Floriculture crops had a wholesale value of $4.4 billion in the United States in 2015 (U.S. Department of Agriculture, 2016). The floriculture industry produces many crops using specialized substrates, and many of these crops are produced from seeds. An ideal seed propagation substrate is firm enough to support a seed, allows for gas exchange to ensure oxygen is present for developing roots, holds water to facilitate hydration of the seed without promoting anoxia, is free of pathogens, and is economical (Hartmann et al., 2011). Sphagnum peat, perlite, and vermiculite are commonly used in propagation substrates. Growing concern about the economic and environmental costs of these ingredients has fueled interest in alternative substrate materials (Landis and Morgan, 2009; Owen et al., 2016). One alternative product may be biochar (Altland and Locke, 2012; Dumroese et al., 2011; Northup, 2013).
Biochar is a pyrogenic carbonaceous material (PCM) used to enrich soils (Brown et al., 2015; Lehmann and Joseph, 2015). Terms for PCMs have been a source of confusion. Activated charcoal, biochar, char, and charcoal all have unique definitions, yet these definitions are not used consistently (Brown et al., 2015; Camps-Arbestain et al., 2015; Fitzer et al., 1995). Turning carbon-rich waste products into biochar has the potential to reduce greenhouse gas emissions, recycle agricultural waste, and create a valuable substrate ingredient for plant production systems (Ippolito et al., 2012). Biochar physical and chemical properties vary with source material and production techniques (McLaughlin et al., 2009), so the results of studies using biochar must be interpreted accordingly.
PCM has been advocated and used in horticultural settings in the United States since the early 1900s in nurseries (Retan, 1915) and as a soil amendment or topdressing for turfgrass (Morley, 1927, 1929) in char or charcoal form. Biochar has been studied as a potential substrate component for horticultural production (Dumroese et al., 2011; Santiago and Santiago, 1989). It has been tested as a replacement for vermiculite (Headlee et al., 2014), perlite (Northup, 2013), and peat (Steiner and Harttung, 2014; Vaughn et al., 2013). In container production settings, it can have favorable chemical and physical properties, and plant growth has been unchanged or increased compared with controls (Dumroese et al., 2011; Graber et al., 2010; Headlee et al., 2014; Vaughn et al., 2013).
Most research testing biochar or other forms of PCM in seed propagation or plant establishment substrates has focused on ecological or field agricultural applications, as opposed to soilless substrate culture in containers. Seed germination studies with potato (Solanum tuberosum L.; Bamberg et al., 1986) and sunflower (Helianthus annuus L.; Alburquerque et al., 2014) have shown increased germination rates when activated charcoal was added to the respective substrates. Keeley and Pizzorno (1986) reported increased germination of herbaceous California chaparral plant seeds [Emmenanthe penduliflora Benth. and Eriophyllum confertiflorum (DC.) A. Gray] when exposed to char or heat-treated wood products in screened potting soil. They concluded that the presence of heated xylan and glucuronic acid were involved in promoting germination. Two studies have reported an increase in wheat (Triticum aestivum L.) germination in soils amended with biochar (Solaiman et al., 2012; Van Zwieten et al., 2010). Nair and Carpenter (2016) reported that germination increases in peppers (Capsicum annuum L.) produced in cell trays with soilless mixes amended with hardwood biochar, whereas Liopa-Tsakalidi and Barouchas (2017) reported that pepperoncini (C. annuum L. ‘Stavros’) germination increases in an acidic soil amended with wood chip biochar and no germination change in alkaline soil amended with the same biochar. Also, biochar addition has resulted in no significant changes in maize (Zea mays L.), soybean [Glycine max (L.) Merr.], radish (Raphanus sativus L.), mung bean [Vigna radiata (L.) R. Wilczek], sunflower, or wheat germination (Free et al., 2010; Paneque et al., 2016; Solaiman et al., 2012; Van Zwieten et al., 2010). A reduction in germination percentage after biochar amendment has been reported for mung bean, subterranean clover (Trifolium subterraneum L.), and wheat (Solaiman et al., 2012).
