Long-term feasibility of reduced tillage in organic farming

Agricultural practices such as soil tillage emit greenhouse gases such as CO2 and N2O. As a consequence, reducing the tillage could both reduce greenhouse emissions and improve soil quality. In Europe about 25 % of arable land is managed under reduced tillage and no tillage, mainly using herbicides to get rid of weeds. Therefore, a major drawback for organic farmers is that the lack of herbicide and soil inversion could increase weed infestation. Here, we compared reduced tillage and conventional tillage in a 2002-2011 field experiment under organic management in Switzerland. We analyzed crop production and weed flora, with a focus on perennials and grasses. Data on yield, cover, richness, and composition of the weed flora were collected for wheat in 2003 and 2009, sunflower in 2004 and 2010, and spelt in 2005 and 2011, through two complete rotations. We found that weed abundance was 2.3 times higher under reduced tillage, though we did not observe a systematic increase with time. The average abundance of perennials almost doubled over time under reduced tillage, thus changing the community composition between tillage systems. Despite the weed increase, yields were similar for reduced tillage and conventional tillage. As a consequence, this study represents the first long-term trial under organic management showing that reduced tillage improves the environmental performance of this cropping system.