Agriculture Reference
In-Depth Information
and crop management, represents the highest level of system complexity; these can
incorporate a wide range of intra- and inter-specific mixtures and intercropping
together with temporal diversity.
However, in addition to the biological inputs necessary for the success of highly
diversified systems, there is a need to consider the market aspect. Developments
towards highly diversified systems are best served by appropriate local marketing
strategies. We also believe that development of systems in these directions will
probably be the best answer to both reducing the pressure towards global climate
change and to surviving the effects of such changes as they become more obvious.
10.8 CONCLUSIONS
Crop diversification can influence the agricultural ecosystem in many ways, from
abiotic effects on microclimate, erosion and soil structure, to biotic effects on
pathogens, insects, weeds and the crops themselves. We need to seek the positive
effects that emerge from the use of what we have termed functional diversity.
There has been a tendency to concentrate on specific aspects of the use of
diversification, for example, in the large body of work concerned with cultivar
mixtures and disease restriction. One advantage of this focused approach is that it
has facilitated the development of large-scale examples of simple changes (wheat
mixtures in the USA, barley mixtures in the GDR, rice mixtures in China) that can
be introduced easily with the existing technology (the Chinese harvest by hand…)
leading to reduced costs, increased production and less stress on the environment.
Progress towards increased exploitation of functional diversity in developing
countries is accelerating rapidly and on a large scale. For example, there is
considerable interest in rice-pasture rotation systems for the development of large
areas of South American savannahs. At the same time, care will be needed, of
course to ensure that the natural biodiversity of those areas is not lost.
Although it seems clear that more complex levels of diversification will lead to
increases in interactions among the components involved, relatively little work has
been attempted in these directions, despite their likely importance. Indeed, because
of the difficulties of analysis at high levels of complexity, it may be possible only to
follow and analyse the major end effects.
A major deficiency in the development of diversification strategies is that there
are often few cultivars of species available that have been actively selected for good
performance in diversification strategies and systems. This is highlighted by
examples of diversified systems that do not work (e.g. Daellenbach
et al
., 2005).
It also raises a more general question for mixtures generally of whether the
literature gives an adequate picture of reality: is there a tendency for positive results
to be published more than negative? We are also aware from our own experience
that negative results are sometimes obtained from inadequate trial designs. It has to
be accepted also that the positive returns from diversification strategies may
sometimes be inadequate. For example, rotations that are adequate for controlling
persistent weeds or pathogens may be too long in relation to other needs in a farm
plan.
