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

Authors: Osterholz, William - Will; CULMAN, STEVEN - The Ohio State University; HERMAN, CATHERINE - The Ohio State University; JOAQUIM DE OLIVEIRA, FRANCIELEN - The Ohio State University; PENATE, ALLISON - The Ohio State University; DOOHAN, DOUGLAS - The Ohio State University

Submitted to: Organic Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2020
Publication Date: 6/12/2020
Citation: Osterholz, W.R., Culman, S.W., Herman, C., Joaquim De Oliveira, F., Penate, A., Doohan, D. 2020. Knowledge gaps in organic research: understanding interactions of cover crops and tillage for weed control and soil health. Organic Agriculture. https://doi.org/10.1007/s13165-020-00313-3.
DOI: https://doi.org/10.1007/s13165-020-00313-3

Interpretive Summary: Organic crop systems rely on mechanical tillage as the primary means to control weeds, but tillage can also have negative soil health impacts. Cover crops planted in between main cash crops have been suggested as a solution for overcoming the trade-off between soil health and weed control caused by tillage. We conducted a formal search of the scientific literature and found over 100 relevant studies. The studies were categorized to characterize their main focus and experimental methods in order to identify gaps in scientific understanding. We found 81 studies that examined effects of cover crops on weed control, 21 studies that examined effects of cover crops on soil health, but only 13 of the 117 studies reported both weed control and soil health effects. The small number of studies examining both weed control and soil health effects of cover crops highlights an under-addressed gap in the research, even though it is a topic of great interest to many organic farmers. Recommendations for future research needs include: more integrated assessments of the effects of cover crops on both soil health and weed control; greater effort to characterize the soil health impacts of cover crop systems utilizing newly developed soil health indicators; long-term studies that can monitor slow changes in soil health and perennial weed pressure; and greater attention to organic agriculture in regions outside of North America and Europe.

Technical Abstract: Organic crop systems typically utilize tillage as the primary means of weed control, but negative impacts of tillage may prevent farmers from achieving the soil health goals 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 117 relevant studies which were subsequently categorized by research focus, management strategy, and variables measured. We found 81 studies examining effects of cover crops on weed control, 21 studies examining effects of cover crops on soil health, but only 13 of the 117 studies reported on both weed control and soil health. 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 (80) 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: More integrated assessments of the effects of cover crops on both soil health and weed control; 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.