Abstract
Peat is used as rooting medium in greenhouse horticulture. Biochar is a sustainable alternative for the use of peat, which will reduce peat derived carbon dioxide emissions. Biochar in potting soil mixtures allegedly increases water storage, nutrient supply, microbial life and disease suppression but this depends on feedstock and the production process. The aim of this paper is to find combinations of feedstock and production circumstances which will deliver biochars with value for the horticultural end user. Low-temperature (600 °C–750 °C) gasification was used for combined energy and biochar generation. Biochars produced were screened in laboratory tests and selected biochars were used in plant experiments. Tests included dry bulk density, total pore space, specific surface area, phytotoxicity, pH, EC, moisture characteristics and microbial stability. We conclude that biochars from nutrient-rich feedstocks are too saline and too alkaline to be applied in horticultural rooting media. Biochars from less nutrient-rich feedstocks can be conveniently neutralized by mixing with acid peat. The influence of production parameters on specific surface area, pH, total pore space and toxicity is discussed. Biochar mildly improved the survival of beneficial micro-organisms in a mix with peat. Overall, wood biochar can replace at least 20% v/v of peat in potting soils without affecting plant growth.
Highlights
Biochar is the carbon rich co-product of pyrolysis or gasification of biomass
The low hydrogen and nitrogen contents of
Two possible explanations of the reduced specific surface area found in sweet pepper based biochar are: (1) Clogging of internal pores by volatile tars [34]; (2) Low temperature melting of ash compounds with high levels of calcium and potassium, which is in line with slagging reported for such samples [41]
Summary
Biochar is the carbon rich co-product of pyrolysis or gasification of biomass. Biochar application to soils is of public and agricultural interest [1]. The public interest in biochar application to soil is focused on the potential to decrease global net carbon dioxide emission by an increased soil storage of carbon [2]. Just as for agriculture, biochar application to horticultural rooting media (soilless substrates) is of public and agricultural interest. (1) The public interest is to use biochars from renewable organic residual streams to substitute part of the peat used in rooting media in greenhouse horticulture [10,11].
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