Vincent de Leijster

75 Almond farm profitability under agroecological management 4 4.4.1 Management regimes and yields Our findings show that NT and GM produced lower yields than CT (reduction in yields of NT and GM of 16% and 11% on average (Appendix Figure A4-1&2), and CM produced higher yields than CT. Giller et al. (2009) suggest that NT requires a minimum transition period of 10 years, after which it will be able to produce similar yields as CT. In the current study we used yield data obtained from short-term (3 year) field experiments to make long-term financial projections. According to Giller et al. (2009) yield levels can change over larger time spans after implementation of new management, therefore our short-term experiment may have missed these developments. However, previous studies in Mediterranean European almond plantations showed contrasting results to what Giller et al. (2009) suggest, as they found over a longer time scale (10-12 years) larger yield gaps for NT (-63% and -28%) compared to our short-term study (De Giorgio and Lamascese, 2005; Martin-Gorriz et al., 2020; Martínez- Mena et al., 2013). One of these studies, an agroecological almond experiment in the same Spanish study region as ours observed declining yields for NT in the first 7 years after implementation followed by stabilization of yields until the 10 th year, at a level of 85% lower than CT (Martínez-Mena et al. unpubl., pers. comm.). This indicates that the production in the NT treatment of our experiment could decrease further in the following years, increasing the opportunity costs. The lower yields in the GM treatment are, however, not in line with earlier findings that reported no significant yield differences compared to CT (De Giorgio and Lamascese, 2005; Martin-Gorriz et al., 2020). Apparently, when NT is applied it results in a trade-off between farm profitability and ecosystem services provisioning, since we demonstrated earlier that NT management increased ecosystem service supply (e.g. nutrient cycling, understory plant diversity and understory carbon stock) compared to CT (De Leijster et al., 2019). The implementation of CM, on the other hand, rehabilitated nutrient cycling and carbon stock, and also provided higher economic returns than CT. Therefore, CM provides a bundle of ecosystem services and can be implemented without external financial support. In this study, the vegetation covers in the NT treatment covered the experimental plot entirely and for GM a 1.5 m strip from the almond trunks was kept bare while the remainder of land was sowed (approximately 5 m wide). Another study on vegetation cover management in peach orchards in North Carolina (USA) demonstrated that there was a negative correlation between the proportion of soil that was covered by vegetation and peach tree productivity, with higher production at less vegetation cover (Fisk et al., 2015). There might be similarities between the responses of almonds and those of peaches to vegetation cover. Therefore, we suggest that further research is needed to identify whether other vegetation cover practices, such as narrow vegetation strips in the middle of alleys