Modelling the potential for soil carbon sequestration using biochar from sugarcane residues in Brazil.

Sugarcane (Saccharum officinarum L.) cultivation leaves behind around 20 t ha-1 of biomass residue after harvest and processing. We investigated the potential for sequestering carbon (C) in soil with these residues by partially converting them into biochar (recalcitrant carbon-rich material). First, we modified the RothC model to allow changes in soil C arising from additions of sugarcane-derived biochar. Second, we evaluated the modified model against published field data, and found satisfactory agreement between observed and predicted soil C accumulation. Third, we used the model to explore the potential for soil C sequestration with sugarcane biochar in São Paulo State, Brazil. The results show a potential increase in soil C stocks by 2.35 ± 0.4 t C ha-1 year-1 in sugarcane fields across the State at application rates of 4.2 t biochar ha-1 year-1. Scaling to the total sugarcane area of the State, this would be 50 Mt of CO2 equivalent year-1, which is 31% of the CO2 equivalent emissions attributed to the State in 2016. Future research should (a) further validate the model with field experiments; (b) make a full life cycle assessment of the potential for greenhouse gas mitigation, including additional effects of biochar applications on greenhouse gas balances.

Characterising the biophysical, economic and social impacts of soil carbon sequestration as a greenhouse gas removal technology.

To limit warming to well below 2°C, most scenario projections rely on greenhouse gas removal technologies (GGRTs); one such GGRT uses soil carbon sequestration (SCS) in agricultural land. In addition to their role in mitigating climate change, SCS practices play a role in delivering agroecosystem resilience, climate change adaptability and food security. Environmental heterogeneity and differences in agricultural practices challenge the practical implementation of SCS, and our analysis addresses the associated knowledge gap. Previous assessments have focused on global potentials, but there is a need among policymakers to operationalise SCS. Here, we assess a range of practices already proposed to deliver SCS, and distil these into a subset of specific measures. We provide a multidisciplinary summary of the barriers and potential incentives towards practical implementation of these measures. First, we identify specific practices with potential for both a positive impact on SCS at farm level and an uptake rate compatible with global impact. These focus on: (a) optimising crop primary productivity (e.g. nutrient optimisation, pH management, irrigation); (b) reducing soil disturbance and managing soil physical properties (e.g. improved rotations, minimum till); (c) minimising deliberate removal of C or lateral transport via erosion processes (e.g. support measures, bare fallow reduction); (d) addition of C produced outside the system (e.g. organic manure amendments, biochar addition); (e) provision of additional C inputs within the cropping system (e.g. agroforestry, cover cropping). We then consider economic and non-cost barriers and incentives for land managers implementing these measures, along with the potential externalised impacts of implementation. This offers a framework and reference point for holistic assessment of the impacts of SCS. Finally, we summarise and discuss the ability of extant scientific approaches to quantify the technical potential and externalities of SCS measures, and the barriers and incentives to their implementation in global agricultural systems.

Passive CO2 removal in urban soils: Evidence from brownfield sites.

Management of urban brownfield land can contribute to significant removal of atmospheric CO2 through the development of soil carbonate minerals. However, the potential magnitude and stability of this carbon sink is poorly quantified as previous studies address a limited range of conditions and short durations. Furthermore, the suitability of carbonate-sequestering soils for construction has not been investigated. To address these issues we measured total inorganic carbon, permeability and ground strength in the top 20 cm of soil at 20 brownfield sites in northern England, between 2015 and 2017. Across all sites accumulation occurred at a rate of 1-16 t C ha-1 yr-1, as calcite (CaCO3), corresponding to removal of approximately 4-59 t CO2 ha-1 yr-1, with the highest rate in the first 15 years after demolition. C and O stable isotope analysis of calcite confirms the atmospheric origin of the measured inorganic carbon. Statistical modelling found that pH and the content of fine materials (combined silt and clay content) were the best predictors of the total inorganic carbon content of the samples. Measurement of permeability shows that sites with carbonated soils possess a similar risk of run-off or flooding to sandy soils. Soil strength, measured as in-situ bearing capacity, increased with carbonation. These results demonstrate that the management of urban brownfield land to retain fine material derived from concrete crushing on site following demolition will promote calcite precipitation in soils, and so offers an additional CO2 removal mechanism, with no detrimental effect on drainage and possible improvements in strength. Given the large area of brownfield land that is available for development, the contribution of this process to CO2 removal by urban soils needs to be recognised in CO2 mitigation policies.

