Killing cover crops mechanically: Review of recent literature and assessment of new research results

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Abstract
Cover-crop residues left on the soil surface as a mulch in no-till crop production systems protect the soil from erosion, increase water infiltration and suppress weeds. Because many growers using cover crops want to reduce chemical inputs, non-chemical methods of killing or suppressing cover crops are needed. In the first part of this paper we review the current literature and discuss advantages and disadvantages of five mechanical methods for killing cover crops, i.e., mowing, rolling, roll-chopping, undercutting and partial rototilling. We also report on three new studies that broaden the current literature, including planting into freshly killed residue. In the first study, the use of planter attachments to remove surface residues from the planter row improved stands when cotton was no-till planted 2–7 days after mowing cover crops in Mississippi. In the second study, 100% of a rye/vetch cover crop in Missouri was killed by mowing, and greater than 90% was killed by roll-chopping. Cotton stands were reduced by the use of row cleaners that clogged when the cover crop was roll-chopped or mowed on the same day that the crop was planted. The third study evaluated three methods of mechanically killing summer cover crops in North Carolina. Undercutting provided greater than 95% kill for five of six broadleaf species, and two of five grass species. Mowing effectively killed all six broadleaf cover crops, but re-growth occurred with three of five grasses, with the exception of nearly mature German foxtail millet and mature Japanese millet. In general, rolling did not effectively kill broadleaf or grass cover crops, with the exception of nearly mature German foxtail millet, mature Japanese millet and mature buckwheat.