by Mary Parr and Julie Grossman

The growth in organic agriculture coupled with an emphasis on soil conservation has resulted in increased interest in the roller-crimper implement as a cover crop management tool.  The roller-crimper allows farmers to plant a fall legume cover crop, roll-kill the cover crop just before planting, and plant corn directly into the cover crop mat.  The roll-killed cover crop acts as a mulch for the corn plants, suppressing weeds as well as contributing nitrogen to the crop.

Legume cover crops can accumulate as much as 200 lb N per acre, with the average N content in North Carolina near100 lb N per acre.  Nitrogen content varies by species with hairy vetch having the highest N content – between 150 and 200 lb N per acre.  Crimson clover and Austrian winter pea have about 100 to 150 lb N per acre

It is best to choose annual cover crops that are well adapted to your climate and soil type and produce high amounts of biomass. If early flowering varieties are available, they allow for earlier roll-crimping and planting.  Late flowering cover crops such as sweet clover should be avoided as they do not reach flowering until mid June.

Spring planting in a roller-crimper system is nearly always later than a traditional tilled cover crops system.  The roller-crimper works by damaging the stems of the cover crop during early seed filling stages when energy reserves are low, causing it to die.   If roll-kill is attempted too early, the cover crop will be able to recover.  In North Carolina, the earliest that most cover crops are susceptible to a roller-crimper is in mid to late April, and even as late as May for some varieties, particularly in years with a cool spring.

Because the cover crop residues sit on the surface of the soil, decomposition is more gradual than when tilled into the soil.  It is important to choose a cover crop that will not have lignified stems preventing N from being released.  In trials examining cover crops for the roller crimper, we found that hairy vetch and Austrian winter pea, especially when mixed with rye, were more compatible crops than crimson clover, giving better weed suppression and resulted in higher corn yields.

Things to consider

• Plant your cover crop early enough in the fall to achieve optimal stand and biomass accumulation, preferably before November for legumes.

• The roller crimper only works when the cover crop is in full bloom or early pod set.  If attempted too early, the cover crop will not be killed, and will compete with the corn crop for water and nutrients

• With low cover crop biomass, the roll-crimped cover crop provides little N and no weed suppression.