The widespread use and disposal of petroleum-based plastic containers in the green industry has generated serious concerns (Evans and Hensley, 2004; Hall et al., 2009; Levitan and Barros, 2003). Biocontainers are containers made of biodegradable or compostable materials from plant and animal waste to degradable by-products from various industries (Hall et al., 2010; Nambuthiri et al., 2015a; White, 2009). A variety of biocontainers, such as peat, manure, paper, and straw, have been studied in recent years as potential alternatives to traditional plastic containers.
Biocontainers may increase, decrease, or have no effect on plant growth, depending on plant species or container type (Beeks and Evans, 2013a; Evans and Hensley, 2004; Koeser et al., 2013b; Kuehny et al., 2011). ‘Score Red’ geranium (Pelargonium ×hortorum) and ‘Grape Cooler’ vinca (Catharanthus roseus) had greater shoot growth when they were grown in 5-inch plastic containers than being grown in bioplastic or rice straw containers (Kuehny et al., 2011). ‘Rainier Purple’ cyclamen (Cyclamen persicum) plants had higher dry root weights when grown in paper and wood fiber containers than those grown in plastic containers (Beeks and Evans, 2013a). For some plant species, for example ‘Dazzler Lilac Splash’ impatiens (Impatiens wallerana), its root or shoot growth was similar among all tested container types [plastic, paper, rice hull, peat, coconut fiber, composted dairy manure, Fertil (80% cedar fiber, 20% peat; Fertil International, Boulogne-Billancourt, France), and bioplastic] (Kuehny et al., 2011). Regardless of the difference in growth, Kuehny et al. (2011) found that all the tested containers can produce quality commercial plants of geranium and vinca for retail or landscape uses, consistent with results indicating that ‘Florida Sun Jade’ coleus (Solenostemon scutellarioides) plants grown in biocontainers were of equal size and quality as those grown in plastic containers under a certain irrigation type (Koeser et al., 2013a).
Biocontainers have varying material-derived water consumption characteristics compared with traditional plastic containers due to the distinctive hydrophilic or hydrophobic characteristics of sidewall materials (Evans and Karcher, 2004; Koeser et al., 2013b). By comparing water use of bedding plants like vinca, impatiens, and ‘Yellow Madness’ petunia (Petunia ×hybrida) in various container types (plastic, bioplastic, peat, manure, rice hull, straw, wood fiber, coir, and poultry feather), it was reported that the effect of container type was significant among containers on both water loss per container and total water consumption (Evans et al., 2010; Koeser et al., 2013b). Plants grown in peat and feather containers required more water and more frequent irrigations than those grown in plastic containers (Evans and Karcher, 2004). Similarly, the amount of water used to produce geranium was higher and the average intervals of irrigation were shorter when using peat, Fertil, coconut fiber, composted dairy manure, and rice straw containers than using traditional plastic containers (Evans et al., 2010).
Compared with efforts to evaluate the influence of biocontainers on water use and plant growth of bedding plants in greenhouse production, there has been limited research regarding performance of woody nursery crops in biocontainers and no studies associated with PIP production systems. One of the known advantages of a PIP system in nursery production is that it prevents blow-over of the plants because pots are planted in-ground and protects overwinter plants from cold injury without any overwintering structure requirement. The PIP system was reported to increase root growth and uniformity of root systems for some landscape plants, possibly by lowering substrate temperature during growing season (Ruter, 1993).
Compared with field production, irrigation management is crucial with a PIP production system since plant roots cannot spread outside the socket pot (outside pot to provide sufficient stiffness and strength to prevent the soil from compressing and pinching the two containers together) into the ground to absorb surrounding water. Appropriate irrigation practice in a PIP system was proven to increase irrigation efficiency and longevity of slow-release fertilizer (Ruter, 1998; Zhu et al., 2005). Zhu et al. (2005) applied a new irrigation system (with micro spray stakes, drainage water measurement devices, container-substrate moisture probes, a weather station, and data loggers) in PIP production of Red Sunset maple (Acer rubrum ‘Franksred’), and they found that it not only helped reduce water use but also improved nutrient use efficiency by having closer monitoring over moisture level of the substrate.
A concern with the application of biocontainers in PIP system is root escape from the production pot (the inside pot that hold the plant), especially with plants that have vigorous root growth. Root growing out of the production pot through the drainage hole can cause problems with harvesting when the socket pots are often destroyed. Degradation of the container wall is also impacted by irrigation practices, temperature, container material, etc. (Lopez and Camberato, 2011). Evans et al. (2010) reported that biocontainers made from different materials have varying dry and wet strength. With containers able to absorb water into the container wall, their strength decreased when wet (Evans et al., 2010; Koeser et al., 2013b). In order for biocontainers to be used to produce woody plants that have a longer production period, they have to stay intact long enough through the production cycle without being penetrated by roots and be able to withstand mechanical handling in the subsequent processes of harvesting and shipping (Koeser et al., 2013a). The objectives of this study are to evaluate the mechanical performance of two paper biocontainers in a PIP production system and to investigate how biocontainers affect plant growth and water use of river birch.
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