begin sowing into a dry seedbed and hope rain and germination will be delayed until the start of May.

Dr Porker says there are risks associated with either strategy. “One of the problems with dry sowing a fast-developing wheat early, for example, is that an unpredicted early rain event can cause the crop to germinate and flower too early, exposing the crop to yield losses from frost and poor biomass accumulation,” he says.

“Conversely, if germination of a winter wheat is delayed due to late rain, there will probably be a yield penalty because critical development periods are aligned with suboptimal conditions.

“Flowering is delayed and grain fill is subject to the increasing heat and moisture stress of summer.

“At this stage of the research, the potential to slow down cultivar development looks far more achievable than speeding up development.”

GRDC-SAGIT-SARDI grains trainee Brendan Kupke conducting his plant hormone trials with greenhouse grown wheat.

As part of the project, Dr Porker mentored University of Adelaide student Brendan Kupke under the GRDC-South Australian Grain Industry Trust Fund (SAGIT)-SARDI grains traineeship program.

“Brendan conducted a large screening project to determine the effect of various commercially available plant growth regulators and hormones on flowering dates for wheat, canola and barley,” Dr Porker says.

“He identified a number of key hormones with good potential through that research and is now doing more detailed growth regulation studies to determine application rates and timings.”

Dr Porker says the success of the novel techniques identified in this project is a potential paradigm shift that will reduce the yield gap associated with missing earlier planting opportunities due to seasonal constraints.

“These approaches could be particularly valuable to growers in the low-rainfall zone, where opportunities for early sowing are less frequent and, as a result, keeping seed for winter cultivars is less attractive,” he says.

He hopes additional research will help refine the timing and frequency of such interventions, in order to provide a clear set of guidelines for growers.

“The objective is to deliver a suite of crop management strategies that are independent of cultivar choice, sowing date and autumn rain events,” he says.

“It’s about reducing risk and stabilising whole-farm yields.”

The outcomes of this project were delivered via the strategic research partnership between GRDC and SARDI. The GRDC-SARDI partnership has facilitated a range of projects that provide innovative research outcomes relevant to SA’s cropping zones.

The project included experiments at Loxton, Minnipa, Tarlee and Cummins, and involved research partnerships with La Trobe University, EPAG Research, Eyre Peninsula Agricultural Research Foundation and the Mid North High Rainfall Group.

More information: Dr Kenton Porker, 0403 617 501, kenton.porker@sa.gov.au