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

Introduction Intensive agriculture is a significant cause of the decline in biodiversity in general, and a known driver of insect declines [1]. This decline in insect populations threatens ecosystem ser- vices like pollination and pest control, which are essential for both biodiversity and agriculture [2–4]. Although, agricultural practices such as organic farming and agri-environmental schemes have been proposed and implemented, the uptake and efficacy of these options have not been sufficient to stop biodiversity loss [5]. This problem is partly due to gaps and biases in the evidence needed to achieve effective management and inadequate consideration of farm- er’s need to maintain a viable business [see 6–8]. Many grassland ecosystems have their origins in an ancient agriculture created by humans and their livestock and these habitats have become highly diverse under centuries of human management [9]. In the last century, traditional practices like addition of manures and low grazing levels have been replaced by modern agriculture that uses high levels of mineral fertil- izers and reseeding with productive forage grasses to allow higher grazing rates [10]. This change has contributed significantly to widespread habitat and biodiversity loss, with the loss of up to 97% of the original coverage of seminatural grasslands in Europe [11]. This high loss in cover has led to a considerable interest in preserving the remaining areas and restoring areas under intensive agricultural practices. [12,13]. Most proposed restoration actions are

wildlife-friendly practices such as: a) replacing application of mineral fertilizers with organic manures, b) stopping all fertilization, c) reducing grazing intensity and d) using livestock with lower nutritional needs [14–16]. Although, there is consensus that reducing grazing intensity is necessary [15,17,18] reducing nutrient inputs is more complicated, since fertilizers are not only applied to increase biomass but also to meet livestock nutritional needs [see 19,20]. More- over, despite evidence that using hardy or native types of livestock (breeds) at low intensity can be an effective farming approach ([e.g. 21], it is far from being a widespread approach. There is good evidence that increasing plant diversity affects livestock production posi- tively; for example, it can increase yield [22] and forage from species-rich grasslands can be of greater nutrient value than cereals and conventional forage [23]. Likewise, trade-offs of man- aging land for conservation or production have been widely discussed under the idea of multi- functionality of ecosystems e.g., [24,25] and within the land sharing vs land sparing debate [26–28]. Nevertheless, there is little empirical evidence on how restoring and preserving grass- lands using different fertilization regimes, including that of no-fertilizer, could benefit biodi- versity and livestock production simultaneously. Recent evidence shows that, at the landscape level, the productivity of grasslands and con- servation of arthropods can potentially be improved without reducing production or jeopar-

dizing conservation objectives [29]. Recent work also shows that the optimum for production and conservation can be potentially achieved by a combination of land sharing and land spar- ing strategies across the landscape [27,28]. Although, these studies offer important insights for maintaining biodiversity in agricultural systems, most of them measured productivity using yield without considering the fact that productivity also depends on the nutritional quality of forage e.g., [6]. Low levels of mineral and manures are allowed under agri-environmental schemes. Under such schemes, even low fertilizer loads can inhibit the establishment of target plant species, thus hindering the restoration of grasslands without a significant improvement in production [12]. Indeed the critical load for nitrogen in European low and medium altitude meadows was recently confirmed at 20–30 kg N ha-1 yr-1 a range above which increase in grass and loss of diversity is expected [30]. Nevertheless, subsides provided to address the loss of yield consis- tent with reduced inputs are sometimes insufficient to compensate for income forgone [26]. 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 2 / 18 doi:10.5061/dryad.vmcvdncr3). All relevant data are within the manuscript and its Supporting Information files. Funding: "Project was partly funded by Bristol Centre for Agricultural Innovation (BCAI, project no.42). https://www.bristol.ac.uk/biology/bcai/ EVG

was funded by a grant from CONACYT, Mexico for graduate studies (381429). https://conacyt.mx SMS was supported in part by the UK-SCaPE program delivering National Capability (NE/ R016429/1) funded by the Natural Environment Research Council. https://www.ukri.org/councils/ nerc/" The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript." Competing interests: The authors have declared that no competing interests exist.