Crop Yield Forecasting

drying have been taken into account (Keita, 2003) 1 .
An alternative classification relies upon the concept of yield gap Y g , which is closely linked to
the definition and measurement of the yield potential Y p . Agronomists generally refer to three
different levels of yield when modelling Y g :
• Yield potential Y p : the theoretical maximum yield that can be achieved in a given
agro-ecological zone with a given cultivar. It assumes an ample supply of water,
nutrients, or other yield-building factors and the complete absence of yield-reducing
factors such as pests and diseases (Van et al., 2013).
• Exploitable (or attainable) yield Y e : this takes into account growth-limiting factors
such as nutrient deficiencies and water stress (Fermont and Benson, 2011).
• Actual yield (or farmer yield) Y a : this takes into account growth-reducing factors
such as radiation, temperature, water, nutrients, management practices, weeds,
pests, diseases, and pollutants. It represents the yield that farmers obtain under
normal management (Rabbinge, 1993).
Thus, the yield gap is the difference between potential and actual yield (see Figure A1.2).
FIGURE A1.1
Classification of yield considering harvest and post-harvest losses
Grain yield per hectare
Biological
Yield
Harvest losses
(e. g. seeds
for the next
season)
Harvested
Yield
postharvest
losses (e. g.
losses during
cleaning,
threshing,
winnowing
and dryng
Economic
Yield
1
Storage losses are normally not included in the definition of economic yield, even though they may be important to
farmers (Fermont and Benson, 2011).
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Crop Yield Forecasting: Methodological and Institutional Aspects