Recent decades have seen tremendous strides in improving the sustainability of greenhouse production (Nelson, 2012). The introduction of closed-loop irrigation, integrated pest management, energy-efficient greenhouse designs, improvements in lighting technology, alternative heating sources, and greenhouse media have all led to improved efficiencies and decreased impacts on the environment (Nelson, 2012). However, more recently, the heavy use of plastic as pots in greenhouse production has come under scrutiny and has been identified as a target for improving sustainability. Alternative containers made from recycled materials, bioplastic, and various organic materials have all been suggested as replacements for the very successful, efficient, easy-to-use, and cheap plastic pot that has been in use in the industry for the last 50 years (Koeser et al., 2014; Nambuthiri et al., 2015). With only a few containers on the market a decade ago, more than 10 alternative containers types are now available for purchase or in the testing phase of development (Evans and Karcher, 2004; Evans et al., 2010; Koeser et al., 2014; Nambuthiri et al., 2015).
Alternative containers differ from petroleum-based plastic pots in that they are made of plant-derived materials and are plantable or compostable. To break down in soil or in a composting environment, alternative containers are essentially designed to degrade over a relatively short period of time. However, a recent study showed that alternative containers that perform well after 1 year of production in a pot-in-pot nursery setting fail American Society for Testing and Materials (ASTM) compostability tests and do not properly degrade during composting tests (Wang, 2013). These same pots failed as container during the second year of the study before the end of the scheduled production period (Li et al., 2015).
While the easy to compost design characteristic may reduce end-of-use landfill waste for some compostable alternative containers used in short-term greenhouse production, both premature failure and limited compostability of new containers may also limit alternative containers compatibility with medium- to long-term or multiseason ornamental nursery crop production systems (Li et al., 2015; Wang, 2013). This potential limitation is reflected in the market. Alternative containers are more readily available in sizes commonly used in commercial greenhouse production (short-term production), while they are much less prevalent in larger sizes most suitable for woody nursery production (long-term production) (Nambuthiri et al., 2015). Additionally, a survey of greenhouse professionals and nursery producers and researchers found that compatibility with existing equipment and production practices was a minor hindrance for greenhouse professionals but a significant obstacle for nursery producers when adopting sustainable production practices like alternative containers (Dennis et al., 2010, Koeser et al., 2013a).
The integrity and longevity of alternative containers are impacted by the specific conditions of the greenhouse. High-input greenhouse production accelerates plant growth and shortens production time. However, the elevated temperature, humidity, and substrate nitrogen levels associated with these controlled environments hasten organic matter degradation as well as plant development. As such, even the comparatively short crop rotations common in greenhouse operations may be too long with respect to container appearance and integrity (Evans and Karcher, 2004; Evans et al., 2010; Kuehny et al., 2011). Given that unsightly or damaged containers may be largely unsellable to the plant-buying public, both of these measures of container performance may ultimately affect the economic sustainability of alternative containers (Hall et al., 2009, 2010).
Past research has investigated alternative containers degradation and strength loss after simulated greenhouse production. However, these assessments are generally limited to short-term crop production and a limited number of alternative containers. In 2004, Evans and Karcher assessed residual pot strength for plastic, peat, and feather pots after a 5-week growing period (Evans and Hensley, 2004; Evans and Karcher, 2004). Evans et al. (2010) later expanded on this work by measuring pot crush and puncture strength for eight commercially available alternative containers after 4 weeks in production. While a longer, 10-week study was conducted by Helgeson et al. (2009), the sole alternative containers tested in the work was a prototype container constructed by hand using a zein-based bioplastic, which is not commercially available to greenhouse producers. In addition to production limitations based on the physical integrity and appearance of alternative containers, questions have been raised and some cases answered about the environmental impact (Koeser et al., 2014), consumer and producer acceptance and adoption (Hall et al., 2009, 2010; Yue et al., 2011), and water use (Evans et al., 2010; Koeser et al., 2013b). These factors together with cost will also undoubtedly have impact on acceptance and adoption of alternative containers.
The study reported herein investigated plant growth, pH and EC, residual container strength, and potential for algal growth for nine alternative containers and a plastic control. In addition to two new container types, bioplastic and bioplastic sleeve, our research expands on the past work of Evans et al. (2010) and Kuehny et al. (2011) by investigating two crop lengths, a short-term (6 weeks) production period and a long-term (12 weeks) production period. In adding the longer production cycle, this work investigates the feasibility of alternative containers use in the production of slower-growing greenhouse plants and limits of alternative containers designed for short-term production. Beyond measures of container performance, this study also investigates impacts on plant growth and quality. The combined results are intended to assist commercial growers interested in adopting alternative containers in their own greenhouse operations.
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