Corn and soybean production dominate the U.S. Midwest agricultural landscape, which limits crop diversification. Crop diversification, while being challenged by climate and management practices (Mohammed et al., 2020), can increase agricultural productivity and sustainability (Brummer, 1998; Davis et al., 2012; Gaba et al., 2015). Increasing the bioeconomy of the agriculture sector through biofuel production can promote its sustainability (National bioeconomy blueprint, 2012). Oilseed pennycress grown as a winter annual crop for sustainable aviation fuel could fit into temperate climate regions such as the upper Midwest (McGinn et al., 2019). However, adoption of pennycress may be limited due to its poor germination and establishment (Hazebroek & Metzger, 1990; Sedbrook et al., 2014; Mohammed et al., 2020).

Recent studies that continue to demonstrate pennycress seed yields of 2,400 kg ha^—1 (Cubins et al., 2019) and oil content of 270–390 g kg^—1 (McGinn et al., 2019) highlight the suitability for biofuel generation (Moser et al., 2009b; Moser, 2012; Fan et al., 2013; Mousavi-Avval & Shah, 2020). Pennycress offers a suite of ecosystem services by providing food for pollinators (Eberle et al., 2015; Chopra et al., 2020), promoting the diversity of beneficial arthropods (Groeneveld & Klein, 2015; Groeneveld et al., 2015), suppressing weeds (Johnson et al., 2015), and scavenging residual N from the field (Weyers et al., 2019; Moore et al., 2020). Pennycress also has higher biofuel production potential and lower negative environmental impact compared to other existing oil-producing crops (Moser et al., 2009a; Mousavi-Avval & Shah, 2021).

Successful establishment and subsequent survivability are key requirements for crop production, and without achieving these, a crop is very unlikely to be adopted. Pennycress naturally has a higher degree of seed dormancy, though seed treatments with gas (especially GA4 + 7) have been found to be effective in breaking dormancy and increasing germination in seeds with a black seed coat (Metzger, 1983; Saini et al., 1987; Koirala et al., 2022). Koirala et al. (2022) also reported that seed pelleting increased germination in a black-seeded pennycress line under controlled conditions. Similarly, recent efforts in domestication have led to low-fiber golden pennycress lines that exhibit high germination potential in the absence of exogenous treatment (Ott et al., 2021; Koirala et al., 2023). Improved germination under ideal conditions does not always guarantee better establishment in field conditions (Finch-Savage & Bassel, 2016; Reed et al., 2022), but seed pelleting might be effective to improve field establishment of pennycress as has been demonstrated in other crops (Burns et al., 2002; Gesch et al., 2012; Javed & Afzal, 2020).

Improved establishment under broadcast seeding of pennycress in autumn is desired to facilitate easy intercropping and shortening the time between annual crop harvest and pennycress emergence. Being an emerging crop, pennycress lacks optimized crop management practices (Cubins et al., 2019; Zanetti et al., 2019; Verhoff et al., 2022). Previous studies on pennycress have reported using seeding rates ranging from 1.1 to 16.8 kg ha⁻¹ (Cubins et al., 2019), which may have been an artifact of high seed dormancy and poor establishment. Planting depth and method are also reported to influence pennycress establishment. Phippen et al. (2010) reported drill seeding having a better crop stand than broadcast seeding while Moore and Mirsky (2020) did not observe a benefit of drill seeding over broadcast seeding. Similar studies comparing these two establishment methods did not find a significant difference in seed and biomass yield in pennycress (Phippen et al., 2010; Noland et al., 2018; Moore et al., 2020). CoverCress, Inc (2022) recommends farmers use a 5.6 kg ha⁻¹ seeding rate with surface seeding or seeding <0.6 cm below soil surface during early September through mid-October for golden pennycress “CoverCress™” lines. Soil water availability is identified as the most limiting factor for field emergence (Hazebroek & Metzger, 1990), and precipitation of approximately 13 mm within 3 days of planting is stated as adequate to facilitate establishment (CoverCress, Inc, 2022). The integrated use of seed treatment such as fungicide, pelleting, and GA may increase pennycress establishment in autumn and may lead to increased seed yield. The objective of this study was to assess how different seed treatments (including seed pelleting) affect establishment and yield of different pennycress lines in a range of environmental conditions after broadcast seeding. The hypothesis was that treatments would vary in their efficacy of improving establishment, though gains in germination and establishment would be seen for all over the untreated.

Similarities in pennycress seedling establishment occurred across all sites, suggesting that its potential for production exists over a wide area of the upper U.S. Midwest. Establishment was demonstrated over a wide range of soil pH from 5.0 to 7.2 ( Table 3 ) under broadcast seeding conditions, though autumn precipitation played an important role in establishment. The OSU_NWB site experienced heavy rainfall (71 mm) on the 6th day after sowing, which likely washed out or killed any emerged seedlings. With the failure of plant establishment in all seed treatments of both lines at OSU_NWB, forecasted rainfall may be key in ensuring autumn establishment. Industry recommendations are for 13-mm precipitation within 3 days of planting to facilitate establishment (CoverCress, Inc, 2022); the current study suggests between 10 and 60 mm in the 14 days following seeding may be sufficient for the establishment of surface broadcast seeds. Both OSU_South and UW_2 were not harvested due to excessive weed competition, and both sites were planted after a non-grain crop ( Table 2 ). This indicates that annual crop herbicide programs or past management practices may be more conducive to pennycress establishment compared to other cropping systems. The inability to harvest in these two sites due to high competition supported the idea of low water use efficiency and competing ability of pennycress as discussed by Johnson et al. (2015).

