Extracted sweet corn tassels as a renewable alternative to peat in greenhouse substrates☆
Research highlights
▶ Soilless substrates are primarily used in the production of containerized greenhouse and nursery crops. ▶ Sphagnum peat moss is a primary constituent of these substrates and its harvest from endangered ecosystems has become a worldwide concern. ▶ Ethanol-extracted, coarse-ground corn tassels were used as a peat replacement for potting substrates. ▶ This research indicates that extracted ground tassels may be utilized as a suitable replacement for peat in greenhouse substrates for tomatoes.
Introduction
Since the 1960s, container production of horticultural crops has primarily utilized soilless substrates (Nelson, 2003). These substrates include organic materials such as peat moss or tree barks blended with other organic or inorganic components such as vermiculite, perlite and sand (Bilderback et al., 2005). Sphagnum peat moss is considered a premier substrate, due to its desirable physical characteristics (e.g. particle size distribution, total porosity, water holding capacity, and bulk density) and high nutrient exchange capacity (Rodale, 1959, Raviv et al., 1986, Nelson, 2003, Bilderback et al., 2005). Increasing public concern around the world has developed over the use of peat, primarily due to ecological concerns over wetland destruction during its harvest (Barkham, 1993, Robertson, 1993; Zeller, 2007; Blok and Verhagen, 2009, Jayasinghe et al., 2010). The utilization of farm, industrial and consumer waste by-products as components of nursery substrates has been extensively investigated during the past several decades (Chong, 2005). Alternatives to peat such as various composts, coir [coconut (Cocos nucifera L.) husk fiber], kenaf (Hibiscus cannabinum L.) stem core, poultry feathers, rice (Oryza sativa L.) hulls, cotton (Gossypium hirsutum L.) gin trash, switchgrass (Panicum virgatum L.), and ground pine (Pinus taeda L.) logs have been examined (Wang, 1994, Pill et al., 1995a, Pill et al., 1995b, Evans et al., 1996, Webber et al., 1999, Noguera et al., 2003, Evans, 2004, Sánchez-Monedero et al., 2004, Papafotiou et al., 2004, Evans and Gachukia, 2007, Papafotiou et al., 2007, Zaller, 2007, Bustamante et al., 2008, Altland and Krause, 2009: Jackson and Wright, 2009, Šrámek and Dubský, 2009, Jayasinghe et al., 2010). Tomatoes are the leading greenhouse vegetable crop grown in the United States (Jones, 2008). While most commercial greenhouse tomato production involves plants grown under one of three soilless hydroponic production techniques (flood-and-drain, nutrient film, or drip irrigation using rock wool or perlite), small greenhouse operations and homeowners primarily utilize several organic soilless substrates, with 50% peat/50% vermiculite (v/v) formulations being the most commonly used (Rippy et al., 2004, Jones, 2008).
Our research team is currently examining the bulk extraction of valuable phytochemicals from sweet corn tassels. The extraction process utilizes 95% ethanol which in addition to extracting these phytochemicals, also removes other constituents such as lipids and soluble proteins which would contribute to off-odors during decomposition of the tassels. The ethanol extraction process also serves to effectively disinfect the tassels. The objective of the present study was to investigate the use of ethanol-extracted, coarsely ground corn tassels as a replacement for peat in soilless potting substrates.
Section snippets
Materials
Corn tassels (Zea mays L. ‘Silver Queen’) were harvested between July 31 and August 7, 2009 in Green Valley, Illinois, and were immediately batch extracted for 24 h with 95% ethanol. Tassels were dried in an oven at 40 °C for 48 h to remove solvent, then ground in a Fritsch Rotor-Speed Mill Model VDE 0520 (Fritsch GmbH, Idar-Oberstein, Germany) fitted with a 4-mm screen. Sunshine® vermiculite (medium particle size) was obtained from Sun Gro Horticulture Distribution Inc., Bellevue, WA. Ferti·lome®
Chemical and physical characteristics of the substrates
The bulk densities of the substrate components used in this study are shown in Table 1. Ground tassel had a significantly lower bulk density (0.097 g cm−3) than either peat moss or vermiculite. While the bulk densities of compost and bark are normally much higher (generally ranging from a low of ∼0.15 g cm−3 for some tree barks up to 0.70 for some composts), it was higher than several types of coir dust (0.04–0.08 g cm−3; Evans et al., 1996), coarsely ground kenaf stems (0.0814 g cm−3; Webber et al.,
Conclusions
Tomato growth and yields in substrates containing tassel were similar to a standard vermiculite/peat substrate, with only the substrate containing 50% tassel being significantly lower for these parameters. Physical and chemical properties were also similar among all the substrates. Although lower container capacities would indicate that more frequent irrigations would be needed as compared to standard greenhouse media, the values with tassel replacing peat moss were similar to the 50% peat
Acknowledgements
The authors gratefully acknowledge the technical assistance of Ray Holloway and Ashley Cranford.
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