Plant establishment and growth in substrates amended with biochar or other forms of PCM have been variable. Increases in fresh and dry weight, root length, and plant height have been reported, as well as decreases. The rate of biochar inclusion, base substrate or soil, biochar volatile matter, biochar-free radicals, synergistic effect with fertilizers, and crop selection have all been identified as factors (Deenik et al., 2010; Liao et al., 2014; Solaiman et al., 2012; Van Zwieten et al., 2010). The effect of differences in biochar feedstock, processing, and physical properties between experiments is not known.
Plant establishment and growth study data are often collected as plant height (Graber et al., 2010; Sun et al., 2014; Vaughn et al., 2013), dry weight (Alburquerque et al., 2014; Chan et al., 2008; Deenik et al., 2010; Free et al., 2010; Graber et al., 2010; Van Zwieten et al., 2010; Vaughn et al., 2013), root length (Free et al., 2010; Solaiman et al., 2012), or leaf area (Graber at al., 2010; Paneque et al., 2016). Herbaceous perennial seedling dry weights are often less than 1 mg (Fenner, 1983; Gross, 1984), resulting in tedious laboratory work with samples that are difficult to retain after weighing. One alternative to dry weight analysis is digital imaging, which is less tedious and allows for lasting records of samples (Judd et al., 2015).
Digital imaging and analysis have been used to quantify plant growth in micropropagation (Smith et al., 1989), aquatic plant establishment (Sher-Kaul et al., 1995), and in plant phenotyping studies (Golzarian et al., 2011; Leister et al., 1999). The equipment and software required ranged widely and in some cases, the software may be free (Tajima and Kato, 2011). Digital imaging allows seedling length and two-dimensional area data to be easily calculated with software. To date, most biochar studies with plant growth rely on weight or length measurement data as dependent variables, so it is important to understand how two-dimensional area data correlate with these metrics.
Biochar use in container plant production is promising, but more research is needed in the context of ornamental plant propagation. The species in this study were selected from the ornamental perennial plant industry (Coreopsis grandiflora Hogg ex Sweet ‘Early Sunrise’ and Leucanthemum ×superbum Bergman ex J. Ingram ‘Silver Princess’) and the restoration and revegetation industry (Eschscholzia californica Cham.; Montalvo et al., 2002) because their germination and seedling establishment responses to a PCM have not been documented. The primary objective was to assess the effects of coconut shell biochar in propagation substrate on seed germination and seedling growth for these three species. A secondary objective was to examine the relationship between digital imaging data and traditional, manually collected data.
Alburquerque, J.A., Calero, J.M., Barron, V., Torrent, J., del Campillo, M.C., Gallardo, A. & Villar, R. 2014 Effects of biochars produced from different feedstocks on soil properties and sunflower growth J. Plant Nutr. Soil Sci. 177 1 16 25
Bamberg, J.B., Hanneman, R.E. Jr & Towill, L.E. 1986 Use of activated charcoal to enhance the germination of botanical seeds of potato Amer. Potato J. 63 4 181 189
Baskin, C.C. & Baskin, J.M. 2014 Seeds: Ecology, biogeography, and evolution of dormancy and germination. 2nd ed. Academic Press, New York, NY
Bewley, J.D., Bradford, K.J., Hilhorst, H.W.M. & Nonogaki, H. 2013 Seeds: Physiology of development, germination and dormancy. Springer, New York, NY
Brown, R., del Campo, D., Boateng, A.A., Garcia-Perez, M. & Masek, O. 2015 Fundamentals of biochar production, p. 39–62. In: J. Lehmann and S. Joseph (eds.). Biochar for environmental management: Science and technology. Routledge, New York, NY
Camps-Arbestain, M., Amonette, J.E., Singh, B., Wang, T. & Schmidt, H.P. 2015 A biochar classification system and associated test methods, p. 165–194. In: J. Lehmann and S. Joseph (eds.). Biochar for environmental management: Science and technology. Routledge, New York, NY
