Dr John Kirkegaard1 

1Csiro Agriculture And Food, ,

Benchmarking farmer yield against a physiologically defensible yield potential has been an effective tool for crop yield improvement in Australia.  The approaches used to assess yield potential in water-limited environments have sensibly focussed on water-limited yield potential.  These vary from simple and accessible seasonal calculators such as that developed by French and Schultz (1984) up to sophisticated daily timestep models such as APSIM which underpins yield predictions in YieldProphet.  In the high rainfall zone, there will often be cases where water supply is not the major limit to yield, but rather the ratio of light and temperature (photothermal quotient – PTQ) in the critical period of yield formation.  Lower light and warmer temperatures in this period speeds development and reduces photosynthesis during the period when grain number is determined.  The relationship between PTQ and yield potential in wheat has been well described and has been demonstrated to be an accurate predictor of potential yield when no other factors are limiting (e.g. water, nutrients, pest, diseases, temperature extremes).  We used published physiological relationships between wheat and canola to propose a simple relationship between potential yield and PTQ in the critical period for canola and tested it against high yielding canola crops in Australia’s high rainfall zone including a record 7.2 t/ha commercial crop in southern NSW.  A simple ready reckoner was developed that used a cascade of PTQ, water supply and N supply to consider the yield potential of field-grown canola in the high rainfall zone.


Farming Systems Agronomist



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