Knowledge gaps in organic research: understanding interactions of cover crops and tillage for weed control and soil health

Abstract

Organic crop systems rely on tillage as the primary means to control weeds, but negative impacts of tillage may prevent farmers from achieving the potential soil health benefits of organic management. Cover crops have been suggested as a solution for overcoming this tillage trade-off directly by enhancing soil health and indirectly by providing weed control, thus reducing the need for tillage. In order to characterize the state of published research on the effects of cover crops on weed control and soil health in organic crop systems, we conducted a formal literature search on this topic and identified 116 relevant studies which were subsequently categorized by research focus, management strategy, and variables measured. We found 83 studies examined effects of cover crops on weed control and 33 studies examined effects of cover crops on soil health, but only 10 of the studies reported on both weed control and soil health effects. The lack of integrated studies examining both weed control and soil health responses to management highlights a research gap not sufficiently addressed by researchers, even though it is a topic of great interest to many organic farmers. A majority of studies (79) included reduced or no-till treatments, and annual grasses, clover, and vetch species were the most common cover crops. Assessments of aboveground biomass were the most common weed control measurements, while soil organic matter was the most common soil health measurement. Recommendations for future research needs include the following: more integrated assessments of the effects of cover crops on both soil health and weed control under varying tillage regimes; greater effort to characterize the soil health impacts of cover crop systems utilizing newly developed soil health indicators including soil physical parameters; long-term studies to assess dynamic soil health responses as well as perennial weed pressure (particularly in reduced and no-till organic systems); and greater allocation of research funding to regions outside of North America and Europe.