Trials Evaluating Solarization and Tarping for Improved Stale Seedbed Preparation in the Northeast USA

Abstract

Stale seedbeds are commonly used by organic vegetable farmers to reduce in-season weed density. The primary purpose of this study was to evaluate the efficacy of soil solarization (clear plastic) with subsequent flaming for stale seedbed preparation. A secondary objective was to compare the efficacy of solarization with tarping (black plastic). Solarization is an established weed management practice in warmer climates, but its efficacy in the humid continental Northeast USA was unknown. We hypothesized that solarization during May-June in Maine, USA would increase weed emergence, and could thereby contribute to depletion of the germinable weed seedbank and, with subsequent flaming, creation of an improved stale seedbed. We expected that firming soil with a roller prior to solarization would further increase weed emergence. Across four site-years of replicated field experiments and two on-farm trials we found that, contrary to expectations, 2 weeks of solarization reduced apparent weed emergence (density) in comparison to nonsolarized controls by 83% during treatment, and 78% after 2 weeks of observation following plastic removal and flaming. Rolling did not significantly affect weed density. Soil temperatures were elevated in solarized plots, reaching a maximum of 47 • C at 5 cm soil depth, compared to 38 • C in controls. Weed community analyses suggested that solarization might act as an ecological filter limiting some species. Addressing our secondary objective, two replicated field experiments compared the efficacy of solarization with tarping applied for periods of 2, 4, and 6 weeks beginning in July. Across treatment durations, solarization was more effective than tarping in one site-year, but tarping outperformed solarization in the other; this discrepancy may be explained by differences in weed species and soil temperatures between experiments. Overall, solarization and tarping are promising stale seedbed preparation methods for humid continental climates, but more work is needed to compare their relative efficacy.

A Review of Non-Chemical Management of Couch Grass (Elymus repens)

“…Afterwards, the area is rototilled and planted with a winter grain or a green manure crop [143]. Birthisel and Gallandt [144] found that solarization in Maine (cloudy climate) did reduce E. repens shoot density, at least in the short term. Unfortunately, the authors did not verify the vitality of the rhizomes exposed to solarization.…”

Tarping Cover Crops Facilitates Organic No-till Cabbage Production and Suppresses Weeds

“…We applied tarps immediately after a precipitation event, but the lack of precipitation in May likely led to a soil water deficit that a single precipitation event was unable to overcome. The efficacy of tarping for weed control relies on adequate soil moisture, which may induce fatal germination of weed seeds (Birthisel and Gallandt, 2019). In dry years, irrigation before tarping may be necessary to make this system most effective.…”

“…The effects of tarping on weed community composition and diversity indicate that tarping, like tillage, can act as a strong filter on weed community assembly (Birthisel and Gallandt, 2019). Variability in how different weed species respond to levels and quality of cover crop mulch (Pittman et al, 2020;Teasdale and Mohler, 2000) show that cover crop mulch itself has a filtering effect on weed community assembly.…”

“…Reusable plastic tarps are increasingly common for small-scale organic farmers who want to manage weeds and facilitate reduced-tillage vegetable production. The use of tarps has been popularized by farming and market gardening books (Fortier and Bilodeau, 2014;Mays, 2020;Mefferd, 2019); however, it has received little attention from researchers (Birthisel and Gallandt, 2019;Lounsbury et al, 2020;Rylander et al, 2020). Many of the farmers featured in these publications apply large amounts of compost (e.g., resulting in mulch depths of 3-10 cm) to bury weed seeds and then deploy tarps between cash crop growing periods to manage weeds and crop residue.…”

Review: How will climate change impact the ‘many little hammers’ of ecological weed management?

“…Solarisation is an intensive form of stale seedbed preparation that utilises clear plastic to trap solar energy, heating soils to temperatures hot enough to kill weed seeds or seedlings (Horowitz et al, 1983;Standifer et al, 1984). We recently demonstrated that solarisation can result in mortality of weed seeds and reduced weed density (Birthisel and Gallandt, 2019) in the Northeast United States, suggesting that its applicability in temperate regions may be greater than previously assumed (Walters and Pinkerton, 2012). Efficacy of this practice generally increases with both ambient air temperature and soil moisture (Mahrer and Shilo, 2012), though it is also strongly affected by light intensity, which is impacted by cloudiness.…”