Agriculture Reference
In-Depth Information
A detailed analysis of the past decade or so (Slafer et al., 1994) indicated that worldwide wheat
yields might be asymptotically approaching a ceiling, as average yields did not increase from 1990
to 1995. However, yield potential data of CIMMYT (Centro Internacional de Mejoramento de
Maize Y Trigo; Mexico) cultivars developed from the 1960s (Fageria et al., 2006) do not indicate a
plateau. Indeed, the average increase per year was 0.9% (Braun et al., 1997). This genetic progress
for increasing the yield potential was closely associated with an increase in photosynthetic activity
through the ideal plant canopy. Both photosynthetic activity and yield potential increased over the
30-year period by 25% (Fageria et al., 2006).
Similarly, an estimated 50% of the increase in U.S. wheat yields from 1954 to 1979 can be cred-
ited to genetic improvement (Schmidt, 1984). The introduction of semidwarf cultivars of wheat
had a large impact on the productivity of wheat in the Corn Belt and the Great Plains of the United
States, and is probably the major source of genetic gain in both regions (Feyerherm et al., 1988).
Semidwarf cultivars were planted on more than 90% of the area planted with wheat in the Corn
Belt by 1979, when the genetic gain in productivity was as high as 74% (Siegenthaler et al., 1986).
In the Great Plains states (Kansas, Nebraska, and Oklahoma), semidwarf cultivars occupied only
9%, 1%, and 38%, respectively, of the area planted with wheat, and genetic improvement for yield
was only 45%. However, the area planted with semidwarf cultivars by 1984 increased to 70%,
38%, and 76%, respectively, in the three states, and the genetic improvement increased to 61%
(Feyerherm, 1988).
Since the beginning of the 1960s, grain yield of winter wheat has increased by about 120 kg
ha
−1
year
−1
in France. This increase was mainly related to the genetic improvement of cultivars
and the use of adequate levels of N (Gouis and Pluchard, 1997). Average yields of wheat in the
United Kingdom rose from 3 to 8 Mg ha
−1
while the world average has risen from 1.08 to 2.7 Mg
ha
−1
(Jaggard et al., 2010). Reilly and Fuglie (1998) reported that the average yields of 11 crops
in the United States had increased by between 1% and 3% per year during the past half century
and the trend was linear or exponential, showing no sign that the rate was slowing down. A
large study by Hafner (2003) showed that the national average yields of wheat, rice, and corn in
188 countries were mostly increasing, that the increase had been predominantly linear, and that
the biggest producers' yields had increased at more than 33.1 kg ha
−1
year
−1
. In the developed
and developing countries, much of this increase has been due to the use of N fertilizers, the use
of adequate crop protection measures, and also planting high-yielding crop cultivars (Jaggard
et al., 2010).
Sharma et al. (2012) quantified the genetic yield gains in CIMMYT's (International Maize and
Wheat Improvement Center) spring bread wheat (
Triticum aestivum
L.) in the Elite Spring Wheat
Yield Trial (ESWYT) distributed over the past 15 years (1995-2009) as determined by the perfor-
mance of entries across 919 environments in 69 countries. Across locations in all countries, mean
yields of the five highest-yielding entries showed an annual gain of 27.8 kg ha
−1
(0.65%) compared
to Attila, a check cultivar. These authors concluded that there is no evidence for stagnation in the
genetic yield gain in the CIMMYT-developed elite lines for irrigated wheat environments world-
wide but the genetic yield gain maintains a linear yield potential increase.
1.2.4.2.1.3 Corn
The global food supply-demand model predicts that the global demand for
corn will increase from 526 million metric tons to 784 million metric tons from 1993 to 2020, with
most of the increased demand coming from developing countries (Duvick and Cassman, 1999).
Assuming no increase in maize production area, an annual growth rate in corn yield of about 1.5%
will be needed to meet this demand. However, from 1982 to 1994, the yield growth rate for corn
was about 1.2% worldwide and only 1.0% in developed countries as a group, which account for
the majority of total corn production. The situation has not been changed in corn yield increase in
the developing countries in the past decade. Hence, more efforts will be required in the future to
improve corn yield genetically as well as improved management practices to meet the world demand
for this cereal.
