Cover crops support the climate change mitigation potential of agroecosystems

are grown for the purpose of soil nutrient management, organic matter input, soil protection, and soil health improvement [5]. Cover crops are associated with multiple ecosystem services, such as closer nutrient cycling [5,6], activation of soil biology, biodiversity improvement [7], soil water management, and restoration of soil structures [8]. In addition, the mentioned effects of cover crops could mitigate climate change by soil carbon sequestration [9], biomass carbon storage, or reduced fertilizer losses to aquatic ecosystems. Recent studies show that these effects can lead to agronomic benefits that translate into higher yields and reduced agri- cultural input [10]. Despite these benefits, there exists a knowledge gap. The research problem addressed in this article is that there are no complete climate impact assessments of the cultivation of cover crops that also fully include land use effects. Cover crops reduces land use requirements by increasing yields of the subsequent crop. As land use change is still the largest carbon emis- sions source in the agri-food-system, yield increasing measures can be considered as a climate change mitigation option. According to Searchinger et al. [11], these carbon land benefits can be calculated as a “carbon opportunity cost,” which is the foregone carbon storage potential from natural vegetation to produce a certain agricultural product in kg CO2e kg-1. When yields rise on one piece of land, this carbon storage potential can be maintained or restored on other

locations since land use change is prevented or reverted. Kovak et al. [12] used this approach to quantify the climate change mitigation potential of a yield increase based on genetic modi- fied crops. This is the first study to include carbon opportunity cost in the evaluation of the cli- mate impact of cover cropping. As an additional climate benefit, cover crops remove carbon from the atmosphere during their growth while their residues and rhizodeposits are trans- formed to stable soil organic matter by retaining soil moisture. Further climate benefits of cover crops can be attributed to the supply of nutrients to the subsequent crop, which allows for fertilizer savings [13], reduced N2O emissions due to less nitrogen leaching, reduced solar radiation due to plant growth [14], and reduced soil erosion [15]. We define all factors above as “climate benefits”. While cultivating cover crops can accrue these climate benefits, it can also generate GHG emissions that we refer as “climate costs”. The cultivation of cover crops can increase N2O emissions in periods of anaerobic microbial conversion of cover crop decomposition products [16]. Emissions are also generated in the production of cover crop seeds through a number of avenues, such as the land required for seed production and the production process of the seeds. In addition, produced seeds need to be packed and delivered, which also generates emis- sions[17]. Lastly, tilling, seeding, and termination of cover crops requires the use of GHG

emitting machinery and resources [18]. Both climate benefits and climate costs of cover crops need to be carefully considered to calculate the NCCMI. This article addresses the research problem by developing a comprehensive framework to quantify the NCCMI of cover crops including land use effects based on a systematic literature review. Using selected keywords, a systematic search was conducted in “Web of Science” and “Google Scholar” and resulted in 1269 publications. We define a list of relevant climate bene- fits and climate costs from which the NCCMI of cover crops is derived. We apply the frame- work to cover crops for maize in the European Union (EU-27, which is all EU Member States excluding the United Kingdom) to quantify its total NCCMI. 2. Methods The following analyses are based on a typical Central European crop rotation, namely winter cover crops that are incorporated into the soil and maize as a cash crop following the cover crops in the spring. To quantify the impact of cover crop cultivation on the climate mitigation PLOS ONE Cover crops support the climate change mitigation potential of agroecosystems PLOS ONE | https://doi.org/10.1371/journal.pone.0302139 May 8, 2024 2 / 20 the Project "CATCHY", project number: 031B1060C. 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.