The greenhouse industry relies on a wide range of containers when producing commodities like flowering potted crops, perennials, annual bedding plants, and vegetable transplants. Petroleum-based plastics (plastic) are the most common materials used in container fabrication. Advantages of using plastic include its durability, resistance to mildew and algae growth, and the ability to mold it into a variety of shapes and sizes. After use, plastic containers used in greenhouse production are typically discarded. As a result, large volumes of plastic waste are stored at greenhouse sites or sent to landfills. Biocontainer use offers one potential solution to this solid waste issue. Biocontainers consist of plant- or animal-byproduct-based containers that break down quickly when planted into the soil or placed into a compost pile.
The greenhouse industry generally categorizes biocontainers as being plantable or compostable (Evans and Hensley, 2004; Evans et al., 2010). Plantable biocontainers are those that allow plant roots to grow through their walls and may be directly planted into the final container, the field, or the planting bed. Compostable biocontainers cannot be planted into the soil because plant roots cannot physically break through container walls, or the biocontainers do not degrade quickly enough to allow plant roots to grow through the container walls. As such, these containers must be removed before planting. If placed in a compost pile, they will decompose in a relatively short time (Mooney, 2009).
There are numerous commercially available plantable biocontainers. Composted dairy manure containers (CowPot Co., Brodheadsville, PA) are made of composted, compressed cow manure held together with a binding agent. Peat containers (Jiffy Products, Kristiansand, Norway) consist of peat and paper fiber. Paper containers (Western Pulp Products, Corvallis, OR and Kord Products, Lugoff, SC) are made from paper pulp with a binder. Rice straw containers (Ivy Acres, Baiting Hollow, NY) are composed of 80% rice straw, 20% coconut fiber, and a proprietary natural adhesive as a binder. Wood fiber containers are composed of 80% cedar fibers and 20% peat and lime (Fertil International, Boulogne Billancourt, France). Coconut fiber containers are made from the medium and long fibers extracted from coconut husks and a binding agent (ITML Horticultural Products, Brantford, ON, Canada).
Compostable biocontainers tend to be more impervious to water than their plantable counterparts. One type of compostable biocontainers available for greenhouse production is a rice hull container made of ground rice hulls with a binding agent (Summit Plastic Co., Tallmadge, OH). Another group of compostable biocontainers are constructed from wheat starch-based bioplastics that are thermoformed into containers (TerraShell, Summit Plastic Co.). Additional containers made from soy-based bioplastics are also under development (Currey et al., 2013).
Categorized as compostable containers above, ricehull and bioplastic containers may be modified so they function as plantable products. Rice hull containers are produced with slots and holes in their sides to allow roots to penetrate into the surrounding soil after installation. Bioplastic sleeves lack a bottom and may have slits in the side walls to serve a similar function. These modifications allow the plant to survive even if the container remains intact for a growing season or more.
One of the major areas of research on biocontainers has been to compare irrigation requirements to those of traditional plastic containers. Evans and Karcher (2004) found that when comparing peat, feather fiber, and plastic containers, the peat containers had the highest rate of water loss through the container walls, and both feather fiber and peat containers required more water and more frequent irrigation when growing a crop than did the traditional plastic containers. When various biocontainers and plastic containers were compared, the crops grown in peat and wood fiber containers had the highest water usage (Evans et al., 2010), but the frequency of irrigation and amount of water used was not significantly different among bioplastic, rice hull, and traditional plastic containers. Beeks and Evans (2013) reported the total irrigation volume required to grow a single ‘Rainier Purple’ cyclamen (Cyclamen persicum) planted in a 6-inch container for 15 weeks ranged from 15.75 L for the plastic container to 24.19 L for a wood fiber container. While the wood fiber containers tested required a greater amount of water than the plastic containers to grow the cyclamen, all other containers evaluated had a similar irrigation demand as the control. Beeks and Evans (2013) also reported that the irrigation interval ranged from 0.6 d for the wood fiber container to 1.3 d for the plastic container. Peat, dairy manure, wood fiber, and rice straw containers had irrigation intervals that were shorter than a plastic control container. The bioplastic, solid ricehull, slotted ricehull, paper, and coconut fiber containers tested had irrigation intervals similar to the plastic control container.
Although research has been conducted on biocontainers to compare water use as compared with plastic controls, all of the studies to date evaluated individual containers placed freely and unprotected on bench surfaces. However, in most cases, particularly with small sizes, containers are usually placed in plastic shuttle trays for ease of handling and spacing. These trays would inevitably affect evaporation from the porous container walls and overall plant water use. Consequently, the objective of this study was to evaluate water use of various biocontainers placed freely on a bench compared with biocontainers placed in plastic shuttle trays. The results of this work can be applied by growers who are concerned both with the water consumed and waste generated as a result of their production efforts.
Beeks, S. & Evans, M.R. 2013 Physical properties of biocontainers used to grow long-term crops in an ebb-and-flood subirrigation system HortScience 48 732 737
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