Cover Crop Termination Treatment Impacts Weed Suppression Potential

Abstract

Weed management in tobacco (Nicotiana tabacumL.) is accomplished primarily with soil-residual herbicides, cultivation, and hand removal. Management practices that reduce weed emergence, like reduced tillage and cover crop mulches, may improve weed management efficacy. Depending on cover-cropping goals, growers face trade-offs in species selection and management priorities—producing weed-suppressive mulches may lead to transplanting difficulties and soil-residual herbicide interception. Managing more complex cover crop mixtures may result in different challenges. We established on-farm trials across 4 site-years to study impacts of cover crop composition [wheat (Triticum aestivumL.) monoculture or mixture], termination treatment (early or late chemical termination or removing aboveground biomass), and soil-residual herbicides on weed density and biomass. The cover crop mixture contained cereal rye (Secale cerealeL.), crimson clover (Trifolium incarnatumL.), and hairy vetch (Vicia villosaRoth.), with canola (Brassica napusL.) at 1 site-year. The mixture typically produced more biomass than monoculture wheat, although composition had few impacts on weed density or biomass. With residual herbicides, termination treatment had few impacts on weed density, suggesting that residues did not adversely affect herbicide efficacy. Without residual herbicides, early-season weed density was often higher following the late-terminated cover crop compared with other termination treatments, though midseason weed density was typically lower. When termination treatment affected final weed biomass, it was lower following late termination, with one exception—crop establishment was reduced at 1 site-year, leading to reduced weed–crop competition and greater weed biomass. Our results suggest that growers can use mixtures and, if well-timed to a rainfall event for incorporation, still effectively use soil-residual herbicides to maintain adequate weed control in tobacco regardless of how the cover crop is managed. Later termination, resulting in more residue, may lead to less weed biomass accumulation in the absence of herbicide use.

Impact of Tillage and Crop Residue Management on the Weed Community and Wheat Yield in a Wheat–Maize Double Cropping System

“…Agronomic practices can affect the weed flora and species composition of the weed community and soil seed bank in arable fields [7]. Crop rotation [8,9], fertilization [10][11][12][13], tillage [14][15][16], and crop residue retention [17][18][19] are effective measures to control weeds. No-till has been widely accepted in recent decades for many environmental benefits, such as reducing run-off, improving nutrient cycling, reducing soil degradation, decreasing water and soil pollution, and enhancing the activities of soil biota [20].…”

Cover crops are not affected by tobacco soil residual herbicides but also do not provide consistent weed management benefits

“…Greater amounts of precipitation reduce carryover potential (Tharp and Kells 2000) and resulted in less herbicide retention on surface residues (Ghadiri et al 1984). Moreover, sulfentrazone plus carfentrazone applied over heavy cover crop residues resulted in good weed control when rainfall occurred soon after application, suggesting retention on residues was not occurring (Haramoto and Pearce 2019). In 2016, 346 and 477 mm of precipitation fell between herbicide applications (the POST clomazone and the PREs, respectively) and cover crop planting, whereas 474 and 690 mm of precipitation fell in 2017 during these intervals.…”

“…Though in-season cultivation is more difficult with these management practices, the combination of cover crops with strip tillage may contribute to WM by creating surface mulches that reduce weed emergence and suppress growth (Brainard et al 2013). Our previous research with strip-tilled tobacco has shown that more cover crop residue led to lower weed density but that a soil-residual herbicide was still necessary for adequate weed control (Haramoto and Pearce 2019). Although soil-residual herbicides do not provide adequate full-season control, they may still interfere with successful establishment and growth of subsequently planted cover crops (Cornelius and Bradley 2017;Palhano et al 2018).…”

“…Earlier tobacco harvest dates (i.e., early to mid-September for earlymaturing varieties) allow tobacco growers to also utilize legume cover crops that require earlier planting dates (Clark 2012). Tobacco is typically fertilized with high rates of N fertilizer (Pearce et al 2019), and cover crop mixtures containing legumes did not increase yields beyond a monoculture wheat cover crop (Haramoto and Pearce 2019). However, cover crop mixtures including legumes are promoted by agencies such as the USDA National Resource Conservation Service for their soil-building properties (NRCS n.d.).…”

Zero Soil Treatment Technology As Element Of Economic Efficiency In Cultivation

“…However, studies show that with the use of traditional machines, the entire minimization often comes down to replacing plowing with rootless processing methods, unjustified simplification of technology, or replacing mechanical operations with herbicides. In most cases, the quality of processing remains unsatisfactory and gives a low economic effect (Demir & Gözübüyük, 2019;Haramoto & Pearce, 2019;Obade, 2019). Obviously, a dispute about the advantages and disadvantages of dumping and dumping tillage methods, especially proposals to universalize the use of each of them, which has been going on for the last decades, can only be resolved on the basis of new conceptual approaches to the technology of growing crops using a new-generation agricultural equipment.…”