Blackberries are a very important specialty crop in the United States, especially in Oregon, where they are particularly suited to the climate (Strik and Finn, 2012). In Oregon, 23.9 million kilograms of conventional blackberries were produced on 2954 ha in 2011 (National Agricultural Statistical Service, 2013). In 2008, organic blackberries were harvested on a reported 348 farms in the United States for a crop value of $4.6 million (Geisler, 2012). Given the 12% growth of sales from 2009 to 2010 (Organic Trade Association, 2011) for organic fruits and vegetables, the outlook for organic blackberry production continues to be positive.
Organic production requires the use of various cultural and biological methods for pest management and the use of natural fertilizer sources (animal, plant, or mined origin) for nutrient management [U.S. Department of Agriculture (USDA), 2011]. In organic production, fertigation, the application of fertilizer through a drip irrigation system, has become more common (Fernandez-Salvador, 2014; Harkins et al., 2013; Schwankl and McGourty, 1992). System design and costs (Gaskell and Smith, 2007) need to be considered when adopting irrigation/fertigation systems. Blackberry fields can be successfully established using drip irrigation (Harkins et al., 2013), but fertigation with organic fertilizer sources may lead to plugging of the drip emitters over time (Fernandez-Salvador et al., 2015a). In the present study, organically approved liquid fertilizers that could be fertigated were selected.
Weed management during planting establishment is important for maximizing plant growth and yield (Harkins et al., 2013). The use of woven polyethylene groundcovers (“weed mat”) has been shown to be an effective weed management strategy in plantings of trailing and semierect blackberry plants that do not produce primocanes from root buds (Fernandez-Salvador et al., 2015b; Harkins et al., 2013; Makus, 2011).
Growers who focus on fresh market production systems are interested in growing blackberry cultivars that extend the fruiting season, have a high yield, and produce high-quality fruit. Cultivars must have good postharvest fruit quality and an acceptable shelf life for shipping and for storage, which can range from 14 to 21 d (Fan-Chiang and Wrolstad, 2010; Joo et al., 2011; Perkins-Veazie et al., 1996, 1999, 2000; Perkins-Veazie and Clark, 2002). Unlike in conventional production (Finn et al., 1997, 2005a, 2005b, 2005c, 2011; Strik, 1992; Strik and Finn, 2012), there is relatively little information available on cultivar adaptation to organic production systems (Fernandez-Salvador et al., 2015b; Harkins et al., 2013).
The objectives of our study were to evaluate four fresh market blackberry cultivars (‘Obsidian’, ‘Black Diamond’, ‘Onyx’, ‘Metolius’) and two advanced selections (ORUS 1939-4, ORUS 2635-1) in an organic production system during the establishment years. Genotypes were compared for plant growth and yield and postharvest fruit quality and marketable days at 5 °C. ‘Obsidian’ is a trailing cultivar with vigorous plant growth, very high yield, and large fruit. As a primarily fresh market blackberry, it has excellent flavor and ripens early in the northwestern United States (Finn et al., 2005a; Finn and Strik, 2014). Under conventional management, yield and berry weight for ‘Obsidian’ ranged from 19 to 28 t·ha−1 and 5.5 to 6.8 g, respectively (Finn et al., 2005a). ‘Black Diamond’ is the second most important cultivar grown for processing in Oregon, where its characteristic high yield and thornless canes make it well suited to machine harvesting (Finn et al., 2005a; Finn and Strik, 2014). Yield has been as high as 21 t·ha−1 in conventional production (Finn et al., 2005a) and 13 to 17 t·ha−1 in organic production systems (Fernandez-Salvador et al., 2015b; Harkins et al., 2013). ‘Black Diamond’ may also be hand-harvested for fresh market, because fruit are large, firm, uniformly shaped, and have good flavor (Finn et al., 2005a). ‘Onyx’ is a relatively new cultivar producing vigorous canes and a moderate yield of uniform, firm, sweet, and excellent-flavored fruit suited for local and wholesale fresh markets (Finn et al., 2011). Yield of ‘Onyx’ averaged 14 t·ha−1 in conventional management systems (Finn et al., 2011). ‘Metolius’ is characterized by vigorous plant growth, a good yield, and medium-sized, firm fruit with excellent flavor (Finn et al., 2005b). In conventional production trials, the trailing, thorny ORUS 1939-4 had high yields with medium to large, firm, sweet fruit with excellent flavor. ORUS 2635-1 is a high-yielding selection that produces high-quality, large fruit on a fairly erect, thorny plant (Strik et al., unpublished data).
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