Community composition of soil organisms under different wheat-farming systems - Microbial Ecology in Sustainable Agroecosystems - page 89

fertility through the application of animal feces (Heckman 2006). Today, organic farming
refers to management strategies that avoid the use of inorganic fertilizers, pesticides, and
growth regulators to minimize environmental impact. These management strategies have
therefore been promoted as ecosystem-oriented agricultural production systems and may
contribute to a sustainable agriculture in the future (Häni et al. 1998). A long-term study
by Mäder et al. (2002) in Switzerland suggested that the profit under organic farming is
comparable to conventional farming for a number of row crops, while associated environ-
mental impact and soil degradation are reduced. Yields were on average 20% higher in
conventionally managed crops, but costs for pesticides and inorganic fertilizers adjusted
farmers' profits to the same level. The extrapolation of results of such small-scale studies
and related reviews to the potential of organic farming for sustaining a global food supply
(Badgley et al. 2007; Badgley and Perfecto 2007) has been challenged (Avery 2007; Cassman
2007). However, consumer awareness is increasing in several countries, and there is a
growing demand for environmentally sound agricultural products (Tilman et al. 2002;
Willer and Kilcher 2010). One of the mechanisms that have been put forward to explain
the relatively high yield in organic farms without making use of pesticides and inorganic
fertilizers is that organic crops are associated with more complex soil food webs (Haubert
et al. 2009; Crowder et al. 2010). These food webs can ensure sufficient nutrient availability
through decomposition of organic matter by soil organisms and may maintain pest densi-
ties at low levels (Zehnder et al. 2007; Birkhofer, Bezemer, et al. 2008).
In this chapter, we describe, for a long-term agricultural experiment, the effects of
different wheat-farming systems on the community composition of selected soil organ-
isms. We further provide information about the taxonomic resolution that is operational to
study the impact of management decisions (taxonomic sufficiency) and relate responses of
different soil organism groups to each other, to soil properties, and to ecosystem functions.
5.1.2 Taxonomic sufficiency
Recent approaches in biodiversity assessment are based on the definition of functional
groups or the use of higher taxonomic orders to serve the challenge of making biodiversity
research functional (Letourneau and Bothwell 2008) and economically feasible (Mandelik
et al. 2007). Detailed taxonomic information (e.g., species level) is often excluded from these
studies, and functional groups or traits are defined at higher taxonomic levels (e.g., Ferris
et al. 2004; Franklin et al. 2005). These approaches are motivated by the fact that species
identification is laborious and that the scientific community suffers from an ongoing loss
of taxonomic experts. However, our understanding of how community composition based
on different taxonomic resolutions in soil organisms relates to management practices or to
functional characteristics in different farming systems is still scarce. The concept of taxo-
nomic sufficiency is based on the assessment of how much taxonomic information can be
given up, without losing characteristic response patterns of communities to anthropogenic
disturbance.
While there has been a lively debate and intense research on this topic over the last
decade in aquatic sciences (Maurer 2000; Terlizzi et al. 2003; Bevilacqua et al. 2009), the
subject is not as prominent in terrestrial systems or particularly in soil ecology. Three stud-
ies that focused on taxonomic sufficiency in comparing patterns of ant communities in
different habitats (Pik et al. 1999; Andersen et al. 2002; Schnell et al. 2003) suggested that a
coarser taxonomic resolution is sufficient as community composition differed between hab-
itats at all resolution levels. Báldi (2003) found a close correlation between diversity mea-
sures at different taxonomic levels in Diptera and Acari but did not analyze responses of