Cover crops support the climate change mitigation potential of agroecosystems

1000 to obtain the unit Mg CO2 -eq ha-1 [21]. Reduced N2O N ¼ EF5∗Reduced NLeaching ∗273 1000 2.5 Albedo change The reduced adsorption and thus increased reflection of solar radiation by cover crops’ plant cover compared to fallow land leads to a climate change mitigation effect. We found, however, only two studies evaluating the impact of albedo change from cover crops (Kaye and Quemada [22] and another by Carrer et al. [14]). 2.6. Nitrous oxide emissions In the case of nitrous oxide emissions, the cumulative emissions that occur during the period of fallow or the period from sowing to incorporation of cover crops are considered. The values with the unit kg N2O-N ha-1 were multiplied by a factor of 273 and 1000 to obtain the unit in Mg CO2e ha-1. 2.7. Foregone benefits due to cover crop seed land use The production of seeds for cover crops requires additional land that is not available for pro- duction of agricultural products. Land for these seeds cannot create the same carbon benefits [11] as alternative uses of this land. Therefore, this forgone carbon benefit needs to be added to the climate costs of cover crops. For this purpose, the yields of the four most common seed components of a cover crop mixture were determined in order to calculate the average land requirement for seed production of one hectare of cover crops’ seed mixture based on typical seeding rates. The following four species were selected to determine the land use for cover crops’ seed production: phacelia (Phacelia tanecetifolia Benth.), mustard (Sinapis alba L.), clo-

ver (Trifolium alexandrinum L.), and oats (Avena strigose Schreb.). Each of these cover crops has a 25% share in the final mixture of cover crops. A literature search on seed yields and aver- age seeding rates for these four species was conducted. The seed land use (SLU) for a specific cover crop was calculated per ha based on the following formula: SLU ¼ 1 n Xn i¼1 Ycc SRcc � � i; where Ycc is the yield in kg ha-1 of a specific cover crop and SRcc is the seeding ratio in kg ha-1. Table 2 shows the mean input values derived from the literature for the land use require- ments for cover crop seeds. The forgone carbon benefit of the land used for the production of cover crop seeds is deter- mined as follows: We assume that seeds for cover crops are produced in the European Union on land that would otherwise be used for wheat production since wheat is the largest crop in the EU by acreage. The carbon benefit (CB) of wheat is defined by Searchinger et al. [11]. Here, we assume that the carbon stock of land is not changing between wheat and seed pro- duction for cover crops and that there are no carbon benefits from bioenergy. The equation for CB is as follows: CB ¼ ðCOC þ PEMavg PEMEU Þ � Y where COC is the global carbon opportunity cost factor of wheat, PEMavg is the global average 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 5 / 20