“If you roll it too early, it’s very difficult to kill. The root system is strong and it will compete with the cash crop for moisture and nutrients, and that can reduce the yield,” Kornecki says.

Conventional growers can use herbicides to kill their cover crops, but organic growers don’t have that option. They are at the mercy of their planting schedules and must sometimes roll cover crops before they are at the right stage for termination.

Assessing impacts on sweet corn

Several different crimpers have been developed, but none has been evaluated for no-till conventional and organic vegetable operations. To get some answers, Kornecki and his colleagues assessed the effects of three experimental roller-crimper systems on soil moisture, yield, and rye termination rates over three growing seasons in a northern Alabama sweet corn field.

Each year, they planted the rye in October and crimped it the following April. They planted sweet corn 3 weeks after crimping the rye — seeding it directly into the rye residue with a no-till planter — and harvested it in August.

They passed the crimpers over the rye at two different speeds (3.2 and 6.4 kilometers per hour) to assess the effects of speed on rye termination rates and soil moisture.

The rollers evaluated were an original straight bar, similar to technology developed in South America; a smooth roller with a crimping bar; and a two-stage roller that has both a smooth drum and a spring-loaded crimping bar.

The latter two rollers were designed and patented by Kornecki. They compared the rollers to a control treatment where glyphosate was applied to kill the rye and a smooth drum roller was used to flatten it.

They found that roller type and operating speed did not affect soil moisture. At either speed, the rollers produced higher yields than the control treatment in the first year of the study, when rainfall was plentiful, and in the second year, when drought occurred.

None of the roller designs was as effective at killing the rye as the glyphosate control treatment, however, with overall termination rates of about 50 percent, well below the recommended 90 percent.

But that was because the researchers did what most growers do: They planted the cash crop at the recommended planting dates, which meant rolling the rye earlier in its growth cycle than when it ideally should have been rolled. The researchers believe that with improved timing, the rollers could produce optimal termination rates.

The results, published in 2012 in HortScience, give guidance to organic vegetable growers who cannot use herbicides. The researchers recommend that growers in Alabama minimize the risk of low termination rates by planting rye by late September instead of mid-October so that it can be rolled 2 weeks earlier in the spring. They also recommend making multiple passes with the roller to increase termination rates.

Kornecki is seeking commercial partners to develop the two larger, patented rollers evaluated in the study as well as a new one he has developed and patented. Intended for smaller operations, it can be guided like a lawn mower and uses a 2-wheel walk-behind small tractor as a power source.

This research is part of Agricultural System Competitiveness and Sustainability, an ARS national program (#216) described at www.nps.ars.usda.gov.

"Rolling Out Cover Crops for Higher Yields and Improved Soil Quality" was published in the February 2013 issue of Agricultural Research magazine.