Worldwide production of highbush blueberry (Vaccinium sp.) has increased tremendously in recent years, from ≈42,000 ha in 2005 to over 109,000 ha in 2014 (Brazelton, 2016). This rapid growth is driven by strong consumer demand for the fruit and recent development of new cultivars and production systems that have increased availability of fresh blueberries in the market year-round.
Highbush blueberry is a member of the Ericaceae family and has unique characteristics relative to other crop plants, including a very fine root system with no root hairs, low soil pH requirements (4.5–5.5), and a preference for ammonium-N (NH4-N) over nitrate-N (NO3-N) (Retamales and Hancock, 2012). Compared with many non-ericaceous crops, blueberry plants contain much lower concentrations of most macronutrients and, therefore, tend to have lower nutrient requirements than other fruit crops (Korcak, 1988), including apple (Malus domestica Mill.; Righetti et al., 1998), raspberry (Rubus idaeus L.; Hart et al., 2006b), and blackberry (Rubus sp.) (Hart et al., 2006a). Because of these unusual requirements, many producers are looking for novel ways to grow the plants in regions with suboptimal soil conditions. One such method involves cultivation in containers with soilless substrate and highly controlled fertigation management systems (Voogt et al., 2014). Although nurseries have been growing blueberry in soilless substrate for many years, the concept of commercial fruit production in containers is a relatively novel idea (Fulcher et al., 2015). Substrate mixes used in nurseries frequently contain peatmoss, coir, bark, and/or perlite, but it is unclear whether these components are also suitable for longer term fruit production of blueberry.
Partially decomposed peatmoss, derived from sphagnum peat, has historically been used for production of container-grown plants. High water holding capacity, high ion exchange capacity, resistance to decomposition, and relative abundance of peat bogs in the northern hemisphere often makes peatmoss an ideal choice for use in soilless substrates (Hammond, 1975). Peatmoss is also naturally low in pH (3.5–4.5) and, therefore, often considered a good substrate for acid-loving plants such as highbush blueberry (Knight et al., 1998; Scagel, 2003).
Coir is the pithy and fibrous material from the husk of coconuts and is a common alternative to peat because of its high water-holding capacity and widespread geographic availability (Evans et al., 1996). Although coir has a higher pH (5.6–6.9; Evans et al., 1996) than peat, it has been shown to be suitable for container production of ericaceous plants. Scagel (2003) reported improved growth in a wide range of ericaceous species when the plants were grown in media with coir instead of peat; however, the media never contained >20% peat or coir by volume. Berruti and Scariot (2011) substituted a peat-based medium with up to 50% coir and found improved growth of several Rhododendron sp. in the mixes with coir.
Growers also often use inexpensive, locally available organic products such as milled tree bark as a substrate for containers. In the northwestern United States, douglas fir bark is widely available as a by-product from the logging industry and is commonly used for production of nursery plants in the region (Buamscha et al., 2007). Douglas fir bark varies widely in quality and properties, depending on how it is treated (fresh, aged, or composted), but it usually has a low pH (3.7–4.4) considered appropriate for blueberry (Altland and Buamscha, 2008).
The purpose of the present study was to investigate the suitability of different combinations of sphagnum moss, coconut coir, and douglas fir bark for container production of highbush blueberry. These ingredients were chosen because of their low cost and widespread use in soilless cultivation. We hypothesized that blueberry would grow best in substrates with a high proportion of peat or douglas fir bark because of the lower pH. To test the hypothesis, southern highbush blueberry (a complex hybrid based largely on Vaccinium corymbosum L. and Vaccinium darrowii Camp.) plants were grown in media mixes with different proportions of the substrates.
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