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

Abstract Organic farmingis gaining importance in view of its beneficial effects on soil quality, environmental performance and biodiversity. However, it is still unclear how organicmanagement performs over time and whether the duration of organicmanagement influences crop yieldand 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 organicmanagement affected crop yield, weed cover, soil fertilityand biodiversity as well as the overall system performance, assessed as ecosystem multifunctionality. Maize yield (-6.0%) and wheat yield (-22.2%) decreased in organiccompared to conventional fields. However, the duration of organicmanagement did not affect crop yield. There was also no effect of the duration of organicmanagement on weed cover but it was much higher under organicmanagement, with mean values of 33.0% in organiccompared to 2.0% in conventional fields in maize, and 13.4% compared to 1.2% in wheat, respectively. Soil fertilityand microbial activities were not significantly different between management practices, which might be due to the large variation among fields. Root colonization of arbuscular mycorrhizal fungiincreased (+19.7%) under organicmanagement in wheat. Overall, this study demonstrates a rapid shift of agro-ecological functions after conversion to organic farmingand that the duration of organicmanagement has no impact on crop yield, weed cover and soil fertility.