Pollinator habitat installations can augment nutritional and habitat resources available for pollinators, thereby addressing native pollinator and honeybee declines and corresponding declines in pollination ecosystem services (Vaughan and Skinner, 2008, 2015). These habitats are often comprised of a combination of forbs that bloom throughout early, mid, and late growing seasons, and may contain grasses to provide cover and nesting habitat for vertebrates (FSA, 2013). Pollinator habitat installation is encouraged by federal programs that provide technical and financial assistance to interested farmers. For example, the Natural Resources Conservation Service (NRCS) and the Farm Service Agency (FSA) work with farmers through the Environmental Quality Incentives Program (EQIP) and Conservation Reserve Program (CRP), respectively, to convert arable or environmentally sensitive land to vegetation that provides high-quality habitat and nutritional resources for native pollinators (Vaughan and Skinner, 2008, 2015).
Limiting weed competition is arguably the most important step to ensuring pollinator habitat establishment (Aldrich, 2002; Howell and Kline, 1992; Norcini and Aldrich, 2004; Perry, 2005), and adequate pollinator habitat seedbed preparation can be critical for ensuring sustained weed management throughout the pollinator establishment phase (Aldrich, 2002; Bartels, 1992; Martin, 1986; Wilson, 1992). Pollinator habitat installation guide recommendations for seedbed preparation methods vary (NRCS, 2007, 2012; Vaughan et al., 2013, 2014), but can generally be grouped into soil disturbance (in which topsoil is cultivated) or nondisturbance (no-till with herbicide application, solarization, burns, and/or grazing) practices (Aldrich, 2002).
A review of seedbed preparation studies for wildflower meadow establishment concluded that tilling multiple times, herbicide applications, or both generally provide better perennial weed management than solarization, burning, or grazing (Aldrich, 2002). Comparisons of tillage and herbicide seedbed preparations have generated mixed results. One study demonstrated that tillage yielded better wildflower establishment than herbicides after two years (Ahern et al., 1992), whereas other studies have indicated that both methods resulted in good weed control the first year of establishment (Corley, 1991; Corley et al., 1993). These contrasting results may depend on the specific wildflower species included in mixes as there can be species-specific responses to planting depth, soil bulk density, and critical weed-free periods (Hyder et al., 1955; Knezevic et al., 2002; Monsen and Stevens, 2004). In Virginia, NRCS agents do not recommend tillage because it is purported to stimulate weed growth (B. Glennon, personal communication), but this may be affected by site-specific weed seed bank communities (Chauhan et al., 2006; Oegema and Fletcher, 1972; Yenish et al., 1996).
To inform pollinator habitat establishment, we examined the effects of seedbed preparation in an experiment repeated over 2 years and in observational on-farm trials. This research is unique in that previous studies did not follow USDA seed mix recommendations specific to pollinator habitat establishment programs and were largely conducted on roadside embankments rather than farmland. Furthermore, this work is timely because the current body of peer-reviewed research literature relating wildflower pollinator habitat establishment to seedbed preparation techniques is limited. We followed USDA NRCS recommendations for a pollinator habitat seed mixture appropriate for Virginia (B. Glennon, personal communication) that consisted of nine species of forbs and two species of grasses. The experiments tested the impacts of no-till-plus-herbicide or conventional tillage seedbed preparation on wildflower establishment and weeds. We hypothesized that the establishment of smaller seeded species would be more negatively impacted by preparing the seedbed by tillage than larger seeded species, because of burial too deep for germination. In addition to the repeated experiment, we also tracked seedbed preparation and pollinator habitat establishment on seven farms on the Eastern Shore of Virginia and Maryland. Farmers individually chose how to prepare their pollinator habitat seedbeds with the input of NRCS technical advice; farm-specific constraints such a weed pressures and whether the farm was managed organically influenced the final plan for seedbed preparation.
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Comparison of methods among “Kentland#1” and “Kentland#2” experiments.
Eastern Shore 2016 site locations, sizes, pre-plant treatment, packing regimes, and planting dates.
Pollinator refuge seed mixes by study.