A comparative study on biochar properties and Cd adsorption behavior under effects of ageing processes of leaching, acidification and oxidation.

Biochar has potential to control the bioavailability and migration of potentially toxic heavy metals in soil by adsorption. Natural ageing in the environment may change the physicochemical properties and adsorption function of biochar over the long-term. The present study compared the effects of different simulated ageing treatments on Cd adsorption of high and low temperature biochar from straw of corn (Zea mays). Fresh and aged biochars were systematically characterized by elemental analysis, FTIR, XPS, Zeta, SEM-EDS, XRD and the composition of their mineral ash. The adsorption of Cd to fresh and aged biochars was then assessed under the influence of pH. Drawing the results together the effects of ageing on the extent and mode of Cd adsorption could be elucidated. The results showed that the adsorption capacity of fresh biochar produced at 650 °C was higher than of biochar made at 350 °C, and that mineral co-precipitation plays a dominant role in Cd sorption. Leaching removed organic and inorganic ash components from biochars, markedly diminishing the capacity of the high temperature biochar to adsorb Cd. The adsorption performance of the low temperature biochar was dependent on surface complexation. The adsorption capacity of low-temperature biochar was markedly enhanced by oxygen-containing functional groups formed through acidification and oxidation. The long-term benefits of biochar in the management of polluted soil require a rethink, considering the contrasting ageing behavior of different temperature biochar and their response to different ageing environments.

Oxidative ageing induces change in the functionality of biochar and hydrochar: Mechanistic insights from sorption of atrazine.

One attraction of using hydrochar (HC) and biochar (BC) in soil is their intrinsic affinity for organic contaminants. Oxidative ageing is likely to induce changes in physicochemical properties and functionality. To explore the long-term potential trajectories for corn stalk HC and BC to adsorb organic pollutants, we employed HC and BC exposure in 5% H2O2 to simulate oxidative ageing and get insights into mechanisms of atrazine adsorption on fresh and artificially aged materials. The physicochemical properties of fresh and aged materials were systematically compared using elemental analysis, SSA, FTIR, XPS and SEM-EDS, alongside K2Cr2O7/H2SO4 treatment to assess chemical oxidation stability. Atrazine is a typical herbicide chemical and hydrophobic organic pollutant. Adsorption isotherms of atrazine were used to reveal differences in mechanisms of sorption to BC and HC, by assessment before and ageing. BC freshly produced at 650 °C displayed higher capacity for atrazine sorption than BC produced at 500 °C, with a dominant role for π-π EDA interactions. The sorption capacity of HC freshly produced at 250 °C was higher than for HC produced at 200 °C HC, owing to higher C content and atrazine partitioning into the organic phase. Ageing increased the surface abundance of oxygenated functional groups for BC and HC and diminished bulk aromaticity. After ageing, atrazine sorption by high temperature BC was lower, but for HC it was increased. Such divergent effects must be considered when developing strategies to co-manage contaminants and carbon through the addition of carbonized materials to land.

New insights into contrasting mechanisms for PAE adsorption on millimeter, micron- and nano-scale biochar.

