Diversifying agriculture and finding ways to sustainably feed more people with ever-shrinking farmland has become increasingly important. One option to increase production on limited farm space is to use intercropping systems. Intercropping is the process wherein two or more crops are grown in the same plot to more efficiently use space (Andrews and Kassam, 1976). In addition to not competing for light and space, plants used in an intercropping system must be temporally and physiologically compatible for this growing method to work.
Other options for increasing crop production include using rowcovers and high tunnels for season extension (Lamont, 2009). High tunnels are low-cost structures used for season extension and to protect high-value specialty crops from sudden dips in temperature or damage from high winds and hail (Belasco et al., 2013; Ward and Bomford, 2011). Because high tunnels are heated with passive solar energy, they do not use electricity and are ideal for the cold winters of northern New Mexico, where there is ample sunlight to warm the air in high tunnels even when temperatures fall below freezing (Hecher et al., 2014). In New Mexico, high tunnels can be constructed for as little as $2 to $3 per square foot, making them more economically viable than greenhouses for many small-scale farmers (Walker et al., 2012). Investing in a high tunnel means a farmer may produce crops earlier and can expect to produce longer with the ability to charge premium market prices (Carey et al., 2009). Studies conducted in New Mexico growing blackberry cultivars in high tunnels have shown blackberry to produce 1 to 3 weeks earlier and produce over a longer period than those grown in fields (Yao et al., 2018). In similar high tunnel studies, blackberry yields have more than doubled with the use of high tunnels while reducing pest pressure and lowering the need for pesticide applications (Demchak, 2009; Rom et al., 2010).
Winter greens were chosen for their high market value when grown organically and their suitability to cooler temperatures and frost tolerance (Ernst et al., 2012; Heyduck et al., 2019; Johnny’s Selected Seeds, 2019; Walker et al., 2012). In this study, ‘Red Russian’ kale and ‘Bloomsdale Long Standing’ spinach were selected as the annual winter intercrops. The temperature range for optimal production of kale is between 45 and 60 °F (Johnny’s Selected Seeds, 2019). The temperature range for optimal spinach production is between 60 and 65 °F with lethal minimum temperature being 0 and 5 °F (Walker et al., 2012). Kale grows to a mature leaf size in 50 d, whereas spinach grows mature-sized leaves in 45 d (Walker et al., 2012). Similar maturity rates and harvest methods make the greens compatible for this intercropping study where plots of both greens were often harvested at the same time. These two greens species were also chosen because they could be direct seeded in autumn under the dormant blackberry canes and harvested multiple times in the “cut and come again” method (Voyle, 2014). High tunnel growing also consistently produces high-quality produce because it can prevent crop stress by maintaining a more controlled growing environment (Lamont, 2009). Previous surveys of commercial growers have shown that high tunnels may be beneficial for the production of winter greens worldwide by protecting crops from inclement weather and through season extension (Lamont, 2009). The use of high tunnels in other states with similar climates to that of northern New Mexico have been successful in growing blackberry, kale, and spinach (Borrelli et al., 2013; Lamont, 2009; Lamont et al., 2003; Yao et al., 2018). In addition, kale, spinach, and blackberry are already being grown and sold in local farmers’ markets in northern New Mexico.
In previous studies, growers report that cane fruit grown in high tunnels also produces higher quality fruit with a longer shelf life than field grown berries (Lamont, 2009). Both cultivars of blackberry are floricane-fruiting, meaning that they grow productive floricanes off of 1-year-old primocanes (Galletta et al., 1998a). Blackberry, like other cane fruit, are perennials and require a period of winter dormancy with a gradual increase in temperatures to break dormancy and promote bud formation (Black et al., 2008). The primocanes must maintain good vine health over the winter dormancy to be able to bud out into fruitful floricanes the following spring (Black et al., 2008). Blackberry has a lethal minimum temperature of 0 °F, after which canes will exhibit damage and be less fruitful (Yao, 2018). To be fruitful, blackberry needs a dormancy period with 300 to 900 chilling hours spent in temperatures below 45 °F (Stanton et al., 2007). Blackberry canes can live for 15 years and are productive for 9 years, depending on cultivar and cultivation practices (Takeda et al., 2002). The goal of this study was to determine the functionality of growing winter greens and blackberry in an organic year-round intercropping high tunnel production system. The objective was to evaluate yield and quality of two blackberry cultivars in an organic open field without any intercropping and in a high tunnel intercropped with kale and spinach.
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