Metadata for ’Data from: Undersowing oats with clovers supports pollinators and suppresses arable weeds without reducing yields’ We studied the effects of undersowing oats with a mixture of three annual clovers species across different aspects of cropping system multi-functionality using 26 observation plots in a paired field design with 13 fields. We investigated 16 below- and aboveground ecosystem service indicators related to soil mineral nitrogen, arable weed control, pollination, disease and pest pressures, natural pest control and crop yield. We measured each of the 16 ecosystem service indicators in an intercropped and in a control treatment with identical management. Some indicators were measured before and after the experiment in both treatments to assess the magnitude of change by the treatment. For further information, see methods in the publication Boetzl et al. (2023) Undersowing oats with clovers supports pollinators and suppresses arable weeds without reducing yields. Journal of Applied Ecology. The data in the 'combined_dataset.csv' file have information on different ecosystem service indicators collected in 13 fields ('field_ID') and two treatments per field (intercropped and control). 27 rows. In three fields ('field_01', 'field_06' and 'field_11') some assessments could not be done due to different local reasons and the corresponding cells thus state 'NA' (not available; for more information see Boetzl et al. (2023)). Measurements in 'area_treatment_m2' and 'clover_biomass_dry_weight_g' only refer to the intercropped treatment and 'NA' (not available) is stated for the control treatment. field_ID: ID of the sampled field, treatments with the same filed_ID were nested within the same field treatment: two treatments per field, ‘intercropped’ = oats with an undersown mixture of three different annual clover species, ‘control’ = only oat, both treatments are managed identically within each field area_treatment_m2: area of the intercropped treatment in each field in m2 area_field_m2: total area of each field in m2 arable_land_cover_proportion: proportion of land covered by arable land-use in 1km radius around the observation plots in each field clover_biomass_dry_weight_g: biomass of clover at the point of oat harvest in g (dry weight) per m2 soil_mineral_nitrogen_before: soil mineral nitrogen in soil samples in spring before our experiment in kg per ha soil_mineral_nitrogen_after: soil mineral nitrogen in soil samples in spring after our experiment in kg per ha arable_weed_cover_proportion: proportion cover of arable weeds measured on 12 m2 arable_weed_biomass_dry_g: biomass of arable weeds at the point of oat harvest in g (dry weight) per m2 root_disease_severity_before: root disease severity index measured on Trifolium pratense grown in soil taken before the experiment root_disease_severity_after: root disease severity index measured on Trifolium pratense grown in soil taken after the experiment root_feeding_nematodes_before: root-feeding nematodes extracted from soil taken before the experiment, individuals per g dry soil root_feeding_nematodes_after: root-feeding nematodes extracted from soil taken after the experiment, individuals per g dry soil predatory_nematodes_before: predatory nematodes extracted from soil taken before the experiment, individuals per g dry soil predatory_nematodes_after: predatory nematodes extracted from soil taken after the experiment, individuals per g dry soil cereal_leaf_beetle_damage_proportion: proportion of damage to oat plant leaves caused by cereal leaf beetles (Oulema melanopus) [percentage] flower_cover_cm2: total flower area in cm2 per m2 pollinator_count: number of observed pollinator individuals predation_rate_proportion: proportion of consumed aphids on aphid cards on the soil level (i.e. predation rate) [percentage] pitfall_trap_sampling_days: days of active pitfall traps, the number differs between treatments and fields as some traps were lost, this has to be accounted for when densities are compared carabids_predatory_count: number of carabid beetles belonging to predominantly predatory species in the pitfall traps carabids_granivorous_count: number of carabid beetles belonging to predominantly granivorous species in the pitfall traps staphylinids_count: number of staphylinid beetles in the pitfall traps spiders_count: number of spiders in the pitfall traps oat_kg_yield_per_ha: oat yield calculated as kg per ha N_g_per_kg_dry_weight_oat_yield: nitrogen content in the oat yield measured as g nitrogen per kg oat yield (dry weight)