Long-term feasibility of reduced tillage in organic farming

Summary

Agricultural practices, and mainly soil tillage, highly contribute to the emissions of greenhouse gases such as CO2 and N2O. Reducing the tillage improves the quality of the soil and may help mitigating the greenhouse emissions. In Europe, approximately 25 % of the arable land is managed under reduced tillage practices, including both notill and reduced tillage. However, they have been developed mainly in herbicidemanaged systems. The potential increase in weed infestation caused by the lack of soil inversion may threaten crop yields, and is one of the major drawbacks for the adoption of reduced tillage among organic farmers. We report the results from a field experiment comparing the reduced tillage with respect to the conventional tillage in the long-term, in terms of crop production and weed flora, with special attention provided to perennials and grasses, which are more difficult to control. The experiment commenced in 2002 in Switzerland and data on yield, cover, richness and composition of the weed flora were collected for wheat (2003 and 2009), sunflower (2004 and 2010) and spelt (2005 and 2011) through two complete rotations. We found that weed abundance was 2.3 times higher under reduced tillage, but we did not observe an increasing tendency over the years. However, the average abundance of perennials almost doubled over time under reduced tillage, thus changing the community composition between tillage systems. Nevertheless, yields did not differ between tillage systems. This is the first long-term trial under organic management showing that reduced tillage provides an actual opportunity to improve the environmental performance of this cropping system. Reduced tillage did not affect yields compared with conventional tillage and maintained the weed flora within acceptable levels in a 10-year trial. However, the management of perennials is still a challenge for the overall sustainability of these practices over time.