Take home messages

• The critical developmental period for wheat and barley yield spans from late stem elongation to 1 week after flowering – management of water use and crop canopy needs to better consider this phase.
• Modern genetics and crop management (sowing time and amelioration) are achieving higher water use efficiency with transpiration efficiencies >25kg/ha/mm and evaporation <60mm.
• More analysis is needed on the role of tactical agronomy in shifting from conservative to higher input in seasons of favourable yield.

Background

A new GRDC project (CSP2404-020RTX - Profitable Yield Frontiers (PYF)) is focused on supporting tactical agronomy decisions in low to medium rainfall zones of the Southern region to achieve water-limited yield potentials. The project also connects to the Sandy Soils II project (CSP2403-017RTX), which aims to enhance water productivity on ameliorated sands. In these rainfall zones, early-season decisions often account for most of the crop expenditure. While higher inputs or adjusted timings can influence yield under different seasonal scenarios, knowing when and how to react, and the likely return, is challenging. Agronomic interventions must address the fundamentals of crop growth to deliver a yield response. Beyond sowing date, genetics, and nitrogen (N), opportunities to influence yield potential in season are limited.

Our goal is to develop a responsive agronomic system that increases yields without substantially raising risk or costs. We conducted a series of experiments across south-eastern Australia to:

• link tactical agronomy to physiological changes in the critical period and yield
• identify key benchmarks (crop and soil traits) for actionable decisions during the season
• lift water-limited yield potential in low to medium rainfall zones.

We are shifting towards a proactive approach to water use, focusing on setting up the crop canopy for success. Water-limited yield calculations are often done retrospectively, providing limited support for real-time adjustments. Seasonal agronomy outcomes vary by location and year, making predictions challenging and restricting our ability to effectively close yield gaps, maximise water-limited yield, and enhance profitability. In 2024 — a season defined by summer rainfall, a late break, and low in-season rainfall — our work focused on understanding crop canopy dynamics during the critical period and refining agronomic benchmarks. This will help to better position crops for success and adapt to seasonal water supply fluctuations.

The framework for grain yield is based on three key physiological principles:

• yield is primarily determined by the number of grains produced – more potential grains mean higher potential yield, making processes that determine grain number worth focusing on (Fischer et al. 2008)
• grain number is determined during a species-specific critical period
• environment and management affect three key traits during this period: duration, rate of growth, and biomass partitioning to grain (Slafer et al. 2023).

The most sensitive part of the critical period for wheat and barley occurs just prior to flowering, when grain number (and therefore, yield) is most sensitive to environmental factors like water, temperature, and nutrients. Water deficits during the critical period greatly influence grain number and yield. Aligning this phase with periods of minimal water stress and/or access to more water can enhance yield potential. Cossani and Sadras (2021) showed that reducing the duration of the critical period from 90 to 30 days can lead to a linear decline in yield from ^~6t/ha to <0.5t/ha in low to medium rainfall zones (L/MRZ), driven mainly by temperature. Porker et al. (2025) found that conditions during the critical period explained over 70% of yield variation in high rainfall zones (HRZ) due to sowing date, temperature and radiation, emphasising the importance of aligning agronomic practices with this critical phase.

Water-limited yield potential (WLYP) refers to the yield of an adapted crop grown under rainfed conditions, where best management practices minimise nutrient, pest, and disease limitations. Agronomic and genetic improvements have substantially closed the gap between achieved and water-limited yields (Fischer et al. 2014, Hochman et al. 2017). In southern and Western Australia, these improvements have increased transpiration efficiency (from 20 kg grain/mm transpired to 26kg grain/mm transpired) and reduced soil evaporation (from 110mm to 60mm, and as low as 45mm in Western Australia) (French and Schultz 1984, Sadras and Angus 2006, Sadras and Lawson 2013, Harries et al. 2022). Key mechanisms for improved water use efficiency (WUE) include greater transpiration efficiency and reduced non-productive water losses. The concepts of growth at the right time, managing evaporation, and crop transpiration and its link with vapour pressure deficit can help understand why different practices influence water use. While soil measurements for water and N availability are foundational for agronomic decisions, they fall short of providing a complete assessment for the management of WLYP due to their inability to account for dynamic factors like evaporative demand or crop growth rates. New diagnostic tools for measuring crop status in terms of water and N, such as simultaneous carbon isotope and N dilution curves, could contribute to better link plant indicators towards more responsive and risk-aware agronomy.

