Farmers commonly use intensive tillage in U.S. vegetable production to prepare seedbeds, incorporate crop residue, and remove weeds. Intensive tillage, however, decreases long-term soil health, causing compaction, loss of structure, and loss of organic matter. Reducing tillage over time leads to improved soil aggregate stability, water retention, and infiltration (Arshad et al., 1999; Mendoza et al., 2008; Power et al., 1986). Reduced-till soils also have increased organic matter, nutrient retention, and biological activity compared with tilled soils (Beare et al., 1997; Franzluebbers, 2002; Gupta and Germida, 1988; Hungria et al., 2009; Tebrügge and Düring, 1999).
Despite these benefits, reduced-till in organic systems often results in lower crop yields compared with organic conventional-till systems (Halde et al., 2015; Leavitt et al., 2011), and weed management is a primary challenge constraining reduced-till adoption by organic farmers (Lowry and Brainard, 2017). Weed density and biomass are commonly higher in reduced-till systems than in conventional-till systems (Campiglia et al., 2018; Cavalaris and Gemtos, 2002; Nakamoto et al., 2006). Although conventional farmers may increase use of herbicides when reducing tillage (Buhler et al., 1994), organic farmers primarily rely on cultivation and need more alternatives for improving weed management.
Reduced-till systems can be particularly challenging for direct-seeded root crops, such as beets (Beta vulgaris L.), for which farmers often rely on a fine, residue-free seedbed for planting. Beets are also poor competitors with weeds when they first emerge, and early-season weed control is crucial for a successful crop. Sugar beet yield is often decreased in reduced-till compared with conventional-till systems (Cavalaris and Gemtos, 2002; Koch et al., 2009); however, others have documented that yields can be similar between the two tillage approaches (Van den Putte et al., 2010). To our knowledge, no studies have evaluated organic table beet performance in reduced-till systems.
The application of temporary, impermeable, black plastic tarps to the soil surface before cash crop planting is an alternative weed management strategy recently popularized (Fortier, 2014), and adopted by some organic vegetable farmers (Rylander and Raucher, 2019). Tarps are durable, opaque, 0.15-mm (5- to 6-mil) polyethylene plastic applied to multiple crop rows at a time. Farmers can apply and remove tarps multiple times in a season and use them for several years. This practice is in contrast to well-studied black plastic mulch films (Abu-Gharbieh et al., 1988), which remain in place during crop growth, and to solarization with temporary placement of transparent plastic sheets on the soil at times of intense sunlight and warm temperatures. Solarization can reduce weed pressure and increase yields in numerous crops (Candido et al., 2011; Egley, 1983; Kanaan et al., 2018; Khan et al., 2012; Linke, 1994; Samtani et al., 2017); to be effective, soil temperatures must reach 40 to 65 °C to kill weeds, weed seeds, and other pests (Abu-Gharbieh et al., 1988; Egley, 1983; Öz, 2018).
Tarps may reduce reliance on tillage by providing a number of similar services. Tarps applied for 3 weeks suppress weeds before crop planting and create a weed-free seedbed in which to plant (Birthisel, 2018; Lounsbury et al., 2018; Rylander et al., 2020). Tarps also have the potential to promote fatal germination of some weeds by blocking light from emerged seedlings, but this may depend on other management factors, including the duration and timing of tarp use and soil disturbance before tarp application. The effect of tarps on weed seeds is also likely species specific. Although tarps have shown no effect on Chenopodium album L. seed germination and degradation, survival of Amaranthus powellii S. Wats. seeds in the top 1 cm of soil can be higher under tarped compared with untarped soil, indicating a lower germination and degradation rate under tarps (Rylander et al., 2020).
Earlier results from this experiment, presented in Rylander et al. (2020), found tarping can create a soil environment favorable for crop planting by increasing soil moisture, temperature, and soil nitrate, while decreasing weeds by 95% to 100% at planting time without soil disturbance. Three weeks of tarp duration was adequate to achieve differences compared with untarped controls. The following research investigated the effect of black plastic tarp durations on weeds and yields of a direct-seeded beet crop and compared three levels of tillage intensity after tarp removal. We hypothesized that 1) tarping would lower weed density and biomass during beet crop growth, 2) tarping would increase beet crop yield, 3) differences in tarped and untarped soils would be greatest within no-till systems, and 4) longer tarp durations would have a greater effect on these responses.
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