Vincent de Leijster

69 Almond farm profitability under agroecological management 4 combined price premiums and public greening payments to explore mutual effects on the NPV. For all these analyses the discount rate was kept constant at 5%. 4.2.5 Payments for environmental services (PES) We explored the financial compensation for the environmental externalities related to soil carbon stocks and soil erosion, as these are considered externalities with the strongest effect on biophysical land degradation in the region (Montanaro et al., 2017). First, we evaluated compensation for stored organic carbon in the soil through valuing treatment specific soil carbon stocks using the voluntary carbon market price and the EU Emissions Trading System carbon price (EU-ETS; Zhang and Wei, 2010). Additionally, we calculated the externality costs of erosion by valuing the treatment-specific on-site and off-site costs of soil loss due to water erosion. For this part of the study CM was not included in the analyses due to absence of information on its long-term effects on SOC and soil erosion. The value of soil organic carbon stocks (SOC) is given as the value for the net carbon gain that is generated over the full lifetime of the project (30 years). We assumed that the SOC stocks would increase with 46% for NT and with 34% for GM compared to CT, which is reported by Cucci et al. (2016) after a 35 yearlong experiment in an Italian almond plantation with similar treatments. No comparable long-term study was found for compost application, so this was not considered for this part of the analysis. We assumed a baseline SOC level of 8.4 tC ha -1 for the reference situation, CT, as reported in De Leijster et al. (2019). The value per ton carbon on the voluntary carbon market was assumed to be €5.54 ($5.1; European Central Bank Currency Converter, 14-08-2019), which is reported by the Ecosystem Marketplace as the average voluntary market carbon price for carbon stored in forestry and land-use projects (Hamrick and Gallant, 2017). With an increase of 46% in SOC, the soil organic carbon stock of NT has an added value of €21.41 ha -1 over 35 years and that of GM with an increase of 34% in soil organic carbon an added value of €15.82 ha -1 . This corresponds to an annual income of €0.61 for NT and €0.45 for GM, when the stored carbon is traded on the voluntary carbon market. The carbon value of the EU-ETS is higher and was assumed to be €20, which was the average price in 2019 (Marcu et al., 2019) and corresponded to an annual income of €2.21 ha -1 y -1 for NT and €1.63 ha -1 y -1 for GM. The externality costs for erosion were calculated based on average European costs of erosion, as calculated by the EU (Görlach et al., 2004). The latter study reports average on- site private costs of €9.83 ha -1 y -1 (based on €7.56 ha -1 y -1 in 2003 with correction for inflation between 2003-2019), which included projected yield losses as a result of reduced nutrient balance, organic matter content and plant rooting depth in the farms’ soil. Additionally,