Materials and methods

Factorial small plot experiments were carried out in 2024 to create different canopy structures, utilising sowing date, genetics and N in the PYF project. Crop growth, water use, and yield has been extensively measured and a few examples of results are included here to explain the physiological processes. Supplementary water (30mm) was applied to treatments at the start of the critical period to determine the value of extra water and the response of different agronomy strategies. The latest genetics, including Shotgun Wheat, Neo Barley, and varieties of differing phenology and architecture, were included in these experiments. Sowing date and emergence targets were aimed at 25 April – 10 May, and a later emergence 3 weeks later (or with the break).

Similarly, as part of the Sandy Soils II project, small plot experiments were established in 2024 at three sites with five deep ripping treatments (nil, deep ripping, deep ripping with passive inclusion, deep ripping with active inclusion, and deep ripping with spading) and implemented in combination with different nutrition treatments. Plots were sown to Tomahawk CL Plus wheat on 29 May 2024 and emerged with the early June break in that example.

Results and discussion

Advancing the productivity frontier with new genetics and management, Lock, EP, 2024

Experiments at Lock in 2024 demonstrated that if earlier emergence could have been achieved in 2024, it was possible to grow more dry matter during the critical period, achieve higher grain number and higher yields (Figures 1 and 2). Even when delayed emergence treatments received an extra 30mm of additional water (supplementary irrigation) at the start of the critical period, they still only yielded equivalent to rainfed treatments that emerged in early May. While soil N was high, additional early N in this example did not influence growth nor show signs of haying off or negatively influence yield (Figure 2). This underscores the value of managing the timing of growth and its impact on yield potential.

Figure 1. The value of crop growth depends on timing and rate of growth. Evidence from sowing date, N, and supplementary irrigation treatments at Lock in 2024. The arrow shows emergence dates for each sow date (TOS), and the shaded boxes in the blue and red area is the critical period from 30d before to 10d after anthesis. Low N = 25kg N/ha, High N = 100kg N/ha, all applied prior to the onset of stem elongation. The additional 30mm of water was applied at the start of the critical period (flag leaf emergence) via dripper irrigation as indicated by the arrows.

Figure 2. a) Relationship between dry matter accumulated between flag leaf emergence and the end of flowering (growth in the critical period) for early emergence (●), and later emergence (♦) and grain number, and b) grain number and grain yield (t/ha). Closed circles represent extra 30mm of water applied at the start of the critical period at Lock in 2024 and open circles rainfed. The three data points within each treatment represents three levels of N. Different letters denote treatment differences at the 5% level.

These experiments provide valuable benchmarks and reinforce that productivity gains are achievable through combinations of modern genetics and improved management practices. They highlight the potential of strategies which ensure early emergence and align critical growth periods with environmental conditions, as demonstrated at Lock in 2024. The results from Lock (Table 1) illustrate the benefits of early sowing and timely management in maximising water use efficiency and yield under challenging conditions. Despite just 138mm of growing season rainfall, measured total water use reached 180–213mm due to substantial contributions from summer rainfall, and estimated in season evaporative losses of 40–80mm, with transpiration efficiencies approaching 26kg/ha/mm for grain yield. There is clear scope to further reduce evaporative losses and convert water more efficiently into yield by focusing on crop growth phases closely linked to yield potential (that is, critical period).

Table 1: Grain yield and water use comparisons of high nitrogen strategies at Lock 2024, in Neo Barley and Shotgun Wheat. The wheat treatments also received an extra 30mm of water applied as irrigation at the onset of the critical period for Lock*. Treatments sharing the same letter are not significantly different from each other, while treatments with different letters indicate a statistically significant difference in their effects at the 5% level. Water use numbers were calculated by subtraction and not yet analysed.

