Optimizing Weed Suppression and Nutrient Use Efficiency in Cover Crop-Based No-Till Organic Corn

Many organic grain producers seek weed management tactics that will allow them to reduce tillage in their cropping systems while maintaining weed control and efficient nutrient delivery. In this webinar, Hanna Poffenbarger of the University of Maryland and Steven Mirsky of the USDA-ARS Sustainable Agriculture Systems Lab discuss optimizing cover crop mixture composition and manure application to achieve weed suppression and adequate, efficient nitrogen delivery in a cover crop-based no-till corn system.

Watch the webinar now (recorded March 18, 2013).

Webinar At-a-Glance

Prepared by Kristen Devlin

No-till grain production is the go-to soil conservation practice for improving soil quality and reducing erosion, and it’s no wonder, says Steven Mirsky, a research ecologist with the USDA Agricultural Research Service. During a Cover Crop Innovations webinar, Mirsky explained that no-till grain production saves labor, money, time, and fuel costs. But, it has largely been facilitated by the use of herbicides and the development of herbicide-resistant cash crops, and these tools aren’t available to organic growers.

But organically grown grain is in high demand, with organic feed-corn shortages reported throughout the U.S. Mirsky and his co-presenter Hanna Poffenbarger, a graduate student at the University of Maryland, discussed one possible barrier to increasing organic grain production: Many growers that might consider transitioning to organic are soil-conservation oriented, and are reluctant to implement the intensive tillage that organic weed management often requires.

“If we can develop reduced-tillage or no-till practices in organic systems, this may be the best way to increase the amount of organic production and alleviate some of these shortages,” said Mirsky. “We’ve been looking a lot at organic cover-crop based rotational no-till systems.”

In this type of system, growers optimize cover crop performance by doing the bulk of their tilling before cover crop establishment. This reduces the need for seedbed preparation and cultivation tillage, enabling growers to cut the frequency of their tillage in half.

Much of Mirsky’s focus has been two such systems: cereal rye preceding soybeans,  and hairy vetch preceding corn. The rye-soybean system has been quite successful, with several research sites consistently achieving above-average yields. The success of this system is due largely to the nitrogen-fixing capabilities of soybeans and to the weed-suppressing power of cereal rye. “Rye has been selected because it’s a very persistent residue,” Mirsky explained. “It’s good at suppressing weeds, it’s very winter hardy, you can kill it a lot earlier than most of the cereals, and it provides excellent weed-suppressive mulch.”

The vetch-corn system is not enjoying the same success. Two challenges — inadequate nitrogen (N) and vetch’s inconsistent weed-control efficacy — prompted Poffenbarger’s experiments with cover crop mixtures before corn. Her goals were to increase cover crop biomass in order to maximize weed suppression, and to bring more N into the system at the time when it’s most needed.

Poffenbarger shared results from her studies in which cover crops of pure rye, pure hairy vetch, and a 50/50 mix of the two were planted before corn and measured in terms of their weed-suppression and nutrient-delivery efficacy. In general, adding rye along with vetch increased the biomass of the cover crop, increased the persistence of the mulch, and increased the weed-control efficacy, especially later in the season. But, while the rye was clearly superior at weed suppression, it released no N. The pure hairy vetch plots, on the other hand, released the most N.

This dilemma — inadequate weed control with pure vetch, and inadequate N with pure rye — could be addressed by using a mixture of the two, but there would still be N deficits. Poffenbarger explained, “If we added more nitrogen to our mixture, we could probably get even higher yields and closer to the yield potential of pure vetch.”

This spurred her interest in using manures, but Poffenberger and her colleagues are concerned with synchronizing N supply with demand. Knowing that applying manure before the corn needs it can lead to N losses, they’ve been focusing on side-dress applications, rather than pre-plant applications, to avoid such losses.  Poffenbarger discussed manure application rates, and shared information on integrating manure in a hairy vetch rotation, so as to maximize N while avoiding over-application of phosphorus.

Want more information? See the related SARE grant(s) GNE11-025, Cover crop selection and manure placement for weed suppression and nitrogen use efficiency in a no-till organic corn system.

About this Series

This webinar is part of the Cover Crop Innovations Webinar Series, hosted by Penn State Extension in winter 2013. Other webinars in the series can be found here.

The Cover Crop Innovations Webinar Series is a component of the training initiative sponsored by the Northeast SARE Pennsylvania State Program. More information about the training initiative is available here.