Modern pyrolysis systems are used to extract liquid and gas petroleum products from biomass for fuel or other chemical products. Biochar is the charred organic matter that remains after pyrolysis of biomass or manure. Biochar is essentially the same as charcoal with the primary distinction being that biochar is intended for some form of soil or agricultural application (Lehmann and Joseph, 2009). Return of biochar to soil systems, where it is believed to be stable for hundreds or thousands of years, is touted as a promising solution to reducing atmospheric carbon (Glaser et al., 2002).
The influence of biochar in mineral soil systems has been studied and reviewed extensively (Lehmann et al., 2011; Spokas et al., 2011). Some of the most commonly cited beneficial impacts of biochar have been improved crop growth in highly weathered or sandy soils (Lehmann et al., 2003; Novak et al., 2009), increased soil pH (Novak et al., 2009), shifts to beneficial microbial populations (Lehmann et al., 2011), increased mycorrhizal associations (Warnock et al., 2007), and improved nutrient retention (Clough and Condron, 2010). Benefits of biochar are not consistently realized in temperate soils. A meta-analysis on 100 biochar studies concluded that variability in biochar source and application parameters resulted in ≈20% negative results, 30% nonsignificant difference in results, and 50% short-term positive results (Spokas et al., 2011). However, the authors of the meta-analysis caution that there was a greater number of increased yield results reported for studies that occurred in weathered or degraded soils that had prior limited fertility and productivity.
The influence of biochars on soilless substrates used in greenhouse and nursery container substrates has been studied less, and only a few citations tangentially related to greenhouse and nursery production in soilless substrates are available. Kadota and Niimi (2004) reported 10% or 30% additions of biochar combined with either pyroligneous acid (wood vinegar) or barnyard manure to a 2:1:1:1:1 peatmoss:soil:vermiculite:perlite:sand (v/v) substrate had either no effect or minor changes (positive and negative) in growth parameters of several bedding plant species. Graber et al. (2010) reported that biochar improved growth and productivity of pepper (Capsicum annuum L.) and tomato (Lycopersicum esculentum Mill.) plants in a blend of coconut fiber and tuff and attributed improvements to either stimulated shifts in microbial populations toward beneficial plant growth-promoting rhizobacteria or fungi or low doses of phytotoxic biochar chemicals, which may have stimulated plant growth at low doses. Ruamrungsri et al. (2011) reported that gloriosa lily (Gloriosa rothschildiana L.) in a 1:1:1 sand:rice husk charcoal:coconut fiber substrate did not respond to varying levels of applied calcium (Ca) fertilizers as a result of high Ca levels in rice husk charcoal. Santiago and Santiago (1989) briefly summarized their work using wood-based charcoal chips for hydroponic culture in humid tropical regions of Asia but provided few details other than plants grew well when fertilized with resin-coated fertilizers. Dumroese et al. (2011) evaluated pelletized biochar (pellets were 43% biochar, 43% wood flour, 7% polyacetic acid, and 7% starch) in combination with sphagnum peatmoss for production of forest seedlings. They found that amendment with 25% biochar pellets improved hydraulic conductivity and water retention at high matric potentials and beneficially increased substrate pH, although concern was noted about lower cation exchange capacity and higher carbon:nitrogen ratio. Beck et al. (2011) showed that amendment of an unspecified greenroof media with 7% biochar increased water retention and decreased total nitrogen and phosphorus, nitrate, phosphate, and organic carbon in runoff.
The body of biochar research in soilless substrates is far less complete than that for mineral soils; however, the collection of papers thus far seems to indicate similar potential benefits in soilless substrates including additions of some nutrients, reduction in leaching of nitrates and phosphates, beneficial shifts in microbial populations, and improved physical properties. Despite this, these articles have limited applicability to production methods typical of greenhouse production in sphagnum peatmoss substrates. The objective of this research was to determine the effect biochar additions have on nutrient dynamics in a sphagnum peatmoss-based soilless substrate typical of those used in greenhouse production of ornamental crops.
Beck, D.A., Johnson, G.R. & Spolek, G.A. 2011 Amending greenroof soil with biochar to affect runoff water quantity and quality Environ. Pollut. 159 2111 2118
Dumroese, K.R., Heiskanen, J., Englund, K. & Tervahauta, A. 2011 Pelleted biochar: chemical and physical properties show potential use as a substrate in container nurseries Biomass and Bioenergy 35 2018 2027
Glaser, B., Lehmann, J. & Zech, W. 2002 Ameliorating physical and chemical properties of highly weathered soils in the tropics with charcoal—A review Biol. Fertil. Soils 35 219 230
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 337 481 496
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