Nutrient management has been one of the most important practices in commercial nursery production of ornamental plants, and N is often considered a limiting factor for plant growth. Plant N status is mainly improved by application of N fertilizer. Increased N during fertilization increased plant biomass and N uptake and improved flower quality of some species, but it also increased nutrient leaching and decreased uptake efficiency (Bi and Scagel, 2008; Bi et al., 2007; Chang et al., 2012). Higher N fertilization rate promoted shoot growth of container-grown Rhododendron L. ‘Karen’ and increased nutrient leaching, whereas decreased N and P promoted root growth and improved nutrient uptake efficiency (Ristvey et al., 2007). Intermediate N rates of 105 and 158 mg·L−1 resulted in greater dry weight, leaf area, and flower number of Anthurium andraeanum Lind. than low N (79 mg·L−1) or high N (210 mg·L−1) rates (Chang et al., 2012). An optimum N rate should be determined based on plant requirements (including species, cultivars, and growth stage) as well as growing conditions such as medium composition, temperature, and moisture (Cardarelli et al., 2010; Gastal and Lemaire, 2002; Gómez-López et al., 2006).
Plant demands for mineral nutrients change in response to different N supply and other growing conditions, which should be considered in fertilization management (Pradubsuk and Davenport, 2010; Strik, 2015). Foliar urea spray in the fall altered plant’s demand of nutrients during winter, when uptake of P, Cu, and Mn increased, whereas K and Mg uptake decreased in Rhododendron ‘Cannon’s Double’ and ‘P.J.M.’ (Scagel et al., 2008a). Leaf concentrations of N, K, Ca, Mg, Mn, sulfur (S), aluminum (Al), and B in bell pepper (Capsicum annum L.) increased with increasing shade level (Díaz-Pérez, 2013). Uptake of different nutrient elements interact with each other. Excessive N (210 mg·L−1) decreased K and Mg uptake and resulted in poor growth of Anthurium andraeanum (Chang et al., 2012). When plants received no N from fertigation, there were deficiencies of P, K, S, and Mn for Rhododendron ‘P.J.M’ and deficiencies of P, K, S, Ca, and Mg for Rhododendron ‘Cannon’s Double’ (Scagel et al., 2008b). With a sufficient N supply, plant growth may be limited by other mineral nutrients; therefore, balanced fertilization programs are necessary to optimize plant growth (Marschner, 2012; Scagel et al., 2012).
Nutrient availability declines with low soil water content, which becomes a limiting factor for nutrients to become soluble to the root surface (Marschner, 2012). Increased irrigation frequency with the same total amount of water has been used to reduce nutrient leaching and compensate for possible nutrient deficiency, and it has varying effects on plant growth and nutrient uptake (Fare et al., 1994; Scagel et al., 2011). Neilsen et al. (1995) reported that higher frequency irrigation improved tree growth of ‘Gala’ apple (Malus domestica Borkh.) compared with lower irrigation frequency. Scagel et al. (2012) reported that net uptake of P, B, and Mn decreased in response to more frequent irrigation in container-grown Rhododendron ‘P.J.M Compact’, ‘English Roseum’, and ‘Gibraltar’, but increased Ca uptake of ‘P.J.M Compact’ and ‘English Roseum’. Plant species vary in their growth and nutrient uptake responses to irrigation frequency (Li et al., 2018, 2019).
Biocontainers made from various biodegradable materials have been investigated as sustainable alternatives to conventional plastic containers for various crops and production systems (Beeks and Evans, 2013a, 2013b; Evans and Hensley, 2004; Evans and Karcher, 2004; Kuehny et al., 2011; Li et al., 2015, 2018, 2019; Nambuthiri et al., 2015; White, 2009). They were reported to have varying physical properties, water consumption characteristics, and influences on plant growth. A variety of biocontainers made from peat, manure, coir, straw, and wood fiber have been found to produce plants with quality similar to that of plants grown in traditional plastic containers (Koeser et al., 2013; Kuehny et al., 2011). Decomposition of feather containers provides an additional N source and resulted in greater dry shoot weights of ‘Janie Bright Yellow’ marigold (Tagetes patula L.), ‘Cool Blush’ vinca (Catharanthus roseus L.), and ‘Orbit Cardinal’ geranium (Pelargonium ×hortorum L.H. Bailey) compared to those grown in peat containers (Evans and Hensley, 2004). The effects of specific biocontainers on plant nutrient uptake require investigation. Therefore, the objective of this study was to investigate the influence of N rate, container type, and irrigation frequency on mineral nutrient uptake of Encore® azalea ‘Chiffon’.
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