Submitted to: Weed Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/4/2011
Publication Date: 7/1/2011
Citation: Ryan, M.R., Curran, W.S., Grantham, A.M., Hunsberger, L.K., Mirsky, S.B., Mortensen, D.A., Nord, E.A. 2011. Effects of Seeding Rate and Poultry Litter on Weed Suppression From a Rolled Cereal Rye Cover Crop. Weed Science. 59:438-444. Interpretive Summary: High levels of cover crop biomass is critical to the suppression of weeds when used as a mulch. While there have been efforts to document the role of management timing on subsequent biomass of a cereal rye cover crop, often growers are limited by the time in which they can plant their cover crops. Therefore, growers using cover crops for weed suppression need options for enhancing cover crop performance other than altering their management timing. We investigated the role of increasing cereal rye seeding and fertility application rate on cover crop biomass and subsequent weed suppression. Seeding rate did not increase cereal rye biomass; however, increasing fertility rate did result in higher cereal rye biomass levels. On the the other hand, while there were modest increases in cover crop biomass from additions of poultry litter, increasing fertility levels resulted in greater late season weed biomass. Increasing cereal rye seeding rate did not increase cover crop biomass production, but did increase early spring ground cover and resulted in lower late season weed biomass. Early spring ground cover was well correlated with late season weed biomass. Therefore, while increasing cover crop biomass is an important component of suppressing weeds with a surface mulch, increasing soil fertility levels can also enhance weed performance. Finally, increasing early spring ground cover appears to be an important driver in overall weed suppression in a reduced tillage organic cropping system. Future work needs to identify what are the mechanisms by which early spring ground cover in cover crops influence late season weed biomass.
Technical Abstract: Growing enough cover crop biomass to adequately suppress weeds is one of the primary challenges in reduced-tillage systems that rely on mulch-based weed suppression. We investigated two approaches to increasing cereal rye biomass for improved weed suppression: (1) increasing soil fertility and (2) increasing cereal rye seeding rate. We conducted a factorial experiment with three poultry litter application rates (0, 80, 160 kg N ha-1) and three rye seeding rates (90, 150, and 210 kg seed ha-1) in Pennsylvania and Maryland in 2008 and 2009. We quantified rye biomass, immediately after mechanically terminating it with a roller, and weed biomass and density at 10 weeks after termination (WAT). Rye biomass increased with poultry litter applications (675, 768, and 787 g m-2 in the 0, 80 and 160 kg N ha-1 treatments, respectively), but this increase in rye biomass did not result in a decrease in weed biomass. In contrast, increasing rye seeding rate did not increase rye biomass, but did result in a reduction in weed biomass (328, 279, 225 g m-2 in the 90, 150 and 210 kg seed ha-1, treatments respectively). In 2009, we sampled ground cover before rolling and weed biomass and density at 4 WAT. Despite no treatment effects, we found a correlation between the percent of bare soil before rolling and weed biomass at 4 WAT. Our results suggest that increasing rye seeding rate can be effective, and that bare soil in early spring can influence weed biomass both indirectly by affecting weed emergence and density, and directly through other mechanisms such as light quality.