Optimising Sorghum Agronomy

UOQ 18058-001RTX

Why this project?
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Over the last fifty years increases in grain yields have been the result of improvements from breeding, improvements in agronomy and the cropping system, and their interactions (Fischer et al., 2014). There is also no doubt that the same drivers will be responsible for future yield gains, that is, identifying optimum combinations of agronomic management and cultivars, that make best use of available resources i.e. soil water and fertility at sowing, and the seasonal conditions.

 

Over the last 30 years, sorghum yields in the Northern Grains Region have increased on average ~41 kg ha-1 year-1 (Potgieter et al., .2016). If only considering the last 16-years average yield gains were ~61 kg ha-1 year-1, equating to $20 ha-1 year-1. They also showed that yield gains were higher in dryer than wetter environments. This might reflect on the strategies of Australia’s sorghum breeding programs, the larger adoption of conservation agriculture practices in the more marginal environments, and the low levels of farmers’ investment (i.e. risk averse managements) that limit yields in the best environments and seasons (Roxburgh, 2017).

 

More recently, results from on-farm research by UQ00075 and DAN00195, identified yield differences of up to 60% between optimum and non-optimum combinations of sorghum hybrid and agronomy, across sites yielding between 1 and 8 t ha-1. A detail analysis of the Qld data set (Rodriguez et al., 2018; Clarke et al., 2018), confirmed that those optimum combinations of hybrid and agronomy, reduced water stresses around flowering (Hammer et al., 2014), and produced higher yields. These are examples of how identifying combinations of hybrids and agronomy can reduce the likelihood of water stress around flowering and increase yields. Understanding the principles of how to match hybrid, agronomy and environment provides a reliable tool for farmers and consultants to design more profitable and less risky sorghum production systems.

 

In the Northern Grains Region, managing heat and moisture stresses around critical growth stages remains the focus for sorghum adaptation and systems agronomy. For the case of heat and water stresses around flowering, the main adaptation strategy farmers have to reduce yield losses, is to avoid the overlap between stress events and flowering, by targeting optimum flowering windows and managing canopy size. Initial results from UQ00075 and DAN00195 show that to fit the flowering of sorghum around low risk windows for heat and water stresses, the crop would need to be sown into temperatures lower than the recommended 16°C, and with higher risks of frosts events. Under these conditions, achieving rapid and uniform crop establishments, and balancing likely benefits of reduced stresses around flowering, with the higher risk of frost damage, is essential.

 

Initial results from early sorghum trials between the Liverpool Plains in NSW and Warra in Qld, showed that:

  • Sowing at soil temperatures of 8°C at 0.1m of soil depth, significantly delayed and reduced crop establishment resulting in failed crops;

  • Sowing at temperatures of 12°C at 0.1m of soil depth, resulted in up to 75% of crop emergence within 11 days.

  • Early sowings of sorghum during early August at Warra QLD took around 100 days to reach flowering i.e. early and mid-November and reduced the likelihood of heat stresses to less than 10 in 100 years based on long term climate records.

  • For the 2017/18 season at Warra Qld, sowing into moisture during early August on a full soil profile, allowed the crop overcome an early dry spell (30+ days with no rain after sowing) and achieve yields of more than 7 t ha-1.

  • The crop was harvested during mid to late December, increasing the likelihood of refilling the soil profile and to double crop into a winter crop.

Even though these results are encouraging, significant questions remain to be tested before the practice could be promoted with industry, these relate to:

 

  1. Crop establishment: Present sowing recommendations indicate that sorghum “should be planted when the soil temperature at the intended seed depth is at least 16°C (preferably 18°C) for 3–4 consecutive days and the risk of frosts has passed”. However, our initial results, suggest that crops could be successfully established on colder soils (~12°C at planting depth) with good moisture and ground cover that reduces evaporative losses. Other factors likely to be important include seed quality, crop residue cover, soil moisture, soil type, and hybrid genetic differences.

