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).