Biochar is being examined as a potential sorbent for organic pollutants in the environment including phthalate esters (PAEs). It has been noted that nano-scale biochar particles displayed stronger migration potential than other particles, which poses the potential risk of pollutant transfer through the environment. In this present study, we examined the influence of sub-millimeter (200-600 µm), micron-scale (10-60 µm), and nano-scale (0.1-0.6 µm) biochar on diethyl phthalate (DEP, as a model) adsorption using particles derived from corn straw and rice husk biochar. Meanwhile, the interaction between adsorption capacity and initial pH was also considered. Our results showed that the adsorption capacity of biochar for DEP increased with decreasing particle size, and was considerably higher for nano-scale biochar than for other particles. This was attributable to its developed pore structure and higher specific surface area (SSA), especially the dominant micropore (292.73 m2/g), suggesting that the adsorption of DEP to nano-scale biochar was dominated by pore-filling rather than π-π EDA and H bonding that was applied to biochar of larger, more typical dimensions. The adsorption capacity of nano-scale biochar for DEP was markedly decreased when initial pH was decreased from 9.0 to 3.0. Because an acid environment could reduce the absolute surface charge on nano-scale biochar, it was easier for the particles to agglomerate. Nano-scale biochar therefore have higher activity in alkaline conditions, which could pose certain risks through their application into the environment.

Driving forces and barriers in the removal of phosphorus from water using crop residue, wood and sewage sludge derived biochars.

The removal of phosphorus (P) from sewage effluents is necessary to control eutrophication in receiving waters. Biochar has been proposed and is investigated for the capture and reuse of P, however the forces driving and limiting P adsorption are still largely unclear. To identify the forces governing P uptake by biochar, biochars with markedly different physicochemical characteristics derived from a variety of biomass (oilseed rape straw, wheat straw, miscanthus straw, rice husk, soft wood and sewage sludge residue), pyrolysed at various temperatures, were investigated. The biochar samples were characterised in terms of pH, electrical conductivity, total acidity, carbon chemistry, metal composition, surface area, and porosity, and the uptake and release of P was compared to the biochar properties using multivariate analysis. Uptake of P by the biochars as such was low (< 0.71 mg P/g biochar with feed solutions of 50 mg P/l) and, among the variables studied, the biochars' Ca and Mg content was key in P removal and found to be pH dependant. Enhancement of biochar surface area and porosity was carried out by activation with CO2 at 800 °C and the uptake significantly improved (p < 0.05) (i.e. an increased surface area from <20 m2/g up to 781 m2/g gave a limited improvement in P removal to <1.2 mg P/g biochar at feed level of 50 mg P/l). These results confirm that the potential to use these unmodified biochars derived from a variety of biomass for P sorption is low, but that the material provides properties that may be modified or enhanced to increase sorption capacity. This study indicates that biochar/biochar feedstock with greater content of Ca and Mg will be more advantageous for P capture.

Adsorption and reductive degradation of Cr(VI) and TCE by a simply synthesized zero valent iron magnetic biochar.

To address inorganic and organic contaminants in the environment, economic new adsorbents are required. Here we test magnetic biochar for efficient capture of the typical pollutants Cr(VI) and trichloroethylene (TCE) from solution. We used a simple synthesis using 2M FeCl3 solution and peanut hull biomass to prepare magnetic ZVI biochar at alternate pyrolysis temperatures between 650 and 800 °C. The physicochemical character of the biochars were assessed using X-ray diffraction (XRD) and the Brunauer-Emmett-Teller (BET) method for surface area. The magnetic ZVI biochars were highly effective in the removal of Cr(VI) and TCE. The most effective magnetic biochar produced at 800 °C was further examined using scanning electron microscopy (SEM), revealing a high and even loading of ZVI. After sorption the same magnetic biochar was examined by X-ray photoelectron spectroscopy (XPS) to ascertain the underlying mechanisms. The dependence of Cr(VI) capture on solution pH was also examined. Our interpretation suggests that when pH < pHzpc (2.5) electrostatic attraction and redox reactions dominated the adsorption of Cr(VI). When pH > pHzpc the removal process was controlled mainly by redox reaction and substitution of chromate anions for hydroxyl (OH) groups. Capture of TCE in contrast involved hydrophobic partitioning, pore-filling and reductive degradation. Overall our results suggest that simple synthesis of magnetic ZVI biochar could offer an economic and effective option to address water contamination issues.

Biochar Phosphorus Release Is Limited by High pH and Excess Calcium.

