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Episode 2: MSF Farm Talk | Overcoming reliance on the seasonal break – Early wheat establishment findings at Lameroo, SA

August 18, 2020 - 3:07 pm

Bonnie Flohr from CSIRO joined us in this episode to chat about her work on a case study based in Lameroo on soil, water and temperature thresholds for early wheat establishment.

The aim of this project is to determine the soil water requirements, and soil temperature limitations to the successful establishment of deeply sown long coleoptile wheat cultivars at the earlier sowing dates in the South Australian mallee environment. 

This SAGIT funded project is achieving this in three phases:

Model simulation to determine anticipated soil temperature and water scenarios in the mallee environment.
A controlled environment experiment with intact soil cores collected from the target environment, testing the impact of temperature and soil moisture regimes on plant establishment.
A 3-month field experiment that evaluates the effect of soil moisture and ground cover on soil temperature at early sowing windows.

Tegan: Welcome to the MSF Farm Talk Podcast.

I’m Tegan Buckley and today Bonnie Flohr from CSIRO is joining us in this episode to chat about her work on a case study based in Lameroo on soil, water and temperature thresholds for early wheat establishment.

Bonnie Flohr is originally from Lameroo in the Mallee. Bonnie completed her PhD in 2018 in wheat physiology at ANU in Canberra. In her new role, as a Postdoctoral fellow in Farming Systems at the CSIRO based in Adelaide, Bonnie’s work is focused on evaluating innovative cereal-legume pasture options and increasing understanding of soil-plant interactions that underpin productive, profitable and sustainable farm businesses.

Welcome Bonnie! Thanks for joining us!

Bonnie: Thank you very much for having me Tegan!

Tegan: So Bonnie you’re here on the podcast today to chat with us about your findings on your recent case study out of Lameroo. Can you give us a quick summary and run down of the study?

Bonnie: So as we know, the seasonal break is a highly anticipated rainfall event that starts sowing programs and promotes crop establishment on farms. However autumn rainfall is declining in south-eastern Australia, farm size is getting bigger and increasing heat and drought stress in spring make it increasingly difficult to get the whole cropping area sown at the optimal time.

We know the benefits of getting the crop sown on time, which includes frost, heat and drought avoidance at flowering time, and therefore higher yield. There are also benefits associated with early sowing longer season varieties, which include a longer growing season to accumulate resources and a longer duration to grow deep roots to access stored deep soil moisture. However, to see the benefits of early and timely sowing, we still rely upon a variable seasonal break to get crops established on time. To overcome reliance on the seasonal break, we need some novel genetic x management strategies. The South Australian Grains Industry Trust (SAGIT) funded this project to look at a potential adaptive strategy as a case-study in the mallee environment.

Tegan: What were some of the adaptive strategies you found to remove reliance on the seasonal break for successful crop establishment?

Bonnie: One potential strategy to overcome reliance on the seasonal break, is to sow cultivars with long coleoptile deeply into soil moisture that is accumulated during fallow periods and through crop rotation, which germinates with seed without needing a rainfall event. Our current varieties generally emerge best from a maximum sowing depth of 5 cm due to dwarfing genes associated with short coleoptiles, but it has been shown by colleagues at CSIRO in Canberra that we can use alternate dwarfing genes that also have the long coleoptile genes and can emerge from greater sowing depths safely.

In our study we use field and growth chamber experiments to evaluate the strategy in the mallee environment, using seed with long and short coleoptile.

Tegan: Were there any risks or concerns you had with the case study when it came to warmer soil temperatures commonly seen in early sown wheat?

Bonnie: A concern for the deep sowing/ long coleoptile strategy is that the warmer soil temperatures commonly associated with early sowing have the potential to shorten wheat coleoptiles therefore negating the long-coleoptile benefit, but is an effect that could potentially be offset by using stubble retention and deeper sowing into cooler soil.

So the aim of this case-study was to evaluate the potential for deep-sown wheat cultivars with long-coleoptiles to reduce the dependence on the seasonal break for successful crop establishment in the Mallee environment. To do this, we did some modelling, an experiment in a controlled environment experiment with plants grown under different temperatures, sowing depths, and moisture content with intact soil cores, and a field experiment that evaluated the effect of soil moisture and ground cover on soil temperature at early sowing windows.

Firstly, though the modelling we found that the median seasonal break in Lameroo is 11 May, but there is a 25% chance of a break occurring between 19 April and 11 May. Therefore, there is some chance for opportunistic early sowing here- even without the need for long coleoptile cultivars. But it also tells us having a cultivar that could be sown early, deeply into stored soil moisture would be very useful to increase establishment opportunities.

When looking at historical weather data, we also found that the seasonal break in the SA/Vic mallee has been delayed by 3-9 days in recent decades. Making timely crop establishment even more challenging.

In the soil temperature sensor experiment where we were comparing soil temperature under different two sowing depths (deep and shallow), stubble load, moistures at early and traditional sowing windows we found;

· The soil temperature in the field experiment was 6-8°C warmer in earlier sowing windows (March-April)

· Soil temperature was less variable and cooler at depth in early sowing windows compared to shallower soils.

· Stubble cover kept soils cooler during early sowing windows

· Deeper soils with stubble were cooler than shallow soils with stubble

In the controlled environment study, we measured coleoptile length and plant emergence of wheat with either long or short coleoptile, sown deeply or shallow under two temperatures that we recorded from the field temperature sensor experiment.

Here we found that soil temperatures experienced in the early sowing windows were unlikely to reduce coleoptile length in the mallee environment, but soil type and soil water moisture will play a more important role on emergence.

Bonnie: Thanks for joining us Bonnie, to conclude the episode, can you leave us with your key takeaways?

Bonnie: Our study in a controlled environment facility was set at the average soil temperatures measured in the field during early sowing windows (17°C and 23°C) and these temperatures did not affect coleoptile length in that temperature range. Therefore, our case-study suggested that soil temperatures experienced in the early sowing windows were unlikely to reduce coleoptile length, but soil type and water availability will play an important role on emergence.

The next step of this research is to take it to the field and use farm equipment to test the deep sowing strategy under field conditions. Some important considerations for future experiments include;

Soil type and re-compaction after deep sowing play an important role on emergence

We require fine-tuning of moisture requirements for successful crop establishment.

Requires further investigation under field conditions representing different field environments, soil types and farm equipment, especially sowing points.

Tegan: Great thanks so much for sharing with us! What’s next for you now?

Bonnie: I’m about to go on maternity leave with my first baby, but on my return, I hope to keep working in the genetic by management research space for cropping and livestock systems in our region with CSIRO.

Tegan: How exciting! All the best. Thanks Bonnie