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containing a small amount of ethyl acetate. Suction samples were stored at −10°C and later
sieved and hand sorted using a dissecting microscope to separate animals from debris.
Functional grouping according to nematode feeding modes (six groups; Yeates et al. 1993),
spider-hunting strategies (nine groups; Uetz et al. 1999), and carabid-feeding mode (four
groups) or wing morphology (three groups) (Lindroth 1985, 1986; Luff 1998; Ribera 2001)
was based on the most comprehensive publications for each taxon.
Yield was estimated on 23 July from a center 1.7 × 10 m plot in each of the analyzed
fields. To measure the nitrogen content of wheat plants in each field, four grain samples
were bulked and dried at 80°C for 10 h, followed by a measurement of nitrogen content by
X-ray fluorescence (XRF) spectroscopy (for details, see Mäder et al. 2007). Potential nitrogen
mineralization rate in soil was determined by incubating 200-g soil samples at 20°C and
about 50% water-holding capacity for 6 weeks. Nitrogen mineralization rate was calcu-
lated from the increase in mineral N concentration between week 6 and week 2; data from
week 1 were excluded to reduce bias from sample handling (for mean values of ecosystem
functions, see
Table 5.1
;
for more details, see Birkhofer, Bezemer, et al. 2008).
Figure 5.1
exemplifies the differences in soil surface structure and wheat plant development between
CONMIN and BIOORG plots at the time of sampling.
The effect of different farming systems on the community composition of soil organ-
isms at different taxonomic resolutions was tested by analysis of similarities (ANOSIM;
Anderson et al. 2008). Prior to ANOSIM, all biotic data were log(
n
+ 1) transformed to
weigh down the importance of abundant species. Bray-Curtis distances were used to
a
b
c
d
Figure 5.1
Structural differences between (a) and (c) conventionally (CONMIN) and (b) and (d)
organically (BIOORG) managed plots at the time of sampling in the DOK trial, Switzerland, with (a)
and (b) showing differences in soil surface structure and (c) and (d) showing differences in wheat
plant growth in May 2005.
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