Corn (Zea mays L.) and soybean [Glycine max (L.) Merr] dominate the landscape of the Upper Midwest and demand for alternative land use to increase food and fuel production have increased in recent years (Sindelar et al., 2017). One opportunity created by this demand is the implementation of winter annual crops, such as winter camelina [Camelina sativa (L.) Crantz], to temporally expand the use of land already in production (Martinelli and Galasso, 2011; Gesch and Archer, 2013; Heaton et al., 2013). It is estimated that 27 million ha used for corn and soybean production in the Upper Midwest can be temporally intensified; this land use change can provide additional income to growers as well as ecologic and environmental services to the community at large (Heaton et al., 2013; Johnson et al., 2015; Sindelar et al., 2017). Winter camelina is of particular interest as it has a short growing season, requires low nutrient inputs, tolerant to drought, and can survive the harsh Upper Midwestern winters to produce both food- and industrial- grade oil (Zubr, 1997; Martinelli and Galasso, 2011; Moser, 2012; Zanetti et al., 2013; Allen et al., 2014).
Prior research demonstrated that winter camelina can provide a suite of environmental benefits including nitrogen sequestration, pollinator habitat and forage. For instance, a study by Johnson et al. (2017) demonstrated that winter camelina significantly reduced nitrogen in the soil profile up to 60 cm in comparison to a soybean crop alone. Mitigating nutrient loss from agricultural fields during spring is a key issue in the Upper Midwest (Randall et al., 1997) and the implementation of winter camelina could help to decrease some of the risk associated with fallow land in early spring (Carpenter et al., 1998).
Winter camelina not only provides ecological benefits, but also has the potential to increase farm economic viability as its seed can be used to produce both food- and industrial-grade oil (Zubr, 1997; Moser, 2012; Zanetti et al., 2013; Allen et al., 2014). Alternative biodiesel feedstocks, like winter camelina, have gained interest due to their low costs, compatibility with existing equipment and the ability to integrate them into current agronomic systems (Moser et al., 2009; Sindelar et al., 2017). Moreover, fuel properties of camelina-based biodiesel are similar to those of soybean-based biodiesel, thus indicating its acceptability for use as a biodiesel source (Moser, 2012).
Although camelina has been cultivated since 4000 BCE, recent interest in its oil, particularly omega-3 fatty acids and seed meal, has spurred research in this crop (Zubr, 1997; Berti et al., 2016). Furthermore, recent research (Berti et al., 2017) has indicated that winter camelina can be double- or relay-cropped with forage or food crops leading to improvements in yield per area and energy balance, while also providing several ecosystem services. Although winter camelina shows great promise as a winter annual crop, it still has some issues that need to be addressed. For instance, a study by Sintim et al. (2015) showed that camelina grain yield was reduced by 24% when seed pods were harvested at 90% maturity as opposed to 50% maturity. Seed loss that occurs due to mechanical and environmental disturbances often can be correlated to low plant moisture (Vera et al., 2007; Sintim et al., 2016). This indicates that physiological maturity in camelina occurs prior to full plant ripening and thus, waiting until the plant has fully matured can impact overall yield negatively, likely due to seed shedding and/or avian predation (field observations).
No information exists with respect to (1) the seed moisture content at physiological maturity of winter camelina in the Upper Midwest and (2) changes in seed storage oil and fatty acid composition while maturing in the field under variable environmental conditions. Previous studies have addressed the physiological development of camelina seed but under controlled environment conditions (Pollard et al., 2015) or done elsewhere (Rodríguez-Rodríguez et al., 2013). Therefore, the objectives of this study were to determine (1) the best harvest time to optimize seed yield and quality, (2) the changes in fatty acid composition as seeds grow and mature under field conditions, and (3) seed moisture content at physiological maturity. Determining when physiological maturity occurs in field-grown winter camelina will help target when to apply desiccants to hasten its harvest, thus allowing rapid subsequent planting of the second crop in double-crop systems in the Upper Midwest to improve overall production and economics.
