Northern highbush blueberries are long-lived perennial plants, requiring 7 years or more to reach full production. The cash costs to establish new plantings, through Year 6, can surpass $30,165/ha with net cumulative returns of –$9,995/ha (a loss) for conventional blueberry in Oregon (Julian et al., 2011a). In contrast, the cash costs required to establish a “typical” organic blueberry field in Oregon were higher ($32,520/ha) but cumulative returns through Year 6 were positive ($6,930/ha; Julian et al., 2011b). In plantings yielding 18 t·ha−1, the breakeven price (to cover total cash costs) was estimated at $3.08 and $10/kg for organic blueberries produced in Oregon (Julian et al., 2011b) and southern California (Takele et al., 2008), respectively. Net cash costs of production are greatly impacted by production system, yield, and price obtained for fruit. Organic production systems for blueberry vary among growers and regions. Although estimated net returns are greater for organic production than conventional (Julian et al., 2011a, 2011b), little is known about the impact of various production systems on the performance and returns of organically grown northern highbush blueberry.
Blueberry plants have shallow roots and grow best on well-drained, high organic matter, acid soils (Eck, 1988). Planting on raised beds is a common production system in blueberry fields (Strik, 2007) to improve drainage and help protect plants from standing water (Scherm and Krewer, 2008). In contrast, planting on flat ground is thought to increase soil moisture and reduce soil temperature during the fruiting season, which is beneficial to root growth of southern highbush blueberry (hybrids of V. corymbosum L. and V. darrowi Camp.; Spiers, 1995) and may be easier to manage for weed control.
In general, the best growth and yield of blueberry have been achieved with N fertilization rates of 25 to 100 kg·ha−1 (Bañados et al., 2012; Chandler and Mason, 1942; Eck, 1988; Griggs and Rollins, 1947; Hanson, 2006; Hart et al., 2006) at an estimated cost of $1 to $2/kg for synthetic N fertilizer. Organic blueberry farmers commonly use Organic Materials Review Institute (OMRI)-approved fish emulsion as a direct liquid application or injected through the drip irrigation system and granular feather meal as N fertilizer sources. Supplying N from feather meal or fish fertilizers has an estimated product cost to growers of $10 to $25/kg N applied.
Application of surface mulch has been shown to improve production in blueberry through improved weed control, soil moisture, and plant growth (Burkhard et al., 2009; Clark, 1991; Clark and Moore, 1991; Krewer et al., 2009; Lareau, 1989; Moore, 1979; White, 2006). Historically, Douglas fir (Pseudotsuga menziesii M.) sawdust was readily available and commonly used in conventional and organic blueberry production systems in the northwestern United States. However, sawdust has become increasingly expensive and has a high carbon (C) to N ratio making plant fertility more difficult and expensive to manage with organic fertilizer products (White, 2006). The use of compost as a mulch in blueberry may have advantages over sawdust. Compost has a lower C to N ratio and releases 3% to 10% of its total N during decomposition for several years after application (Gale et al., 2006; Sikora and Szmidt, 2001).
Weed mat or landscape fabric, an inert mulch (Granatstein and Mullinix, 2008) approved for use as a weed barrier by the USDA Organic National Program (USDA-AMS-NOP, 2011), is an alternative to sawdust mulch. Weed mat is used widely in tree fruit orchards, mainly because of its effectiveness for weed control, although weeds appear in the planting hole and removal by hand may be required (Runham et al., 2000). Sciarappa et al. (2008) reported almost complete control of weeds when using weed mat plus a mulch of coffee grinds around the planting area in organic blueberry in New Jersey. However, concerns have been expressed about possible negative impacts of increasing soil temperature under weed mat on plant growth (Neilsen et al., 2003; Williamson et al., 2006).
Weed management in blueberry is critical for economic production because weed presence decreases yield (Burkhard et al., 2009; Krewer et al., 2009; Pritts and Hancock, 1992; Strik et al., 1993). Pre-emergent and contact herbicides are commonly used in conventional production systems, whereas chemical options are limited to OMRI-approved products containing acetic acid or lemon grass oil in organic systems. Acetic acid (vinegar) at a concentration of 9% to 20% has been effective at controlling some weeds (Fausey, 2003; Young, 2004). Organic growers also use mulch and hand removal to control weeds. Propane flaming may be an option to control smaller weeds but may damage the crop plant (Granatstein and Mullinix, 2008).
The objectives of this study were to evaluate the effects of flat and raised planting beds, three different mulch types, including sawdust, compost plus sawdust, and weed mat, and the use of feather meal and fish emulsion fertilizer applied at two rates on initial establishment costs and returns for organic production of ‘Duke’ and ‘Liberty’ blueberry. ‘Duke’ is an early-season cultivar that ripens in late June to early July in Oregon, whereas ‘Liberty’ is a mid- to late-season cultivar that ripens in late July to early August.
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