13 / RESEARCH
BIOCHAR
POTENTIAL Drs. Karen O’Hanlon and Munoo Prasad explore the exciting potential of Biochar as a plant growth promoter
B
iochar is a carbonaceous product obtained by the pyrolysis of organic materials. Pyrolysis uses high temperatures to break down biomass or waste in an oxygen-free environment. Nowadays, the pyrolysis process and Biochar are being studied as a treatment technology to convert organic wastes and by-products into organic products for use in agriculture. The interest and use of Biochar is inspired by terra preta de indio (Amazonian black earth) from the preColumbian civilization times, which were characterised by remarkable soil fertility.
KEY BENEFITS OF BIOCHAR More recently Biochar has been promoted as; ●A s a form of carbon sequestration and storage ●F or its potential benefits for bioenergy production (e.g., syngas, bio-oil and heat) ●F or use in soils including as a component of growing media to enhance crop productivity ●T o reduce nitrate leaching through nitrate and phosphate capture ●T o adsorb contaminants, such as arsenic and copper
from soils ●A s an animal feed ●F or the reduction of odour and ammonia from slurry ●T o reduce trace-gas emissions from soils (nitrous oxide
and methane) Importantly, from a climate perspective, Biochar is very persistent in the environment, and so its application to soils can remove carbon dioxide from the atmosphere for long periods of time. Thus there are exciting possibilities in using Biochar to mitigate climate change by carbon sequestration or waste management. Biochar also has great potential for the waste-processing industry as it allows for the recovery of waste (e.g. garden waste and forestry waste) as a potentially useful by-product. Other wastes (e.g. manure and sludge are not suitable if the Biochar is destined for use as a component of a growing media due to high electrical conductivity).
BIOCHAR IN GROWING MEDIA Most of the research on the use of Biochar in growing media is aimed towards its application as an alternative
to environmentally unfriendly substrates such as peat, vermiculite and perlite. These studies (including trials in Ireland) have shown that Biochar: Reduced nitrogen and phosphorus leaching The improved water efficiency of growing media Improved plant fresh weight and root development The improvement of disease resistance; and Offsetting or reversing of carbon footprints Horticulture in temperate climate zones is energy-intensive and the use of peat as the main ingredient in substrates releases additional GHG emissions during mining and processing. Increasingly restrictive legislation and wetland ecosystem destruction, through its extraction, will limit peat use. Nowadays in order to attain sustainability in potted plant production, producers are opting for peat alternatives, such as Biochar, that provide good performance, are readily available, inexpensive and environmentally friendly. Lab-scale data on Biochar carbon recalcitrance compared to peat indicate that spent Biochar-based substrates in the soil are a highly effective carbon storage tool (~80% vs. 40% respectively). The combination of bioenergy replacing fossil energy, Biochar replacing peat in the substrate and long term storage of the spent Biochar in soil all contribute substantially to GHG reductions. In order to make Biochar an effective horticultural replacement for peat, it is recommended that Biochar feedstock be standardised as well as the pyrolysis process (temperature and residence time as this affects surface area) so that growers can rely on consistent and reproducible Biochar to get the desired effect. Large scale change-over to Biochar will not occur unless there are financial incentives from government (Carbon Credits) or market incentives.
ENRICHED BIOCHAR A further enhancement to Biochar is possible due to its large surface area which acts as a natural environment for beneficial bacteria and fungi. The inclusion of plant growthpromoting bacteria (PGPB), most notably the spore former Bacillus subtilis, has the following additional benefits: ● It increases the uptake of minerals into the plant ● i t promotes plant growth ● I t modulates plant growth hormone levels
Autum/Winter 2019 / www.horticultureconnected.ie / HORTICULTURECONNECTED
45
