Submitted to: Weed Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/5/2012
Publication Date: 3/1/2013
Citation: Mirsky, S.B., Ryan, M.R., Teasdale, J.R., Reberg-Horton, C.R., Curran, W.S., Spargo, J.T., Wells, S.M., Keene, C.K., Moyer, J.W. 2013. Overcoming weed management challenges in cover crop-based organic rotational no-till soybean production in the Eastern US. Weed Technology. 27(1):193-203. Interpretive Summary: No-till management is widely recognized as the optimal strategy for conserving soil resources. However, this practice has been largely successful due to inexpensive, effective herbicides and genetically modified cash crops such as roundup ready soybean. There is a need to develop grain production systems that utilize no-till management for soil conservation but lower the selective pressure of herbicides and risks of weed resistance. Cover crop-based, organic rotational no-till is one potential solution to this challenge. Reducing tillage in organic grain production can reduce production costs and labor in addition to conserving soil resources. However, without tillage or chemical options, weed management requires a cover crop-based approach. In cover crop-based, organic rotational no-till, fall planted cover crops are flattened into a weed suppressive mulch in the spring and a cash crop is no-till planted into the mulch. Soybean no-till planted into cereal rye has been the most consistent cover crop/cash crop combination thus far. This is because rye produces excellent weed suppressive mulch. The weed suppressive mulch must reach high levels (>8000 kg ha-1) in order to provide season long weed suppression. Planting rye early, delaying termination, increasing seeding rate, and ensuring adequate fertility are all strategies for achieving these high levels of cover crop biomass. That said, high weed seedbank densities and perennial weeds could limit the success of this system. Therefore, high residue cultivation can serve as a supplementary control tactic. Other cultural strategies used to increase the competitiveness of soybean includes higher seeding rates and narrower row spacing. Reducing tillage in organic systems has great promise for improving the sustainability of organic grain production, but will require a systems approach to managing crop, soil, and weeds to improve the consistency in yield performance. This research will serve as a framework to growers for reducing tillage in organic soybean production.
Technical Abstract: Cover crop-based, organic rotational no-till soybean production has been gaining traction in the Eastern region of the United States because of the ability of this new system to enhance soil conservation, reduce labor requirements, and decrease diesel fuel use compared to traditional organic production. This system is based on the use of cereal rye cover crops that are mechanically terminated with a roller-crimper to create in-situ mulch that suppresses weeds while soybean are growing. In this paper, we report on a series of experiments that were conducted over the past decade in the Eastern region on cover crop-based, organic rotational no-till soybean production, and we outline current management strategies and future research needs. Much of our research has focused on maximizing cereal rye growth and performance because of the crucial role this cover crop plays in weed suppression. Soil fertility and cereal rye sowing and termination timing affect biomass production and these factors can be manipulated to achieve levels greater than 8,000 kg ha-1, which has been identified as a threshold for consistent suppression of annual weeds. Manipulating cereal rye seeding rate and seeding method (e.g. drill vs. broadcast) also influences ground cover and weed suppression. In general, weed suppression is species-specific, with early emerging summer annual weeds (e.g. common ragweed), high weed seed bank densities (e.g. > 10,000 seeds m-2), and perennial weeds (e.g. yellow nutsedge) posing the greatest challenges. Recognizing these challenges and that optimal cover crop performance is not always possible, we have also tested the effects of high-residue inter-row cultivation, which is an effective supplemental weed control tactic. In addition to cover crop and weed management, we have made progress with planting equipment and planting density for establishing soybean in thick residue. Our current and future research will focus on integrated multi-tactic weed management, cultivar selection, insect pest suppression, and nitrogen dynamics as part of a systems approach to advancing this new production system.