Experimental design
We set up a field experiment as part of a series of multi-year
intercropping trials in 2019 close to Münster, Germany (51°58’32.5”N
7°33’57.4”E) and controlled crop diversity, crop species and management
intensity in a randomized split blocks design. Plots were sown in
monocultures and mixtures of summer wheat (Triticum aestivum L.),
faba bean (Vicia faba L.), linseed (Linum usitatissimumL.) and oilseed rape (Brassica napus L.) in mixed intercropping
in a substitutive design (Table S11). We used different sowing densities
for crop mixtures. For wheat, faba bean and linseed a 50/50 and 33/33/33
ratio was used in two- and three-species mixtures, while for oilseed
rape, due to its high competitiveness, a sowing density of 20% was used
in mixtures. A total of 104 plots each measuring 3x4 m were sown in four
replicate blocks with a sowing machine (Wintersteiger Plotseed S) at a
row spacing of 12.5 cm with 8 rows per m at a sowing depth of 3.5 cm on
May 14th in 2019. We assigned management intensity at
random to half-blocks: One half of each block received high intensity
management, made of one pre-emergence spray of herbicides (4.4 L/ha
Stomp Aqua with 455 g/L Pendimethalin as active agent) and nitrogen
fertilizer applied as a solution of urea and ammonium nitrate (70 kg
N/ha); the other half received no treatment (low intensity). We adjusted
application levels to the common amounts for our region, but reduced
fertilizer quantity to account for legumes in our mixtures. Crop mixture
and inherent levels of crop diversity were the lowest level of
replication and were assigned to random positions within each half-block
(Figure S2).
We used two different methods to sample arthropods: flower visitor
observations and pan traps for four different cropping systems: fallow,
no crop was sown (but weeds established especially under low intensity
management); crop monocultures; 2 species, two-species mixtures; and 3
species, three-species mixtures and for up to 13 different crop
mixtures, respectively. Note that flower visitor observations were
conducted on monocultures of wheat, bean and linseed and their two- and
three-species mixtures (eight levels), while pan traps were used to
sample arthropods on a wider range of crop mixtures, including mixtures
with oilseed rape (13 levels, Table S11).