Chan, K.Y., Van Zwieten, L., Meszaros, I., Downie, A. & Joseph, S. 2008 Using poultry litter biochars as soil amendments Austral. J. Soil Res. 46 5 437 444
Deenik, J.L., McClellan, T., Uehara, G., Antal, M.J. Jr & Campbell, S. 2010 Charcoal volatile matter content influences plant growth and soil nitrogen transformations Soil Sci. Soc. Amer. J. 74 4 1259 1270
Dumroese, R.K., Heiskanen, J., Englund, K. & Tervahauta, A. 2011 Pelleted biochar: Chemical and physical properties show potential use as a substrate in container nurseries Biomass Bioenergy 35 2018 2027
Fenner, M. 1983 Relationships between seed weight, ash content and seedling growth in twenty-four species of Compositae New Phytol. 95 4 697 706
Fitzer, E., Kochling, K-H., Boehm, H.P. & Marsh, H. 1995 Recommended terminology for the description of carbon as a solid Pure Appl. Chem. 67 3 473 506
Free, H.F., McGill, C.R., Rowarth, J.S. & Hedley, M.J. 2010 The effects of biochars on maize (Zea mays) germination N. Z. J. Agr. Res. 53 1 1 4
Golzarian, M.R., Frick, R.A., Rajendran, K., Berger, B., Roy, S., Tester, M. & Lun, D.S. 2011 Accurate inference of shoot biomass from high-throughput images of cereal plants Plant Methods 7 2 1 11
Graber, E.R., Harel, Y.M., Kolton, M., Cytryn, E., Silber, A., David, D.R., Tsechansky, L., Borenshtein, M. & Elad, Y. 2010 Biochar impact on development and productivity of pepper and tomato grown in fertigated soilless media Plant Soil 337 1 481 496
Gray, M., Johnson, M.G., Dragila, M.I. & Kleber, M. 2014 Water uptake in biochars: The roles of porosity and hydrophobicity Biomass Bioenergy 61 1 196 205
Gross, K.L. 1984 Effects of seed size and growth form on seedling establishment of six monocarpic perennial plants J. Ecol. 72 2 369 387
Hartmann, H.T., Kester, D.E., Davies, F.T. Jr & Geneve, R.L. 2011 Hartmann and Kester’s plant propagation: Principles and practice. 8th ed. Pearson, Saddle River, NJ
Headlee, W., Brewer, C.E. & Hall, R.B. 2014 Biochar as a substitute for vermiculite in potting mix for hybrid poplar BioEnergy Res. 7 1 120 131
Judd, L.A., Jackson, B.E. & Fonteno, W.C. 2015 Advancements in root growth measurement technologies and observation capabilities for container-grown plants Plants 4 3 369 392
Keeley, S.C. & Pizzorno, M. 1986 Charred wood stimulated germination of two fire-following herbs of the California chaparral and the role of hemicellulose Amer. J. Bot. 73 9 1289 1297
Kinney, T.J., Masiello, C.A., Dugan, B., Hockaday, W.C., Dean, M.R., Zygourakis, K. & Barnes, R.T. 2012 Hydrologic properties of biochars produced at different temperatures Biomass Bioenergy 41 1 34 43
Landis, T.D. & Morgan, N. 2009 Growing media alternatives for forest and native plant nurseries, p. 26–31. In: R.K. Dumroese and L.E. Riley (tech. cords.). Natl. Proc.: Forest and Conservation Assn. 2008 Proc. RMRS-P-58. U.S. Dept. Agr. For. Serv., Rocky Mountain Res. Sta., Fort Collins, CO
Lehmann, J. & Joseph, S. 2015 Biochar for environmental management: An introduction, p. 1–14. In: J. Lehmann and S. Joseph (eds.). Biochar for environmental management: Science and technology. Routledge, New York, NY
Leister, D., Varotto, C., Pesaresi, P., Niwergall, A. & Salamini, F. 1999 Large-scale evaluation of plant growth in Arabidopsis thaliana by non-invasive image analysis Plant Physiol. Biochem. 37 9 671 678
Liao, S., Pan, B., Li, H., Zhang, D. & Xing, B. 2014 Detecting free radicals in biochars and determining their ability to inhibit the germination and growth of corn, wheat, and rice seedlings Environ. Sci. Technol. 48 15 8581 8587
Liopa-Tsakalidi, A. & Barouchas, P.E. 2017 Effects of biochar on pepperoncini (Capsicum annuum L cv. Stavros) germination and seeding growth in two soil types Austral. J. Crop Sci. 11 3 264 270
McLaughlin, H., Anderson, P.S., Shields, F.E. & Reed, T.B. 2009 All biochars are not created equal, and how to tell them apart. Version 2. North Amer. Biochar Conf., Boulder, CO. 16 Aug. 2016. <http://www.biochar-international.org/sites/default/files/All-Biochars–Version2–Oct2009.pdf/>.
