THE CLIMATE KELPIE BLOG: Assessing and managing heat stress in cereals
Investigate the meteorology and climatology of spring heat events on the southern grains wheat belt.
Develop a risk-management package for growers.
2009 – 2013
Most growers understand that the main management strategy to minimise heat events is to optimise the flowering window through sowing time and variety choice. The challenge is to characterise this risk in terms of likelihood and consequence.
- Characterising the meteorology of spring heat events in southern Australia: We examined the synoptic weather charts for a range of spring heat events such as October 2004 and November 2009 and found that the southern Australian grains belt is subject to two dominant influences, a cold maritime influence from the south and a warm to hot continental influence from the north. A heat event in spring coincides with a high pressure system to the east and an approaching cold front. This combination leads to a northerly flow of air (and associated hot conditions) followed by a south westerly (associated cool conditions). In spring the systems tend to move relatively quickly leading to heat spikes rather than the summer heat waves. It is not unusual to have the cold front followed by a high pressure system and a radiation frost.
- Characterising the climatology of spring heat events in southern Australia:The importance of heat events and access to climate files have led to a number of applications that can generate days over say 30 or 35 degrees in a given window. In addition to Yield Prophet, we have interacted with the developers of CropMate and Scott Chapman CSIRO who mapped the last frost day and first heat day (>35 degrees). A finding from this project was that when the hot days are placed in context of the flowering time of wheat that cooler high to medium rainfall regions are at a high or higher risk of hot days at the time of flowering than hot low rainfall sites.
- Understanding the impact of heat events: We ran field experiments using portable heating chambers over 4 seasons to look at the effect of a single hot day (around 35C +) on wheat, but with a slightly different focus in each season. In 2009, significant reductions in individual grain mass, grain number and yield were observed. In 2010 the focus was on the timing of the heat event; although we measured a 10% reduction in yields around early heading there were no significant results. In 2012, we looked at the interaction between temperature and water stress using Gladius grown in pots outside. While the water stressed pots showed more prominent leaf curl during heating, this did not result in significantly less yields than the well watered pots. Heated pots resulted in roughly 10% reduction in grain weight for the main stems compared to the controls (non-heated), but showed no difference in the number of grains.
- Risk management: The spreadsheet we developed enables user-defined damage functions as a family of curves from 25 degrees to 40 degrees. These curves relate phenological stage (x axis) to damage (y axis). In this project we have compared the damage functions used in Yield Prophet and Australian Grains Technology with a series of curves derived from our interpretation of the literature. Versions of the spreadsheet and risk management package have been used as part of meetings discussing climate risk with growers on upper Eyre Peninsula, Upper North Farming Systems group, Birchip Cropping Group and Mallee Sustainable Farming Systems. We have also presented information to medium to higher rainfall groups at Bordertown, Keith, Turretfield and Mannum.
Read the final report [PDF 6.5 Mb]
Dr Peter Hayman
South Australian R&D Institute
Phone: 08 8303 9729
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