Biochar – synergies and trade‐offs between soil enhancing properties and C sequestration potential

Abstract

The characterization of biochar has been predominantly focused around determining physicochemical properties including chemical composition, porosity and volatile content. To date, little systematic research has been done into assessing the properties of biochar that directly relate to its function in soil and how production conditions could impact these. The aim of this study was to evaluate how pyrolysis conditions can influence biochar's potential for soil enhancing benefits by addressing key soil constraints, and identify potential synergies and restrictions. To do this, biochar produced from pine wood chips (PC), wheat straw (WS) and wheat straw pellets (WSP) at four highest treatment temperatures (HTT) (350, 450, 550 and 650°C) and two heating rates (5 and 100°C min À1 ) were analysed for pH, extractable nutrients, cation exchange capacity (CEC), stable-C content and labile-C content. Highest treatment temperature and feedstock selection played an important role in the development of biochar functional properties while overall heating rate (in the range investigated) was found to have no significant effect on pH, stable-C or labile-C concentrations. Increasing the HTT reduced biochar yield and labile-C content while increasing the yield of stable-C present within biochar. Biochar produced at higher HTT also demonstrated a higher degree of alkalinity improving biochar's ability to increase soil pH. The concentration of extractable nutrients was mainly affected by feedstock selection while the biochar CEC was influenced by HTT, generally reaching its highest values between 450-550°C. Biochar produced at ≥550°C showed high combined values for C stability, pH and CEC while lower HTTs favoured nutrient availability. Therefore attempts to maximize biochar's C sequestration potential could reduce the availability of biochar nutrients. Developing our understanding of how feedstock selection and processing conditions influence key biochar properties can be used to refine the pyrolysis process and design of 'bespoke biochar' engineered to deliver specific environmental functions.

Influence of Oil Palm Empty Fruit Bunch Biochar on Floodwater pH and Yield Components of Rice Cultivated on Acid Sulphate Soil under Rice Intensification Practices

“…However, the benefits offered by biochar is heavily influenced by two factors, type of feedstock and production condition such as heating rate, maximum temperature and residence time (Sukiran et al, 2011;Zhao et al, 2013). Thus, different types of biochar such as grass biochar are less resistant to degradation than wood biochar but it provides more nutrients to plants (Zimmerman et al, 2011;Crombie et al, 2014). In general, continuous application of biochar increases soil organic C and enhance soil properties.…”

Engineered biochar from microwave-assisted catalytic pyrolysis of switchgrass for increasing water-holding capacity and fertility of sandy soil

“…is crucial to overcome the high cost associated with the application of biochar to soil in a large scale. Most of biochar studies were conducted using biochars produced from slow pyrolysis by conventional heating, which is not favourable for industrial biochar production because of many constraints such as large equipment needed, low productivity, and high production cost (Spokas et al, 2012;Crombie et al, 2014). Biochar production cost can be reduced through utilizing proper additives/catalysts in which these additives or catalysts would serve for many functions: such as increasing microwave heating rate to reduce energy consumption, producing a high grade bio-oil that can be used as a fuel, and remaining in the produced biochar to serve as a source of nutrients (Mohamed et al, 2016).…”

“…Specific surface area and cation exchange capacity (CEC) are considered indirect measures of the ability of soils to hold water and retain nutrients (e.g., ammonium, nitrate, P, Mg and Ca), which will improve soil fertility, and bind different contaminants (Major et al, 2009;Laird et al, 2010;Crombie et al, 2014). Improving N-fertilizer use efficiency would lead to reduced fertilizer application rates, and reduced GHG emissions from the whole process, starting from the production of fertilizer to the application to soil (Major et al, 2009;Crombie et al, 2014;Wang et al, 2015).…”

“…Improving N-fertilizer use efficiency would lead to reduced fertilizer application rates, and reduced GHG emissions from the whole process, starting from the production of fertilizer to the application to soil (Major et al, 2009;Crombie et al, 2014;Wang et al, 2015). Therefore, there is an increasing need for new methods to create oxygenated biochar possessing high CEC to increase soil CEC.…”

“…Most biochars created from virgin biomass without additives possess fewer nutrients compared to conventional fertilizers. In addition, most of biochar studies focused on biochars produced from slow conventional heating methods which are not suitable for industrial production (Zimmerman, 2010;Novak et al, 2012;Kinney et al, 2012;Crombie et al, 2014). Producing biochar capable of releasing nutrients for plants is thus in great need and interest Spokas et al, 2012;Crombie et al, 2014).…”