  2. Early frost damage: Air temperature thresholds (intensity) and duration of damaging frosts in sorghum during early vegetative stages haven’t been clearly established. There is a need to better define the likelihood of early frost damage so that early sowing decisions can be better informed. Other factors likely to affect frost damage, that remain un-known, are crop residue cover, soil moisture, soil type and hybrid.

  3. Stresses around flowering, grain yields and risk of uneconomical crops: There is a need to produce information on how alternative hybrid and agronomy combinations, including early sowings, change the frequency of stress environments around flowering, and how these changes impact on likely yields and risks of uneconomic crops across the Northern Grains Region. This information needs to also be packaged and delivered in a way that can be used to inform farmers’ decisions. Remaining questions include:

  4. Cropping system benefits: Initial simulations with APSIM show potential increases in the likelihood of double cropping a winter crop after a longer summer fallow. For example, a crop planted in early August at Warra Qld, would take 100 days to reach flowering, and be harvested during mid or late December, leaving a longer fallow into the next winter crop. Though magnitude of the benefits and risks across the Northern Grains Region need to be properly quantified. Questions remain on how often this is likely to happen, what are the implication in subsequent crops, profits, and risks.

The overall aim of this project is to answer How do combinations of hybrid and crop managements positively modify stress environments and yield distributions in early sown sorghum; and how the practice positively influences the cropping system, increases farm profits and reduces risks?

 

This project will answer questions across the five themes above:

  1. Crop establishment

    1. How early is too early to sow sorghum across the highly diverse sorghum growing environments of the Northern Grains Region?

    2. How do we define early sowing in the key sorghum regions?

    3. What is the response of crop emergence (%) to soil temperature at and following planting?

    4. What factors modify this response e.g. ground cover, soil type, planting depth, hybrid, and seed size?

    5. How can land managers evaluate seed quality and use seed quality information to inform early planting decisions?

  2. Early frost damage

    1. How do frost thresholds change throughout crop development and how does genotypic selection and agronomic management e.g. residue level and row configuration, influence these thresholds?

    2. What is the % of likely crop damage in early sown crops across the Northern Grains Region?

    3. What tools are available to inform frost events across the Northern Grains Region?

  3. Stress around flowering, grain yields and risk of uneconomical crops

    1. Does early sowing reduce water and heat stress at flowering?

    2. How can the probability of heat stress during the critical times of flowering and grain filling be minimised?

    3. What are the impacts from non-standard sowing times for sorghum and what are the key variables controlling these?

  4. Cropping system benefits

    1. What overall farming system gains (if any) are available across crop sequences in terms of $/ha/mm (water) and cropping intensity?

 

References

  • Clarke et al., 2019 Understanding the diversity in yield potential and stability among commercial sorghum hybrids to inform crop designs. Field Crops Research 230, 84-97

  • Borrell AK, et al., 2014 Drought adaptation of stay-green sorghum is associated with canopy development, leaf anatomy, root growth, and water uptake. J Exp Bot  doi:10.1093/jxb/eru232

  • Fischer et al., 2014 Crop yields and global food security: will yield increase continue to feed the world? ACIAR Monograph ISBN: 978 1 925133 05 9 (print), 978 1 925133 06 6 (PDF)

  • Hammer et al., 2014 Crop design for specific adaptation in variable dryland production environments Crop and Pasture Sci 65, 614-626

  • Rodriguez et al., 2018 Predicting optimum crop designs using crop models and seasonal climate forecasts. Nature Sci Reports DOI:10.1038/s41598-018-20628-2

  • Roxburgh C 2017 PhD Thesis, The University of Queensland

For more information:
                              Prof Daniel Rodriguez  (UQ-QAAFI)     Darren Aisthorpe (DAF)      Loretta Serafin (NSW DPI)
                              Dr Joseph Eyre  (UQ-QAAFI)

© 2019 by QAAFI's Farming Systems Research Group