Aside from its use for improving soil properties, biochar is increasingly promoted as a direct nutrient provider for sustainable recycling of waste materials. However, incomplete understanding of the interacting factors that determine P release from biochar may limit the efficiency of P recycling from biochar to soil. In particular, the contrasting pH of biochar and soil need to be considered. In this study, soil-free biochar (rice [ L.] husk, 700°C) extractions were performed under different pH (4.6-9.9) and extractant conditions to test how solution composition affects biochar P release. When solution pH was in the range of 7.6 to 8.6 and excess Ca was present in the solution or in biochar, P release was low-only 1 to 7% of the total P was released compared with ∼20% under most other conditions. Importantly, we demonstrate that biochar total Ca concentration is closely related to P availability ( = 0.76) and could be used to predict biochar P release. The results suggest that for maximum P release, low Ca concentrations in biochar and (soil) solution are needed and/or a pH <7.5 at the soil-biochar interface. This novel understanding will help engineer sustainable biochar fertilizers optimized for P provision.

Insight into mechanism of aged biochar for adsorption of PAEs: Reciprocal effects of ageing and coexisting Cd2.

Biomass derived biochar is a stable carbon-rich product with potential for soil amendment. Introduced into the natural environment, biochar will naturally experience 'ageing' processes that are liable to change its physicochemical properties and the mobility of sorbed pollutants over the longer term. To elucidate the reciprocal effects of biochar ageing and heavy metal adsorption on the affinity of biochar for organic pollutants, we systematically assessed the adsorption of diethyl phthalate (DEP), representative of phthalic acid esters (PAEs), to fresh and aged biochars with and without coexistence of Cd2+. Long-term oxidative ageing was simulated using 5% H2O2 and applied to biochar samples made from corn cob, maize straw and wheat straw made by pyrolysis at both 450 °C and 650 °C. Our results showed that biochar made at lower temperature (450 °C) and from straw exhibited the higher adsorption capacity, owing to their greater polarity and abundance of O-containing functional groups. The adsorption of DEP onto fresh biochars was found to be driven by van der Waals force and H-bonding. Biochar made at the higher temperature (650 °C) displayed higher carbon stability than that produced at lower pyrolysis temperature. Oxidized biochar showed lower adsorption capacity than fresh biochar owing to the formation of three-dimensional water clusters on biochar surface, which blocked accessible sites and decreased the H-bonding effect between DEP and biochars. The coexistence of Cd2+ suppressed the sorption of DEP, via competition for the same electron-rich sites. This indicates that cation/π-π EDA interactions are the primary mechanism for PAE and Cd2+ stabilization on biochar. Our study sheds light on the mechanism of organic pollutant sorption by biochar, as well as the potential susceptibilities of this sorption to ageing effects in the natural environment.

Trends in the recovery of phosphorus in bioavailable forms from wastewater.

Addressing food security issues arising from phosphorus (P) scarcity is described as one of the greatest global challenges of the 21st Century. Dependence on inorganic phosphate fertilisers derived from limited geological sources of P creates an urgent need to recover P from wastes and treated waters, in safe forms that are also effective agriculturally - the established process of P removal by chemical precipitation using Fe or Al salts, is effective for P removal but leads to residues with limited bioavailability and contamination concerns. One of the greatest opportunities for P recovery is at wastewater treatment plants (WWTPs) where the crystallisation of struvite and Ca-P from enhanced biological P removal (EBPR) sludge is well developed and already shown to be economically and operationally feasible in some WWTPs. However, recovery through this approach can be limited to <25% efficiency unless chemical extraction is applied. Thermochemical treatment of sludge ash produces detoxified residues that are currently utilised by the fertiliser industry; wet chemical extraction can be economically feasible in recovering P and other by-products. The bioavailability of recovered P depends on soil pH as well as the P-rich material in question. Struvite is a superior recovered P product in terms of plant availability, while use of Ca-P and thermochemically treated sewage sludge ash is limited to acidic soils. These technologies, in addition to others less developed, will be commercially pushed forward by revised fertiliser legislation and foreseeable legislative limits for WWTPs to achieve discharges of <1 mg P/L.

