Agriculture Reference
In-Depth Information
and by the use of biodynamic preparations (horn-manure and horn-silica; see Mäder et al.
2000 for further details). Crop rotation and soil tillage regime were identical for all 5 × 20
m plots. Synthetic insecticides were last applied in 2001 in the conventional systems, and
soils of the CONFYM and CONMIN system were treated with a molluscicide in 2003 and
2004. A single herbicide containing the active ingredients carfentrazone and isoproturon
was applied to winter wheat in both conventional systems on 1 April 2005, and the growth
regulator trinexapac-ethyl was applied on 22 April 2005. The two conventional systems
received a total of 90 kg N ha
−1
as calcium ammonium nitrate in March and April 2005;
BIOORG received a total of 44 m
3
slurry ha
−1
in two rates (N
tot
77.9, N
min
33.2, organic matter
1,335 kg ha
−1
); and BIODYN received 30 m
3
ha
−1
(N
tot
46.2, N
min
28.5, organic matter 651 kg
ha
−1
) only once (for further details on the DOK trial, see Mäder et al. 2002 and Fließbach
et al. 2007).
All four replicated wheat plots of each farming system were sampled on 9 May 2005
by collecting one small soil core (8-cm diameter, 5-cm deep) and one sample of bulk soil (1
kg) from the upper 5-cm layer of randomly chosen locations at the northern and southern
end of each of the 16 plots (minimum edge distance 1.5 m,
N
= 32). Bulk soil was used to
analyze chemical soil properties, FA profiles, and nematode communities; soil cores were
sampled to analyze enchytraeid communities. Soil pH was measured in 0.1
M
KCl solution
in a soil-to-liquid ratio of 1:3 (w/v). Total soil nitrogen and carbon were measured using an
elemental analyzer (Carlo Erba, Milan, Italy) and were taken to represent total soil nitro-
gen content (N
tot
) and soil organic carbon content (C
org
) as concentrations of carbonates are
low at the study site. To measure soil water content (SWC), fresh soil samples were dried
Birkhofer, Bezemer, et al. 2008).
Lipid extractions for analysis of PLFAs and NLFAs (neutral lipid fatty acids) were
made on 3 g of fresh soil according to the work of Frostegård et al. (1993) and Hedlund
(2002). The resulting FAMEs were separated on a Hewlett-Packard 6890 gas chromato-
graph. Relative retention times of the FAMEs were compared to those of standards (for
more details, see Birkhofer, Bezemer, et al. 2008). The classification of FAs into functional
groups was based on published references (Frostegård and Bååth 1996; White et al. 1996;
Olsson 1999; D'Angelo et al. 2005): gram-positive bacteria at i14:0, i15:0, a15:0, i16:0, i17:0,
and a17:0; gram-negative bacteria at 16:1ω9, 16:1ω7c, 16:1ω7t, and 18:1ω7; sulfate-reducing
bacteria at 10Me16:0, cy17:0, 10Me17:0, 10Me18:0, and cy19:0; NLFA 16:1ω5 at AMF; 18:2ω6 at
nonmycorrhizal fungi.
The total number of nematodes was counted, and a minimum of 150 nematodes was
further identified to family or genus level according to Bongers (1988) and classified into
different feeding groups according to Yeates et al. (1993). Enchytraeids were extracted from
soil using a combination of cold and hot wet funnel extraction methods to maximize the
extraction efficiency. Soil samples were first submerged in cold water for 24 h in a plastic
sieve (Dunger and Fiedler 1997) and later heated for 3-4 h in a wet funnel (O'Connor 1955).
All individuals were identified to species or genus level.
To estimate densities of soil-dwelling generalist predators (Araneae and Carabidae),
an area of 2.0 m² was fenced (PVC [polyvinyl chloride] barriers; 50 cm high, 10 cm sunk
into the soil), and four pitfall traps containing a water detergent mix were placed along the
inner barrier and left open for 14 days (3 to 17 May). Pitfall samples were transferred to 70%
ethanol, sieved, and later hand sorted. Vegetation-living spiders were sampled on 16 May
under dry conditions using an Eco-Vac insect suction sampler (EcoTech, Bonn, Germany).
An area of 0.7 m² was fenced on each of the two sides of each plot (PVC barriers 50 cm
high) and immediately suction sampled for 90 s. Samples were transferred to glass vessels
Search WWH ::
Custom Search