Fertilization using manure minimizes the trade-offs between biodiversity and forage production in agri-environment scheme grasslands

plant communities, we compared plant Shannon-Weiner diversity index, forb species richness and nectar productivity. For insect communities we compared the abundance of bumblebees, the Shannon-Weiner diversity index of pollinators, leaf miners and parasitoids, and the per- centage of herbivores attacked by parasitoids. For forage we compared the mean dry weight of forage in the years 2011–2014 as a measure of yield; and three measures of nutrient content: ash, crude protein and ruminant metabolizable energy. These indicators were based on infor- mation from the following surveys: a vegetation survey from 2014 [34] and forage productivity data for the period 2011–2014 [35]; insect and flower surveys from 2016 [33]; and field sam- pling of forage collected for this study in 2017. While these datasets were gathered in different years, they were all collected towards the end of a 27-year experiment known to have exerted strong, detectable cumulative impacts on the vegetation [33], and so differences across treat- ments were expected to be larger than year-to year variations. Data collection and indicator descriptions are as follows: Plant community For plant diversity and forb species richness: we used data from an existing vegetation survey, that recorded plant species and percent cover within 2 x 2 m quadrats [34]. Information on the number of species and on percent-cover were then used to estimate the Shannon-Weiner diversity index. For nectar productivity, we combined data on flower abundance from 2016 [33] and nectar

quantity per species from literature [36]. Flower abundance was collected by counting all flow- ers within three transects of 30 cm x 5 m lengthwise. Sampling took place in 2016 during late May to early June and again 3 weeks later for a total of two rounds. To estimate nectar produc- tivity, we multiplied the amount of nectar produced by one flower of each of the species by the total number of flowers of the species found in the plot. We then calculated the total amount of nectar for each plot by summing the amount of nectar produced by all the species recorded in each plot. Table 1. Individual indicators describing the plant community, insect community and forage. Indicator Description Plant community Diversity of plants Shannon-Weiner index. Forb species richness Number of forb plant species Nectar productivity Estimated μl of nectar produced by the total number of forbs present in each plot. Insect community Abundance of Bombus spp. Number of observations of bumblebees feeding on the plots. Diversity of herbivores Shannon-Weiner index Diversity of parasitoids Shannon-Weiner index Diversity of pollinators Shannon-Weiner index Percent parasitism Proportion of emergences parasitoids from the total leaf miner emergences. Forage Ash Organic matter content. Crude protein Measurement of nitrogen supply from the forage. Ruminant metabolizable energy Energy available for supporting metabolic processes and for growth or reproduction after accounting for losses in digestion, gases and urine. Mean dry matter (2011– 2014)

Yield of biomass per m2 following drying to constant weight. https://doi.org/10.1371/journal.pone.0290843.t001 PLOS ONE Manure minimizes trade-offs between biodiversity and forage production in agri-environment scheme PLOS ONE | https://doi.org/10.1371/journal.pone.0290843 October 4, 2023 4 / 18