Abstract
With organic farming hectarage and cover crop interest increasing throughout the United States, effectively timed cover crop termination practices are needed that can be utilized in organic conservation tillage production systems. Four commercially available termination treatments approved by Organic Materials Review Institute (OMRI) were evaluated, immediately following mechanical termination with a cover crop roller/crimper and compared to a synthetic herbicide termination to access termination rates. Treatments included rolling/crimping followed by (1) 20% vinegar solution (28 L a.i. ha−1 acetic acid), (2) 2.5 L a.i. ha−1 45% cinnamon (Cinnamomum verum L.) oil (cinnamaldehyde, eugenol, eugenol acetate)/45% clove oil (eugenol, acetyl eugenol, caryophyllene) mixture, (3) 0.15 mm clear polyethylene sheeting applied with edges manually tucked into the soil for 28 days over the entire plot area (clear plastic), (4) broadcast flame emitting 1100 °C applied at 1.2 k/h (flame), (5) glyphosate applied at 1.12 kg a.i. ha−1 (this non-OMRI-approved, non-organic conservation tillage cover crop termination standard practice was included to help ascertain desiccation, regrowth, and economics), and (6) a non-treated control. Five cover crop species were evaluated: (1) hairy vetch (Vicia villosa Roth), (2) crimson clover (Trifolium incarnatum L.), (3) cereal rye (Secale cereale L.), (4) Austrian winter pea (Pisum sativum L.), and (5) rape (Brassica napus L.). Three termination timings occurred at four-week intervals beginning mid-March each year. In April or May, organic producers are most likely to be successful using a roller crimper as either a broadcast flamer for terminating all winter covers evaluated, or utilizing clear plastic for hairy vetch, winter peas, and cereal rye. Ineffectiveness and regrowth concerns following cover crop termination in March are substantial. Commercially available vinegar and cinnamon/clove oil solutions provided little predictable termination, and producers attempting to use these OMRI-approved products will likely resort to cover crop incorporation, or mowing, to terminate covers if no other practice is readily available.
Highlights
In 2018, US vegetable farmers produced over 7.53 million hundredweight on over one million hectares, with a value of over US $12.9 billion [1]
Applied at 1.2 k/h, (5) glyphosate applied at 1.12 kg a.i. ha−1, and (6) a non-treated control
As the world’s largest market for organic food, organic vegetable production in the United States comprises 8.4% of total vegetable land area, and sales from organic production are more than US $5.5 million [3]
Summary
In 2018, US vegetable farmers produced over 7.53 million hundredweight (cwt; 100 pounds) on over one million hectares, with a value of over US $12.9 billion [1]. For organic producers and producers considering transitioning to organic production, there are numerous management practices (e.g., reduced tillage, cover cropping, crop rotation, and intercropping) that are beneficial to soil quality [4,5]. Integration of reduced tillage in vegetable production can be challenging due to lack of recommended practices, among others [12]. Weed emergence is reduced while the cover crop is growing, as well as through the release of allelopathic compounds produced after soil incorporation [6,14,16,17,18]. In reduced tillage organic systems, cover crop residue remains on the soil surface after termination to suppress weed growth through both chemical and physical means [9,19,20,21,22]. Common cover crops include fall-planted species such as cereal rye, crimson clover (Trifolium spp.), pea (Pisum spp.), vetch (Vicia spp.), and radish (Raphanus spp.) [6,23]
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