There was an overall increase in plant stand count (averaged across all sites counted) in spring compared to autumn stand count across all seed treatments and both varieties ( Table 5 ). This indicated the presence of spring emergence even with the GA seed treatments that were applied to break dormancy and accelerate germination shortly after planting. A similar increase was reported by Wohrley (2022), though Mohammed et al. (2020) reported a reduction in stand count in spring compared to autumn. All pelleted treatments with or without GA improved number of established plants in spring for black-seeded MN106NS. This increase supported the idea presented by Koirala et al. (2023) of improved seed vigor with these treatments in MN106NS. Conversely, pelleted seed treatments on golden-seeded tt8-t/ARV1 had a negative impact in plant stand count. These results were supported by Koirala et al. (2023) that showed that seed pelleting of golden-seeded decreased seed vigor.

The positive correlation observed between number of plants and green canopy cover ( Table 6 ) was similar to a study reported by Wohrley (2022). However, a negative relationship between these two variables was observed and discussed in Koirala (2022) and was reported in another study of Wohrley (2022) possibly due to plant thinning along with growth and rosette development. Canopy cover of at least 30% of the soil surface is expected in a cover crop to protect soil from erosion (Allmaras & Dowdy, 1985); the maximum observed spring canopy cover averaged across sites (18.7%) was lower than the desired cover of more than 30% to fully realize erosion prevention benefits. This might be due to the use of broadcast seeding in this study, which was reported to have a poor establishment than drill seeding (Phippen et al., 2010). However, the number of plants m⁻² even with drill seeding in the study by Phippen et al. (2010) was less than what was observed for most treatments in the current study.

Despite the positive correlation observed between spring stand count and canopy cover with seed yield, non-pelleted tt8-t/ARV1 had a similar yield to that of MN106NS. The observed yields were similar and within the range of the studies reported by Cubins et al. (2019) in their review of pennycress agronomics. The same article mentioned that a pennycress seed yield of 1,684 kg ha⁻¹ is required to be an economically viable crop, while Trejo-Pech et al. (2019) estimated that a seed yield of 1,335 kg ha⁻¹ was needed to cover production costs. The seed yields observed in the current study across sites were 25% or more below these desired estimates, indicating that the efforts to improve establishment and yield through seed treatments under broadcast seeding were inadequate. Further advances in both genetics and other management practices (i.e., seeding method and seeding rate) will be needed to ensure critical yield levels are achieved.

The golden-seeded line tt8-t/ARV1 experienced a reduction in establishment and yield following most treatments in this study, suggesting that treatment using these methods was not necessary or was detrimental (e.g., pelleting). Even though seed pelleting with GA improved establishment and yield for MN106NS, there was no clear advantage of pelleting over the GA-only treatment as suggested in literature (Scott, 1989; Gesch et al., 2012; Vinod Kumar et al., 2015; Su et al., 2017; Javed & Afzal, 2020). Pelleting could result in improved flow rate in mechanical planters (Burns et al., 2002), though mechanized planting was not assessed in the current study. The treatments from the current study may be used for MN106NS depending on the availability of seed treatment facility, cost of treatment, and goals for treating the seed.

In conclusion, the seed treatments applied in the current study were not enough to fully address the challenge of establishing pennycress as a viable winter annual cash cover crop in the Midwestern United States with broadcast seeding. Rainfall accumulation of more than 60 mm within 14 days of planting can reduce plant establishment; thus, a weather forecast should be considered when deciding a planting period to avoid heavy rain events. Similarly, as rainfall within 7 days prior to planting improved plant stand, it is recommended to broadcast pennycress after a rainfall during autumn for better establishment. It is not recommended to treat the golden-seeded line with the treatments used in the present study, while the black-seeded line had better establishment and yield from seed treatment with GA and the novel seed treatment—seed pelleting with added GA. Pennycress had lower competing ability with other crops and weeds; therefore, a herbicide program needs to be developed for pennycress especially if it is broadcasted following non-grain crops or fallow conditions.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

NK: study design, treatment implementation, data collection, and drafted original manuscript; DB: study design and edited manuscript draft; RG: data collection and edited manuscript draft; YM: data collection and edited manuscript draft; NH: data collection and edited manuscript draft; AH: data collection and edited manuscript draft; SW: data collection and edited manuscript draft; WP: data collection and edited manuscript draft; PT: data collection and edited manuscript draft; AL: study design, treatment implementation, data collection, drafted original manuscript, and incorporated revisions/corresponding author. All authors contributed to the article and approved the submitted version.