Utilizing cover crops is a common practice for many vegetable producers, due to the numerous benefits of reducing soil erosion, scavenging nutrients, suppressing weeds and improving soil structure and organic matter.
Planting no-till into killed cover crops has additional benefits of leaving residues that suppress weeds on the soil surface, reducing the number of trips through the field and further reducing soil erosion.
Most no-till cropping systems rely primarily on herbicides to kill cover crops, leaving organic growers and those wishing to reduce synthetic pesticide inputs with fewer tools to successfully implement no-till systems.
Cover crop roller-crimpers were developed to mechanically kill or suppress cover crops. They have several advantages over mowing, in that fewer trips are required to suppress the cover crop, less energy is used, residues persist longer and the residue is neatly laid in one direction, facilitating planting.
Despite the benefits of rolled and crimped cover crops and no-till systems, some crop residues may not adequately suppress weeds, may be difficult to plant into and can delay crop emergence.
In addition, if weeds are not adequately suppressed by the cover crop residues, these systems limit growers' options to remove weeds by cultivation. There may also be impacts on diseases, insects, slugs and other pests that have not been fully studied.
Killing or suppressing cereals and legume cover crops with roller-crimpers has been tested by USDA's Agricultural Research Service (ARS) in Auburn, Miss., for about a decade, and more recently by Rodale Institute, various universities and other ARS sites.
Studies have shown that cover crops of cereal rye and hairy vetch must be rolled and crimped at an advanced stage of growth in order to adequately suppress or kill the cover crop. If rolled and crimped at earlier stages of growth, cover crops are often able to recover and can compete with the main crop as a weed.
Due to the requirement to roll and crimp at such a late stage of growth, late-planted vegetable crops such as pumpkins, squash, beans and transplanted peppers or tomatoes are better suited to no-till vegetable production systems that utilize roller-crimpers.
Studies were conducted in 2009 and 2010 by ARS researchers Rick Boydston in Washington and Marty Williams in Illinois to evaluate no-till snap bean production systems utilizing fall-planted cover crops of cereal rye, common vetch or hairy vetch.
The research tested rolling and crimping either once or twice at rye anthesis or later. Other treatments included herbicides applied after rolling and crimping once. The roller-crimper used in these studies was a 10-foot-long, 18-inch-diameter steel cylinder with 3-inch fins protruding from the cylinder in a chevron pattern, and was filled with water to add weight.
Cover crops were rolled when cereal rye had reached 95 percent anthesis, common vetch was fully flowered with small flat pods (Washington) and hairy vetch was beginning to flower (Illinois).
Rolling and crimping killed cereal rye from 90 percent to 98 percent, and rolling a second time wasn't beneficial. Cereal rye produced 3.6 to 5.4 ton/acre dry residue, and reduced final weed dry weight in the snap bean crop by about 75 percent compared to control plots without any cover crop.
In Illinois, in year one of the study, snap bean stands were poor when following cereal rye, primarily due to poor planter performance when the planter unit lined up directly over rows of cereal rye. In year two, bean stands were improved by killing cereal rye in mid-April with glyphosate applied in a narrow band over the intended snap bean row.
In Washington, cover crops were rolled and crimped and snap beans were planted in a perpendicular direction to cover crop planting, and bean stands were comparable to no cover crop controls. Although cereal rye residues greatly suppressed weeds, snap bean yields following rye were reduced in Illinois in both years, but were similar to the yield of control plots with no cover crop in Washington.
Common vetch produced 1.7 to 2.9 ton/acre dry matter in Washington, and hairy vetch produced 1.8 to 2 ton/acre dry matter in Illinois. Common vetch and hairy vetch cover crops were not completely killed by rolling and crimping at either location. A second rolling and crimping did not significantly improve vetch kill.
Snap bean stands were lower in Washington following common vetch, primarily due to failure of press wheels on the no-till planter to completely close the seed furrow when planting into rolled and crimped vetch residues.
PROS AND CONS. Cover crop roller-crimpers have several advantages over mowing, in that fewer trips are required to suppress the cover crop, less energy is used, residues persist longer and the residue is neatly laid in one direction, facilitating planting. (USDA photo)In Illinois, snap bean stands following vetch were comparable to control plots without a cover crop. Snap bean bloom was delayed following vetch compared to no cover crop controls, partly due to competition from non-killed vetch.
In general, weeds were suppressed by vetch residues, but less than with cereal rye residues. The final dry weight of non-killed vetch was equal or greater than the weight of weeds at snap bean harvest in three of four site-years.
Snap bean yields following vetch were generally lower than control plots with no cover crop, due to a combination of reduced stands and suppressed growth due to competition from weeds and non-killed vetch.
Cereal rye and vetch mixtures were also tested at both locations and produced similar biomass to that of cereal rye alone.
It was noted that cover crop residues persisted until the time of snap bean harvest, which could impede machine harvest of snap beans. Growers contemplating using no-till vegetable production systems must weigh the potential benefits of these systems with the inherent risks.
Implementing vegetable no-till systems that utilize rolled and crimped cover crops will require use of no-till planting equipment that can operate in heavy crop residues.
Producers attempting to implement these types of systems should start on a small scale and have a backup plan in situations where cover crops are not completely killed or where weeds are not adequately suppressed by cover crop residues.