Frost and heat stress are major issues for the Australian broadacre grain industry. Frost stress costs around $360 million in direct and indirect yield losses to growers each year, according to GRDC estimates, and I would hazard a guess that heat stress is at least as significant as frost. As a result, I’m pleased to announce that Yield Prophet users can now run input scenarios for their wheat and canola paddocks that are based on frost and heat-affected yield potentials. This should allow for improved decision making based on more realistic, comprehensive crop scenarios.

Until recently, the APSIM-Wheat and Canola models that drive Yield Prophet have not simulated the effects of heat or frost stress events on grain production.   Given the potential impact of these issues, it is possible that users have been basing input decisions on overly optimistic yield potentials when they are not accounted for. Fortunately, Lindsay et al (2015) and Lilley et al (2015) have developed functions that simulate the yield effects on wheat and canola respectively of frost and heat.  In the last week the Yield Prophet team has added these functions to Yield Prophet. 

The significant effect of frost and heat on the potential yield is illustrated by comparing the curves shown in Figures 2 and 3. For example, at the 50% probability there is a 15% and 7% reduction in yield for the nitrogen and water limited curves. Figure 3 overlays Figures 1 and 2 to show the differences between the yield potentials more clearly. You will be able to select which curves you see when you generate a report by ticking the check boxes.  

Figure 1: Water and nitrogen limited yield potential for a Kord wheat crop sown at Birchip in North Western Victoria on the 28^th of April 2016 (Generated 10 June 2016)

Figure 2: Water and nitrogen limited frost and heat adjusted yield potential for a Kord wheat crop sown at Birchip in North Western Victoria on the 28^th of April 2016 (Generated 10 June 2016)

Figure 3: Water and nitrogen limited yield potential and water and nitrogen limited frost and heat adjusted yield potential for a Kord wheat crop sown at Birchip in North Western Victoria on the 28^th of April 2016 (Generated 10 June 2016)

The effect of mild, moderate or severe heat and frost is expressed in Table 1, showing the percentage of years the event has been observed.  These reported frost and heat events are the cause of the reduced yields observed in the frost heat adjusted yield potential.

Table 1. Probability of Mild, Moderate and Severe frost and heat shock for a Kord wheat crop sown at Birchip in North Western Victoria on the 28^th of April (Generated 10 June 2016)

The functions that affect the yield in response to frost and heat are summarized in Tables 2 and 3 for wheat and canola respectively. 

Table 2. Minimum and maximum temperature criteria for frost and heat stress during sensitive growth stages (Zadoks growth stage) and estimated yield reductions caused

Table 3. Minimum and maximum temperature criteria for frost and heat stress during phenologically sensitive stages and estimated resulting yield reductions

References

Julianne M. Lilley A,C, Lindsay W. Bell B, and John A. Kirkegaard A (2015) Optimising grain yield and grazing potential of crops across Australia’s high-rainfall zone: a simulation analysis. 2. Canola Crop & Pasture Science, 2015, 66, 349–364

Lindsay W. Bell A,C, Julianne M. Lilley B, James R. HuntB, and John A. Kirkegaard B (2015) Optimising grain yield and grazing potential of crops across Australia’s high-rainfall zone: a simulation analysis. 1. Wheat Crop & Pasture Science, 2015, 66, 332–348

Kirkegaard JA, Lilley JM, Brill RD, Sprague SJ, Fettell NA, Pengilley GC (2015) Re-evaluating sowing time of spring canola (B. napus L) in south-1 eastern Australia – how early is too early?, Crop & Pasture Science