Extracted sweet corn tassels as a renewable alternative to peat in greenhouse substrates

Abstract

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 (Zea mays L. ‘Silver Queen’) tassels were used as a peat replacement for potting substrates. Replacing peat moss with increasing levels of ground tassel (up to 50%, v/v) elevated pH and electrical conductance, while having variable effects on substrate physical properties (bulk density, percent solids, air porosity, container capacity, and total porosity). Two identical greenhouse experiments separated by time were conducted using tomato (Solanum lycopersicum L. ‘Red Robin’) plants grown in 6.0-L pots. In the first experiment, all substrates were similar for total tomato yield per plant and number of fruit per plant, with only the 50% tassel substrate having significantly lower values. There were no differences for plant height or average fruit weight among substrates. No differences were found for any of these variables in the second experiment. 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.