Cover crops support the climate change mitigation potential of agroecosystems

production emissions for wheat, PEMEU is the European Union’s production emissions for wheat, and Y is the average wheat yield in the European Union (based on data from 2011 to 2022 for the EU-27 [23]). COC, PEMavg, and PEMEU are from Searchinger et al. [11]. For PEMEU, we used the production emissions for wheat in Sweden, since no European average values were available. The forgone carbon benefits due to seed land use can be calculated by multiplying SLU and CB. 2.8. Production emissions for cover crop seed production, dispatch and additional machinery costs Product emissions for cover crop seed production are not available in literature and therefore derived from maize, rapeseed, and spring wheat seed production. This is a conservative assumption since the nitrogen input and machinery operations as key drivers of emissions are usually higher in these crops than in cover crops. Emissions data is collected from the literature in kg CO2e kg-1 of seed and is multiplied with the seeding rate of cover crops. This results in an emissions value per hectare. Emissions for processing, packaging, and transporting cover crop seeds are also not avail- able and derived from maize seed production emissions and are expressed in kg CO2e kg-1 of seed. This is again a conservative assumption since maize seed has to fulfill much higher qual- ity standards than cover crop seed. The emissions of additional machinery operations for tillage, seeding, and mechanical ter- mination of cover crops were included only in terms of additional diesel fuel usage. Average

diesel fuel consumption of all additional operations was calculated and multiplied by the aver- age GHG emissions of diesel fuel. 3. Results The impact of all analyzed factors on the NCCMI of cover crops is summarized in Table 3. The results refer to a typical European crop rotation using a winter cover crop and maize Table 2. (Continued) EU-27 average per hectare (ha) EU-27 total Unit Mean Low (-95% confidence level) High (+95% confidence level) Unit Mean Low (-95% confidence level) High (+95% confidence level) Net climate change mitigation impact of cover crops Mg CO2e ha-1 3.30 0.74 6.14 1,000 Mg CO2e 49,795.58 10,911.32 94,615.78 Share of EU-27 agriculture emissions in 2020 13.0% 2.9% 24.7% Note: Calculation, formulas and number of studies are provided as supplementary material (S1 File). ha is hectares. EU-27 is the 27 Member States of the European Union (all Member States excluding the United Kingdom). https://doi.org/10.1371/journal.pone.0302139.t002 Table 3. Impact factors of cover crops on climate change mitigation analyzed in this study, source: Own table. Climate Benefits Climate Costs • Carbon land benefit based on yield gain • N2O emissions • Carbon sequestration • Foregone benefits due to cover crop seed land use • Nitrogen fertilizer savings • Production emissions for cover crop seed production • Reduced indirect N2O emissions due to less leaching • Processing, packaging, and transport of cover crop seed • Albedo change • Additional machinery operations https://doi.org/10.1371/journal.pone.0302139.t003 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 7 / 20