Agriculture Reference
In-Depth Information
The biological relationship between f floral diversity and both pest and beneficial insects has
been studied extensively. The importance of f lowers to attract beneficial insects for adult
feeding as well as grass banks as overwintering sites for predatory beetles is now fully recog-
nised (Van Emden 2003). Uncultivated land, hedgerows inside crops, in allied crops and in
neighbouring areas can serve as refugia for beneficial insects such as parasitoids of aphids
(Verkerk
et
al
. 1998). The data generated by Langer (2001) was based on an organically farmed
experimental system, and indicated that short rotation coppice hedges and clover/grass leys in
the rotation may increase diversity and activity of parasitoids attacking cereal aphids. Besides
the positive effects of biological pest control, from a farmer's point of view, negative interac-
tions such as pests overwintering in hedges and weeds invading from field margins are also
important. Many farmers considering converting to organic farming fear that such problems
will be very difficult to manage. Although some mechanisms of natural enemy enhancement,
such as increasing diversity within cropping systems, have been explained in specific systems,
it is difficult to show universal trends due to the great diversity of systems and competing
processes that vary under different conditions (Verkerk
et
al
. 1998, Tybirk
et
al
. 2004).
Concerning domesticated species, organic farming aims for a greater diversity of crops in
their rotation. Wide crop rotations are essential as a means of disease and pest prevention.
They also contribute to maintaining soil fertility, particularly if N-fixing legumes are part of
the rotation. While organic farming standards recommend cultivating site-adapted crop vari-
eties, organic farmers (just like their conventional colleagues) often choose modern high-
yielding varieties. Nevertheless, the preservation of old land varieties and breeds is an important
initiative within the organic farming movement (Stolze
et
al
. 2000).
Faunal diersity
The effects of organic farming on faunal biodiversity have been studied, particularly for soil
fauna and birds. In most cases, organic farming displays a greater faunal biodiversity than
conventional farming. Key factors are: greater fauna-friendly crop protection management,
the organic fertilisation regimes, the more diversified crop rotation, and the more structured
landscapes with semi-natural habitats and field margins (Stolze
et
al
. 2000, Alföldi
et
al
. 2002).
Landscape structures are essential for the survival of many invertebrates, especially due to
favourable food and overwintering conditions. They also function as habitat crosslinks
between meadows, fallows and field margins.
An analysis of some specific groups of fauna illustrates the interrelationships.
Earthworms
Earthworm populations can indicate the structural, microclimatic, nutritive and toxic situa-
tions in soils. They are highly suitable bioindicators of soil fertility, and they are known for
their sensitivity to synthetic pesticides and to many agricultural practices (Mäder
et
al
. 1996,
Pfiffner and Mäder 1997). Earthworms help to improve soil structure and provide a high con-
centration of nutrients in a form accessible to plants (Alföldi
et
al
. 2002). Many investigations
in Europe and North America show that organically managed soils tend to exhibit a greater
abundance and species number of worms compared to conventionally managed plots or farms
(review in Pfiffner 1997).
Arthropods
Pesticides can affect beneficial arthropods either directly via contamination, or through alter-
ation of the microhabitat and a reduction of their prey. In contrast to conventional farming,
synthetic pesticides are banned in organic farming and the use of a few approved natural pesti-
cides is very restricted. Most natural pesticides are not very selective and can therefore also