Montalvo, A.M., Feist-Alvey, L.J. & Koehler, C.E. 2002 The effect of fire and cold treatments on seed germination of annual and perennial populations of Eschscholzia californica (Papaveraceae) in southern California Madrono 49 4 207 227
Nair, A. & Carpenter, B. 2016 Biochar rate and transplant trat cell number have implications on pepper growth during transplant production HortTechnology 26 713 719
Nau J. 2011 Ball redbook, 18 ed. Vol. 2: Crop production. Ball Publishing, West Chicago, IL
Northup, J. 2013 Biochar as a replacement for perlite in greenhouse soilless substrates. Graduate theses and dissertations. Iowa State Univ. Paper 13399
Owen, W.G., Jackson, B.E., Whipker, B.E. & Fonteno, W.C. 2016 Pine wood chips as an alternative to perlite in greenhouse substrates: Nitrogen requirements HortTechnology 26 199 205
Paneque, M., De la Rosa, J.M., Franco-Navarro, J.D., Colmenero-Flores, J.M. & Knicker, H. 2016 Effect of biochar amendment on morphology, productivity and water relations of sunflower plants under non-irrigation conditions Catena 147 1 280 287
Rasband, W. 2006 Measure and label. 4 Aug. 2014. <https://imagej.nih.gov/ij/plugins/measure-label.html>.
Santiago, A. & Santiago, L. 1989 Charcoal chips as a practical substrate for container horticulture in the humid tropics Acta Hort. 238 1 141 148
Sher-Kaul, S., Oertli, B., Castella, E. & Lachavanne, J. 1995 Relationship between biomass and surface area of six submerged aquatic plant species Aquat. Bot. 51 1–2 147 154
Sileshi, G.W. 2012 A critique of current trends in the statistical analysis of seed germination and viability data Seed Sci. Res. 22 3 145 159
Smith, M.A.L., Spomer, L.A., Meyer, M.J. & McClelland, M.T. 1989 Non-invasive image analysis evaluation of growth during plant micropropagation Plant Cell Tissue Organ Cult. 19 2 91 102
Solaiman, Z.M., Murphy, D.V. & Abbott, L.K. 2012 Biochars influence seed germination and early growth of seedlings Plant Soil 353 1 273 287
Sun, Y., Gao, B., Yao, Y., Fang, J., Zhang, M., Zhou, Y., Chen, H. & Yang, L. 2014 Effects of feedstock type, production method, and pyrolysis temperature on biochar and hydrochar properties Chem. Eng. J. 240 1 574 578
Tajima, R. & Kato, Y. 2011 Comparison of threshold algorithms for automatic image processing of rice roots using freeware ImageJ Field Crops Res. 121 3 460 463
U.S. Department of Agriculture 2016 Floriculture crops 2015 summary. Natl. Agr. Stat. Serv., Washington, DC
Van Zwieten, L., Kimber, S., Morris, S., Chan, K.Y., Downie, A., Rust, J., Joseph, S. & Cowie, A. 2010 Effects of biochar from slow pyrolysis of papermill waste on agronomic performance and soil fertility Plant Soil 327 1 235 246
Vaughn, S.F., Kenar, J.A., Thompson, A.R. & Peterson, S.C. 2013 Comparison of biochars derived from wood pellets and pelletized wheat straw as replacements for peat in potting substrates Ind. Crops Prod. 51 1 437 443