Agriculture Reference
In-Depth Information
TABLE 1.25
Definitions of Yield Measures
Yield (Symbol)
Definition
Estimation
Average farm yield (FY)
Average yield achieved by farmers in a
defined region over several seasons
Regional or national statistics, ground
or satellite surveys of fields
Economically attainable
yield given current markets
and institutions (AYa)
Optimum (profit maximizing) yield given
prices paid/received by farmers, taking
account of risk and existing institution
On-farm experiments or sometimes
crop models
Economically attainable
yield assuming efficient
markets/institutions (AYb)
Optimum yield given prices that would
prevail in efficient markets with
well-functioning risk insurance markets
On-farm experiments or sometimes
crop models
Potential yield (PY)
Maximum yield with latest varieties,
removing all constraints, including
moisture, at generally prevailing solar
radiation, temperature, and day length
Highly controlled on-station
experiments or crop models
calibrated with latest variables,
well-monitored crop contests
Water-limited potential yield
(PYw)
Maximum yield under normal rainfed
conditions, removing all constraints for
PY except for moisture
Highly controlled on station
experiments or crop models or crop
contests
Theoretical yield (TY)
Maximum theoretical yield for prevailing
solar radiation based on prevailing
knowledge of crop physiology and
photosynthetic efficiency
An accepted estimate is given by the
initial slope of the photosynthesis
versus solar radiation response curve
discounted for dark respiration
Source:
Adapted from Fischer, R. A., D. Byerlee, and G. O. Edmeades. 2009. Can technology deliver on the yield chal-
lenge to 2050? Paper produced for the FAO expert meeting on how to feed the world in 2050, Rome, 24-26 June,
2009. Food and Agricultural Organization of the United Nations Economic and Social Development Department.
Rome, Italy.
genotype in a given environment as determined, for example, by simulation models with plausible
physiological and agronomic assumptions. Fischer et al. (2009) presented several definitions of yield
measures (Table 1.25), including potential yield. The potential yield of several crops has grown sub-
stantially in the past several decades through breeding, along with improved management practices
and this has driven farm yield growth (Fischer et al., 2009).
Improved crop nutrition, especially N has made a huge increase in yields in developed as well
developing countries. For example, in wheat in the United Kingdom, the optimum dose of N fertil-
izer, now about 200 kg N ha
−1
, increases yield about twofold (Jaggard et al., 2010). Between 1950
and 1980, average N dressings for winter wheat increased from 50 to 180 kg ha
−1
but have risen only
slowly since then (Jaggard et al., 2010). Today, it is rare for crops in countries with well-developed
arable agriculture to receive suboptimal doses of N fertilizers, and applications are falling slightly
as farmers fine-tune their agronomy (Jaggard et al., 2010).
1.2.7.1 Components of Potential Yield
Crop physiologists have developed useful equations for calculating or exploring potential grain yield
and its components under radiation- or water-limited conditions (Monteith, 1977; Passioura, 1977).
These equations can be written or described as below:
PY
=
total aboveground dry weight (TDW)HI
×
(1.1)
∫
(1.2)
PY
=
PAR
×
UE
×
HI
i
