Soilless mixes that include components of peat, perlite, vermiculite, and other organic materials are commonly used in the greenhouse industry (Barrett et al., 2016; Vaughn et al., 2011). The most common organic component of soilless mixes is peat because of its high water-holding capacity, high porosity, low bulk density, high nutrient exchange capacity, and relatively widespread availability (Barrett et al., 2016; Vaughn et al., 2011). Peat may be composed of many different plant materials, and it is formed through partial decomposition of these plant materials under waterlogged conditions in wetland environments. These peat-forming wetlands comprise a small portion of the Earth’s land surface, ≈3%, but contain an estimated 450 billion Mg of C (Alvarez et al., 2017).
The wetlands that form peat are at significant risk for degradation through harvesting peat (Alvarez et al., 2017), mineralization of peat after draining (Alvarez et al., 2017), fluctuating water levels (Juckers and Watmough, 2014), and plant community shifts due to fluctuations in climate (Schwarzer et al., 2013). Alternatives to peat use are being explored to address concerns regarding reduced long-term sustainability associated with peat harvesting. Potential alternatives include coconut (Cocos nucifera L.) fibers (coir), composts, rice (Oryza sativa L.) hulls, wood chips, biochar, and others (Abad et al., 2002; Alvarez et al., 2017; Buck and Evans, 2010; Barrett et al., 2016; Margenot et al., 2018; Massa et al., 2018; Suo et al., 2013; Xiong et al., 2017). For example, Buck and Evans (2010) and Sambo et al. (2008) found that rice hulls have properties similar to those of peat. Xiong et al. (2017) found that coir, compared to peat, may produce plants of similar size and quality. Furthermore, Abad et al. (2002) found that coir had properties similar to those of peat. Others have found that, based on plant growth or mix properties, biochar from various sources may be suitable as peat alternatives (Alvarez et al., 2017; Margenot et al., 2018; Peterson and Jackson, 2014). Although the effects of such alternatives on plant growth and mix properties vary, the logistics and consistency of products limit their adoption.
One potential organic material that requires further investigation as a peat alternative is processed corn stover (PCS). Corn stover, which is produced at a rate of 185 to 370 Mg annually, is the most abundant and readily available residue in the United States (USDA-NASS, 2017). A fraction (30% to 50%) of the residue produced could be sustainably removed for expanded uses (Blanco-Canqui and Lal, 2009; Graham et al., 2007; Zhao et al., 2015). This means ≈92.5 to 185 Mg can be available for alternative uses. Processed corn stover could have potential as a peat alternative because it may have properties (i.e., pH, nutrient content, and bulk density) similar to those of peat (Pellet Technology USA, Gretna, NE). Research information comparing the use of PCS with peat is, however, limited.
The few previous studies that have evaluated PCS or other crop residues suggested that they may produce biomass yields similar to those of peat (Peterson and Jackson, 2014; Vaughn et al., 2011, 2013). For example, Vaughn et al. (2011) found that using extracted corn tassels at rates of up to 50% produced tomato yields similar to those of peat but, as tassel rates increased, the bulk density of the mix decreased and the pH and EC increased. Similarly, Peterson and Jackson (2014) suggested that wheat straw (Triticum aestivum L.) and corn stover biochars produced through gasification could be considered for greenhouse mixes. None of these previous studies assessed ground corn stover or composted stover as alternatives to peat. Therefore, our objectives were to determine how PCS affects the growth and quality of tomatoes and marigolds and to compare the hydraulic and chemical properties of PCS with those of peat.
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