Crop yield, weed cover and ecosystem multifunctionality are not affected by the duration of organic management

Organic farming is gaining importance in view of its beneficial effects on soil quality, environmental performance and biodiversity. However, it is still unclear how organic management performs over time and whether the duration of organic management influences crop yield and ecosystem functioning. Here we compared 34 fields in Swiss farms assigned to four groups: 1) conventionally managed farms; 2) farms in transition to organic farming (in the 1st – 3rd year); 3) farms converted moderately long ago (9–13 years); and 4) farms subjected to long-term organic farming (15–32 years). We selected one field per farm and examined in two subsequent years whether management practices (conventional vs. organic farming) and the duration of organic management affected crop yield, weed cover, soil fertility and biodiversity as well as the overall system performance, assessed as ecosystem multifunctionality. Maize yield (-6.0%) and wheat yield (-22.2%) decreased in organic compared to conventional fields. However, the duration of organic management did not affect crop yield. There was also no effect of the duration of organic management on weed cover but it was much higher under organic management, with mean values of 33.0% in organic compared to 2.0% in conventional fields in maize, and 13.4% compared to 1.2% in wheat, respectively. Soil fertility and microbial activities were not significantly different between management practices, which might be due to the large variation among fields. Root colonization of arbuscular mycorrhizal fungi increased (+19.7%) under organic management in wheat. Overall, this study demonstrates a rapid shift of agro-ecological functions after conversion to organic farming and that the duration of organic management has no impact on crop yield, weed cover and soil fertility.