Agricultural expansion and intensification have boosted global food production but have come at the cost of environmental degradation and biodiversity loss. Biodiversity-friendly farming that boosts ecosystem services, such as pollination and natural pest control, is widely being advocated to maintain and improve agricultural productivity while safeguarding biodiversity. A vast body of evidence showing the agronomic benefits of enhanced ecosystem service delivery represents important incentives to adopt practices enhancing biodiversity. However, the costs of biodiversity-friendly management are rarely taken into account and may represent a major barrier impeding uptake by farmers. Whether and how biodiversity conservation, ecosystem service delivery, and farm profit can go hand in hand is unknown. Here we quantify the ecological, agronomic and net economic benefits of biodiversity-friendly farming in an intensive grassland-sunflower system in southwest France. We found that reducing land-use intensity on agricultural grasslands drastically enhances flower availability and wild bee diversity, including rare species. Biodiversity-friendly management of grasslands furthermore resulted in an up to 17% higher revenue on neighboring sunflower fields through positive effects on pollination service delivery. However, the opportunity costs of reduced grassland forage yields consistently exceeded the economic benefits of enhanced sunflower pollination. Our results highlight that profitability is often a key constraint hampering adoption of biodiversity-based farming and uptake critically depends on society’s willingness to pay for associated delivery of public goods such as biodiversity.

Species richness and abundance data on bees were collected in 2015 in 21 pairs of grasslands and adjacent sunflower fields in southwestern France. In each grassland and sunflower field, bees were surveyed in two 150 m² transects, with a total of 15 min net surveying time per transect. Sunflower fields were sampled in two survey rounds during sunflower bloom; grasslands were sampled twice just before and twice shortly after sunflower bloom.  All entomophilous plant species that flowered during the grassland surveys were recorded and their flower cover was estimated as the total number of flower units × the mean surface area of the flower unit, divided by the transect area. Total flower cover per transect was determined as the sum of the cover of all observed flowering species.

The contribution of insect pollination to sunflower crop yield was assessed using pollinator exclusion treatments. Prior to anthesis, ten pairs of sunflower plants were selected in each field, with the pairs evenly distributed along a 45 m transect perpendicular to the crop edge. One plant of each pair was randomly selected and its flower head was covered with a fine mesh nylon bag (<1 mm × 1 mm), allowing self- and wind-pollination but excluding insect-pollination. The flower head of the other selected plant was not bagged and remained accessible to all flower-visiting insects. All bags were removed after sunflower bloom. After harvest, flower heads were dried for 72 hours in a ventilated heat chamber at 37°C, and seeds were removed from the flower heads using a threshing machine (Criquet, Moulis). Full seeds were dried at 80°C for 48 hours. Full seeds were counted and weighed using an automatic counter and an electronic balance, respectively.

Varietal differences in pollination-dependency and crop yield were quantified in a pot experiment at Wageningen University Experimental Farm (the Netherlands) in the summer of 2016. Seeds of the different varieties were grown outdoors under ambient conditions in 11 l pots. Plants were drip irrigated and received 50 kg ha^-1 of nitrogen fertilizer. Five experimental randomized blocks were established, with each block containing a pair of plants of each variety. Just before anthesis, a randomly selected plant of each pair received a pollinator exclusion treatment (1 mm x 1mm fine mesh nylon bag), using the same approach as in the field study (see above). Pollinator visitation rates on open-pollinated plants were monitored for a total of 60 minutes on two occasions during sunflower bloom (30 min each). After harvest, flower heads were dried for three weeks at 35°C. Seeds were manually extracted and sorted. Dry full seeds were counted using a seed counter and weighed using an electronic scale.

Early 2016 semi-structured interviews were used to survey the farmers participating in the study to obtain information on characteristics and agronomic practices on the sunflower fields and grasslands. Agronomic information obtained included sunflower variety, sunflower field size, sunflower total nitrogen fertilizer application (organic and inorganic), grassland sowing year (age), sown forage plant species, grassland harvesting frequency (number of harvests in 2015) and grassland size.