*received 15mm water at sowing to ensure established (added to in-season rainfall)

Soil amelioration improves water productivity, Wharminda, EP, 2024

Experiments at Wharminda (Eyre Peninsula), as part of the Sandy Soils II project, showed crop amelioration (0.5m deep ripping and mixing) addressing soil strength and spading addressing water repellence increased yields by almost 2t/ha (Table 2). Total crop water use (evapotranspiration) was calculated by soil measurements of water at sowing – soil water at harvest + in-crop rainfall (only 76mm). Water use in the critical period was calculated between flag leaf emergence and the end of flowering (only 11mm rainfall fell in this period).There were relatively small differences in total water use, in the deep rip and spade treatment, however 20mm more used compared to untreated. This extra 20mm was almost all available in the critical period, and almost 50% of the seasonal water use being used in the critical period in the deep ripping and spading strategy (Table 2). This is the period of peak sensitivity to stress and grain number determination, where small differences in water availability and use can equal large differences in yield and helps explain the large yield responses.. The final evaporation and transpiration components are yet to be analysed but previous results suggest a greater proportion of water is lost to evaporation rather than transpired from biomass on untreated sand.

Table 2: Grain yield and water use in response to soil management treatments at Wharminda, 2024. Treatments sharing the same letter are not significantly different from each other, while treatments with different letters indicate a statistically significant difference in their effects at the 5% level.

Conclusion

Results from 2024, a very dry season, emphasise the transformative potential of new genetics, early emergence and soil amelioration. It is possible to continue to increase grain yield through maximising resource efficiency by focusing on the critical period's sensitivity to environmental and management factors. We plan to develop new benchmarks that can assist in maintaining profitability in challenging low to medium rainfall zones.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC. The authors would like to thank them for their continued support. We thank the technical teams who deliver the experimentation for our projects. GRDC Project CSP2404-020RTX is a collaboration between CSIRO, AgCommunicators, AIREP, EPAG Research, SARDI, University of Adelaide, FAR Australia, Frontier Farming Systems, Hart Field site group, Elders, Birchip Cropping Group and AgInsights. GRDC project CSP2403-017RTX is a collaboration between CSIRO, the University of South Australia, Frontier Farming Systems, EPAG Research, Trengove Consulting, Soil Function Consulting, South Australian Research and Development Institute and University of Sydney.

References

Cossani CM, Sadras VO (2021). Nitrogen and water supply modulate the effect of elevated temperature on wheat yield. European Journal of Agronomy 124, 126227.

Fischer, R.A., Byerlee, D., Edmeades, G., 2014. Crop yields and global food security: will yield increase continue to feed the world?, ACIAR monograph series. ACIAR, Canberra.

French, R.J., Schultz, J.E., 1984. Water use efficiency of wheat in a Mediterranean-type environment. I. The relation between yield, water use and climate. Aust. J. Agric. Res. 35, 743–764. https://doi.org/10.1071/ar9840743

Harries M, Flower KC, Renton M, Anderson GC (2022) Water use efficiency in Western Australian cropping systems. Crop and Pasture Science 73(10), 1097–1117.

Hochman, Z., Gobbett, D.L., Horan, H., 2017. Climate trends account for stalled wheat yields in Australia since 1990. Global Change Biology 23, 2071–2081. https://doi.org/10.1111/gcb.13604

Porker, K., Poole, N., Warren, D., Lilley, J., Harris, F., Kirkegaard, J., 2025. Influence of photothermal quotient in the critical period on yield potential of cereals–A comparison of wheat and barley. Field Crops Research 321, 109658. https://doi.org/10.1016/j.fcr.2024.109658

Sadras, V.O., Angus, J.F., 2006. Benchmarking water-use efficiency of rainfed wheat in dry environments. Aust. J. Agric. Res. 57, 847–856. https://doi.org/10.1071/AR05359

Sadras, V.O., Lawson, C., 2011. Genetic gain in yield and associated changes in phenotype, trait plasticity and competitive ability of South Australian wheat varieties released between 1958 and 2007. Crop Pasture Sci. 62, 533–549. https://doi.org/10.1071/CP11060

Slafer GA, Savin R, Sadras VO (2023) Wheat yield is not causally related to the duration of the growing season. European Journal of Agronomy148, 126885.

Contact details

Kenton Porker
CSIRO Agriculture and Food
Waite Campus
Urrbrae SA 5064
kenton.proker@csiro.com
@kentonp_ag