Agriculture Reference
In-Depth Information
soil fertility and the application of herbicides, insecti-
cides and fungicides, these would have to be used in
the comparison trial. However, older cultivars were not
grown under these conditions. Certainly, older cereal
varieties tend to be taller than newer ones and are
therefore more prone to lodging (flattening by wind
or rain) when grown under conditions of high soil fer-
tility. These considerations also show that cultivars are
bred to best utilize the conditions under which they are
to be cultivated. Nevertheless, several attempts to com-
pare old and new cultivars have been undertaken in an
attempt to determine the contribution of modern plant
breeding to recent yield increases.
In one comparison carried out in the United
Kingdom, winter wheats ranging in introduction date
from 1908 to 1980 were simultaneously evaluated in
field trials. In a similar experiment, spring barley culti-
vars ranging in introduction dates from 1880 to 1980
were compared. From the wheat cultivars available in
the mid-1940s the grain yield from this study was about
5.7 t ha
−
1
but from the most recently introduced cul-
tivars from 1980, yields were about 50% higher. There
was a similar improvement in barley yield over the same
period of about 30%. Therefore, considering these stud-
ies, breeding contributed about half to the more than
doubled cereal yield between 1946 and 1980.
In contrast, a study carried out in potatoes, with cul-
tivars with dates of introduction from 1900 to 1982,
(Figure 1.5) found that modern plant breeding had been
responsible for a very small contribution to the more
than doubled potato yield in the United Kingdom. This
study in potato may, in part, explain why 'Russet Bur-
bank', introduced before 1900, still dominates potato
production in the USA; while the cultivar 'Bintji',
introduced in 1910, remains a leading potato cultivar
in the Netherlands.
In conclusion, modern day crops have shown sig-
nificant yield increases over the past century. It would
be wrong to suggest that the major contributor to this
increase has simply been a direct result of plant breed-
ing. Increases have rather resulted from a combination
of plant breeding and improvements in crop husbandry.
For example, the increased use of inorganic nitrogen
fertilizer has greatly increased wheat (and other cereal)
yield. However, this was allied with the introduction of
semi-dwarf and dwarf wheat cultivars that allowed high
nitrogen fertilizer application without detrimental crop
lodging. Without the addition of nitrogen fertilizers
would the dwarf wheat cultivars have been beneficial?
Perhaps not. However, would high nitrogen fertilizer
application have been possible without the introduc-
tion of dwarf wheat cultivars? It is difficult to know.
The overall increase achieved to date has resulted in
both genetic and non-genetic changes in agriculture.
In the future the same is likely to be true: that the
next leap in crop productivity will result from a marked
change in agronomic practice, plus the introduction of
plant types that can best utilize this husbandry change.
What changes will these be? It is impossible to know
with any certainty. Recent moves to reduced tillage
systems may be one option that could be considered
and that would require specific cultivars to maximize
performance under these situations.
Similarly, advances in recombinant DNA techniques
may result in the development of crops with markedly
different performances and adaptations to those avail-
able today. Introduction of these crop types may neces-
sitate a major (or minor) change in crop husbandry
to utilize the potential of these genetically modified
crops.
20
15
THINK QUESTIONS
10
(1) 'The yield of many crops species has risen dra-
matically over the last 50 years. This has been the
direct result of plant breeding during this period
and hence the trend is likely to continue over the
next 50 years'. Briefly discuss this statement.
(2) Different
5
0
1900
1910
1920
1930
1940
1950
1960
1970
1980
Year of introduction
Figure 1.5
Saleable yield of tubers from potato cultivars
grown over a three year period. Yield is related to the year
that each cultivar was introduced into agriculture.
crop
species
originated
in
different
regions
of
the
world.
List
the
centre
of
ori-
gin of the following ten crop species:
Onion
