Agriculture Reference
In-Depth Information
with 5 or 6 components outyielded the mean of the components, when grown separately, by
up to 15%. Yield increases were not simply a result of lower disease levels, since similar
results were obtained when plots were given a full fungicide treatment. Armour et al. [5]
suggested that high yields occur when the grain filling period coincides with the time of peak
solar radiation, as photosynthesis will contribute around 75% of grain yield [27]. Potential
yield will be lost by premature senescence of the canopy through drought, pest or disease
[62], so high-input systems utilise fungicides [22] and, if necessary, irrigation [45] to retain
green-leaf area.
4.1
56
53
Thousand
Grain
Weight
4.0
50
Me a n Gra i n
Width
3.9
47
3.8
44
Monoculture Mixture
Figure 5. Grain dimensions of 3 barley varieties grown in monoculture or as components in a 3-way
mixture.
Delaying canopy senescence is important in monoculture, as all the genotypes utilise the
same resources simultaneously [51], whereas within mixtures, a degree of temporal and
spatial variation may create an increase in resource availability. Essah and Stoskopf [16]
noted a yield advantage in barley mixtures where components contrasted in phenotype,
particularly where maturity differences enabled resources to be exploited over a slightly
longer period, while Sarandon and Sarandon [51] demonstrated an increase in total biomass,
in a wheat mixture, compared to that of the components. Both of these studies were carried
out on two-component mixtures and the potential to modify the canopy, exploiting spatial
variation, should be enhanced by greater complexity. Disease control will also be improved
and while spraying may not be eliminated, the need for prophylactic treatment should be
reduced [65]. In deriving a scheme for optimal bioethanol production from wheat, Swanston
and Newton [65] suggested the use of mixtures with at least five components.
There is, however, a requirement for a better understanding of the range of interactions
between mixture components. Sarandon and Sarandon [51] describe two possible interactions,
i.e. the competition for the same resources by plants that are phenotypically very similar and
the complementary utilisation of wider resources by plants with a degree of dissimilarity in
physical appearance or maturity. However, growers have noted a reduction in the expected
height differential between 6-row and 2-row barleys, when they were grown as mixtures [63]
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