Vincent de Leijster

51 Agroecological management improves ecosystem services in almond orchards within one year 3 We found higher enzymatic activity in NT than CT, but lower soil total N and extractable P contents and leaf N and P contents. Another study in a Spanish almond system also found that by comparison with CT, NT resulted in higher enzymatic activity for dehydrogenase (+37%), β-glucosidase (+93%) and phosphatase (+87%). However, in contrast with our latter findings, lower soil and leaf nutrient levels in NT than in CT, the studies by Ramos et al. (2011) and Cucci et al. (2016) report higher soil N content for NT than for CT. The relationship between NT and soil N content seems to be variable, as Martínez-Mena et al. (2013) did not find differences between NT and CT in almond orchards, and Gomez et al. (2009) reported a reduction in soil N content with NT in olive orchards. Martínez-Mena et al. (2013) propose that NT increases soil compaction, which reduces both the N-mineralization rate in the soil and crop root development, which in turn reduces nutrient uptake by the plant. This might explain the lower N content in the soil and almond leaves in NT in our study, but as we did not measure physical properties of the soil, we could not investigate this. CM is known to have the capacity to improve the soil’s physical and biological properties such as soil structure, water-holding capacity and macrofauna (Norris and Congreves, 2018; Ouédraogo et al., 2001), which, in theory, could offset the disadvantages of NT. A study in Mediterranean apricot orchards showed that applying CM and NT together can effectively restore soil nutrient contents but not SOC levels (Montanaro et al., 2010). More research on the combination of the considered agroecological treatments is needed to assess its effect on the nutrient cycling capacity. Carbon stock We found that the carbon stock in the agroecological treatments was 8–76% higher than in CT. Unsurprisingly, GM resulted in the highest carbon stock levels in the understory compared to CT. This is because GM plots received additional biomass from the seeded common vetch, bitter vetch and barley, whereas in CT the understory was removed. Our results are in line with the results of a 35-year-long study on almond orchards in Italy, which reported that green manure application increased carbon stock in the understory by 9% as compared to conventional tillage (Cucci et al., 2016), but we found a much larger increase. However, there seems to be a relation with water availability as reported by Ramos et al. (2009), who found that in years with more dry periods the understory in NT stores more carbon than in GM, while this is the reverse in years with less water limitation. Cucci et al. (2016) also found 34% higher SOC for almonds with GM than for CT, which we did not observe, on the contrary we found lower SOC contents for GM and NT compared to CM and no differences with CT. Vicente-Vicente et al. (2016) showed, in a meta-analysis on soil carbon sequestration