The production of highbush blueberry (Vaccinium corymbosum L.) has been increasing rapidly in the United States from 22,932 to 37,816 ha from 2005 to 2012 (U.S. Highbush Blueberry Council, unpublished data), whereas certified organic production has increased from 194 ha in 2003 (Strik and Yarborough, 2005) and 790 ha in 2008 (USDA, 2010) to an estimated 1665 ha in 2011 (Strik, unpublished data). There has been relatively little research on whether a sustainable and profitable organic production system can be developed for northern highbush blueberry.
Highbush blueberry requires well-drained soil and is often planted on raised beds (Strik, 2007). Raised beds help prevent saturated soils, reduce compaction, improve internal drainage (Magdoff and Van Es, 2000), and reduce disease problems such as Phytophthora root rot (Bryla and Linderman, 2007). Planting on flat ground, on the other hand, is thought to increase soil moisture and reduce soil temperature during the fruiting season, which is beneficial to root growth in southern highbush blueberry (complex hybrids based largely on V. corymbosum and V. darrowi Camp.) (Spiers, 1995).
Weed management is also critical for economic production in blueberry (Pritts and Hancock, 1992; Strik et al., 1993). Pre-emergent and contact herbicides are commonly used in conventional production systems, but chemical options are limited in organic systems. Acetic acid (vinegar) at a concentration of 9% to 20% has been effective at controlling some weeds organically (Fausey, 2003; Young, 2004). Propane flaming is used to control smaller weeds but may damage the plants, especially during establishment (Granatstein and Mullinix, 2008). Organic mulches are commonly used in blueberry to help control weeds (Burkhard et al., 2009; Krewer et al., 2009; Sciarappa et al., 2008), improve blueberry plant growth and yield (Clark and Moore, 1991; Goulart et al., 1997; Karp et al., 2006; Kozinski, 2006; Krewer et al., 2009; Savage, 1942; White, 2006), root distribution through the soil profile (Spiers, 2000), and whip and shoot production (Kozinski, 2006; White, 2006). Douglas-fir (Pseudotsuga menziesii M.) sawdust is a common mulch used in blueberry production in the northwestern United States, but it is expensive (Julian et al., 2011a) and the high initial carbon (C) to N ratio immobilizes N applied from fertilizers (White, 2006). It is often more difficult and more expensive to compensate for N immobilization with organic fertilizer products.
Weed mat (perforated landscape fabric) is considered an inert mulch (Granatstein and Mullinix, 2008) and is approved for use as a weed barrier by the USDA National Organic Program (USDA-AMS-NOP, 2011). Weed mat has been widely used in orchards as a result of its effectiveness for weed control, although weeds can grow in the area cut for the planting hole, and removal by hand may be required in commercial crops (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 production in New Jersey. However, soil temperature may increase under the weed mat and thereby reduce plant growth (Neilsen et al., 2003; Williamson et al., 2006). Magee and Spiers (1995) found that white-on-black polyethylene-based mulches produced greater plant growth and yield than black plastic or black woven fabric mulches in southern highbush cultivars as a result of decreased soil temperature under the more reflective mulches. In Georgia, rabbiteye blueberry (V. virgatum Ait.) established with organic mulches had similar yields to those with weed mat in the first 2 years of establishment but greater yield in Years 3 to 5 (Krewer et al., 2009).
Compost may provide many benefits to blueberry production. As compost decomposes, it releases ≈3% to 10% of total N as mineral N for several years after the initial application (Gale et al., 2006; Sikora and Szmidt, 2001). Burkhard et al. (2009) found greater growth and yield of highbush blueberry when using seafood compost and manure–sawdust compost. Municipal yard debris compost is readily available in many production regions and may be suitable for commercial blueberry production (Costello, 2011).
Highbush blueberry requires N fertilizer at a rate of ≈25 to 100 kg·ha−1 N per year for optimum growth and production (Bañados et al., 2012; Chandler and Mason, 1942; Eck, 1988; Griggs and Rollins, 1947; Hanson, 2006; Hart et al., 2006). Uptake of N fertilizer is most rapid from bloom to harvest (Bañados, 2006; Throop and Hanson, 1997) but continues through the remainder of the growing season (Bañados, 2006). In ‘Bluecrop’, fertilizing with ammonium sulfate (50 kg·ha−1 N) produced more growth and fruit production during the first 2 years after planting than unfertilized plants or rates of 100 or 150 kg·ha−1 N (Bañados et al., 2012). Nitrogen fertilization with different rates of ammonium sulfate also affected biomass accumulation and allocation (Bañados et al., 2012); however, the impact of organic fertilizers on blueberry growth and allocation has not been reported.
Organic blueberry farmers commonly use fertilizer products approved by the Organic Materials Review Institute, including fish emulsion or feather meal as sources of N. Fish emulsion is applied as a direct liquid application to the soil of the in-row area or is injected through the drip irrigation system. Feather meal, a granular product, has a very rapid N mineralization rate, converting 30% to 60% of its total N to mineral N in 14 d in moist soil with cumulative mineral N release of 65% to 75% of total N after 70 d (Gale et al., 2006). Fish fertilizer products also mineralize N rapidly after application to soil. Sullivan et al. (2010) reported equivalent N mineralization rates (58% to 64% of total N converted to mineral N in 28 d) for a variety of fish and feather meal fertilizers.
The objective of the present study was to evaluate the effects of using flat or raised planting beds, three different mulch types, and feather meal or fish emulsion fertilizer on plant growth and early production in a new organic planting of northern highbush blueberry.
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