Azaleas are among the most popular ornamental crops in the United States. The market for azaleas in the United States was $18.9 and $18.3 million in 2014 and 2015, with ≈4.1 and 3.69 million plants being sold in these 2 years, respectively (U.S. Department of Agriculture-National Agricultural Statistics Service, 2016). Azaleas are popular for their colorful blooms and various blossom forms. Encore® azaleas are a patented brand series of azaleas that bloom in spring, summer, and fall (Wilson Bros. Gardens, 2018). Multiple blooming seasons require continuous plant growth and nutrient supply. Plant nutrient uptake is subject to a number of factors such as growth rate, climate, and cultivating conditions (Bi et al., 2007b; Gastal and Lemaire, 2002; Million et al., 2007; Scagel et al., 2007). Nutrient uptake varies among crops, between growing seasons, and between production sites (Chang et al., 2012; Pradubsuk and Davenport, 2010; Ristvey et al., 2007; Scagel et al., 2007). The nutrient requirement of a given species or cultivar also fluctuates within a growing season (Strik and Bryla, 2015), which is difficult to predict and has rarely been reported.
The optimal fertilization program relies on specific information regarding the nutrient requirements of a species or cultivar, plant growth stage, climatic conditions, and substrate composition (Cardarelli et al., 2010; Gómez-López et al., 2006; Mengel and Kirkby, 2001). Chang et al. (2012) reported N supply and climate fluctuations interacted to influence the growth and yield of Anthurium andraeanum Lind. They reported N supply to be the limiting factor during spring and summer, whereas climate conditions was the limiting factor during fall and winter in Taiwan, a subtropical climate (Chang et al., 2012). With sufficient N supply, the increase of N content in a plant was believed to be determined by the growth rate of plants rather than by different species or climatic conditions (Gastal and Lemaire, 2002).
Biodegradable containers, also referred as biocontainers, have been investigated in recent years as sustainable alternatives to conventional plastic containers (Hall et al., 2010; Nambuthiri et al., 2015; White, 2009). A variety of biocontainers made from materials such as peat, manure, coir, straw, and wood fiber have been evaluated and found to produce plants of comparable quality to traditional plastic containers (Koeser et al., 2013a; Kuehny et al., 2011). Depending on the hydrophilic or hydrophobic materials that constitute the biocontainers, plants grown in biocontainers have various water-use characteristics, with some of them requiring more water or more frequent irrigation than plastic containers (Evans and Karcher, 2004; Evans et al., 2010; Koeser et al., 2013b). Water availability between irrigation events may then influence nutrient availability to the plant in the substrate (Scagel et al., 2011). The porous nature of the sidewalls of some biocontainers has resulted in greater water use, but increased evaporation was believed to help reduce substrate temperature, which is a beneficial feature at locations where summer heat stress may be a problem for plant growth or survival (Nambuthiri et al., 2015; Wang et al., 2015).
We found in our previous study that the paper biocontainer increased the PGI, root length and surface area, dry weight, and plant N uptake in Encore® azalea ‘Chiffon’ with N rates of 15 and 20 mm compared with traditional plastic containers (Li et al., 2018). However, seasonal growth and the nutrient uptake pattern of azalea plants grown in biocontainers vs. plastic containers remain unknown. Therefore, the objectives of this study were 1) to investigate the plant growth and N uptake pattern of Encore® azalea ‘Chiffon’ during a growing season, 2) to compare plant growth and N uptake of plants grown in conventional plastic containers with those grown in paper biocontainers, and 3) to identify the timing when difference in growth and N uptake may occur.
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