Organic vegetable farmers rely on intensive tillage to control weeds, incorporate amendments and residues, and prepare seedbeds. Intensive tillage, however, can lead to a decrease in long-term soil health. Placing opaque plastic tarps on the soil surface weeks or months before planting can reduce weed pressure and may facilitate organic reduced tillage strategies, but few studies have documented tarp effects on crop productivity. The effect of tarp duration and tillage intensity on weeds and beet crop yields (cultivar Boro) was evaluated at three locations (Freeville, NY; Riverhead, NY; and Monmouth, ME), for two planting dates and over 2 years (2017 and 2018), resulting in a total of 10 experiments. Tarps were applied for three durations before projected planting dates: 1) 10+ weeks (long), 2) 6 to 8 weeks (mid), and 3) 3 to 5 weeks (short), then compared with an untarped control (none). Three levels of tillage intensity were applied after tarp removal: 1) 10 to 20 cm (conventional till), 2) 3 to 8 cm (reduced till), and 3) left undisturbed (no till), to understand interactions between tillage intensity and tarping. Tarp use of three or more weeks lowered weed biomass for several weeks after beet planting and at-harvest across most locations and years, but tarp duration beyond 3 weeks did not result in further reductions. Tarp use lowered at-harvest weed biomass and increased crop yield for reduced- and no-till systems with results similar to conventional-till. Tarping for 3 weeks could improve the viability of reduced- and no-till approaches for organic vegetable production.
Intensive tillage degrades soil structure, decreases soil organic matter, and can cause soil compaction and erosion over time. Organic vegetable farmers are often dependent on tillage to incorporate crop residue, control weeds, and prepare seedbeds. Black, impermeable, polyethylene tarps applied on the soil surface and removed at planting can help suppress weeds before planting and reduce farmers’ reliance on tillage. However, little is known about how black tarps affect planting conditions and how they can be used to advance reduced tillage production systems. This study investigated the effects of tarp use and tarp duration on the soil environment, surface cover crop residue, and weed suppression to assess the efficacy of using tarps to improve reduced- and no-till practices for organic vegetable production. Experiments were conducted at three sites in the northeastern United States (Freeville, NY; Riverhead, NY; and Monmouth, ME) for 2 years. Following the termination of an oat cover crop, tarps were applied over untilled soils and left in place for four time periods: untarped (control), 3 to 5 weeks (short), 6 to 8 weeks (mid), and 10 or more weeks (long) before two removal dates. Soil moisture and temperature, cover crop residue, soil inorganic nitrogen, weed seed survival, and weed percent cover were measured after tarp removal. Soil moisture and temperature were generally higher under tarps at the time of removal compared with untarped areas at 10% to 55% and 1 to 3 °C, respectively, but the effects were inconsistent. Tarps significantly increased soil nitrate concentrations by 2-times to 21-times with longer tarp durations, resulting in higher concentrations compared with untarped controls. Tarps did not affect the amount of soil covered by cover crop residue and had no consistent effects on weed seed survival of Amaranthus powellii S. Wats. or Chenopodium album L., two common annual weed species in the Northeast. Tarping for at least 3 weeks reduced the weed percent cover by 95% to 100% at the time of removal. Increasing tarp duration beyond 3 weeks did not affect any measures except soil nitrate concentrations. These results indicate that tarps can facilitate the use of reduced-till and no-till practices for organic vegetables by creating a nutrient-rich and moist soil environment free of emerged weeds before planting without soil disturbance.