Biochar and enhanced phosphate capture: Mapping mechanisms to functional properties.

A multi-technique analysis was performed on a range of biochar materials derived from secondary organic resources and aimed at sustainable recovery and re-use of wastewater phosphorus (P). Our purpose was to identify mechanisms of P capture in biochar and thereby inform its future optimisation as a sustainable P fertiliser. The biochar feedstock comprised pellets of anaerobically digested sewage sludge (PAD) or pellets of the same blended in the ratio 9:1 with ochre sourced from minewater treatment (POCAD), components which have limited alternative economic value. In the present study the feedstocks were pyrolysed at two highest treatment temperatures of 450 and 550 °C. Each of the resulting biochars were repeatedly exposed to a 20 mg l-1 PO4-P solution, to produce a parallel set of P-exposed biochars. Biochar exterior and/or interior surfaces were quantitatively characterised using laser-ablation (LA)-ICP-MS, X-ray diffraction, X-ray photo-electron spectroscopy (XPS) and scanning electron microscopy coupled with energy dispersive X-ray. The results highlighted the general importance of Fe minerals in P capture. XPS analysis of POCAD550 indicated lower oxidation state Fe2p3 bonding compared to POCAD450, and LA-ICP-MS indicated stronger covariation of Fe and S, even after P exposure. This suggests that low-solubility Fe/S compounds are formed during pyrolysis, are affected by process parameters and impact on P capture. Other data suggested capture roles for aluminium, calcium and silicon. Overall, our analyses suggest that a range of mechanisms for P capture are concurrently active in biochar. We highlighted the potential to manipulate these through choice of form and composition of feedstock as well as pyrolysis processing, so that biochar may be increasingly tailored towards specific functionality.

Bioavailability of phosphorus, other nutrients and potentially toxic elements from marginal biomass-derived biochar assessed in barley (Hordeum vulgare) growth experiments.

Biochars produced from marginal biomass feedstocks are a potential source of recycled nutrients for agriculture, but may also contain potentially toxic elements (PTEs) which can cause phytotoxicity. We assessed the potential for nutrient recycling from such materials against potential environmental risks in 17 biochars containing high concentrations of various PTEs and nutrients. Methods for investigating the risk of biochar-derived PTEs were developed and assessed. Short-term (21days) growth experiments with barley (Hordeum vulgare) in 5% biochar/sand mixtures were used to present the 'worst-case scenario' of high dose and low pH buffering. We compared plant nutrient and PTE concentrations with amounts extracted from the same biochars using 1M NH4NO3 or 0.01M CaCl2 (buffered and unbuffered, respectively) and Mehlich 3 to analyse whether such extractions could be used to predict bioavailability. The yields of barley grown with biochars "EPOCAD550", and "WLB550" were significantly higher than the control (p<0.05). Total phosphorus (P) concentration in above-ground biomass was higher than the control for the EPOCAD550 treatment (p<0.01). Both buffered and unbuffered 0.01M CaCl2 biochar extractions were significantly positively correlated with plant leaf concentration for six of the 18 elements investigated, more than any of the other extractions. CaCl2 extractions provided the most representative assessment of element bioavailability from marginal biochars compared to more resource-intensive growth experiments. Our results provide new insights into the bioavailability of elements in biochar and the standardisation of methods which accurately assess this attribute, which is necessary for promoting use of biochars from marginal biomass for recycling nutrients from wastewater and to agricultural production.

Optimising the recovery and re-use of phosphorus from wastewater effluent for sustainable fertiliser development.

Recovery and re-use of phosphorus (P) from wastewater treatment systems as agricultural fertiliser presents an important and viable target for P waste reduction and recycling. In this study novel biochar materials for P filtration of wastewater were designed and produced using waste feedstocks, with consideration of the plant accessibility of the P captured by the biochars. The biochars were produced using batch slow pyrolysis at 450 °C and 550 °C from a) AD: anaerobically digested sewage sludge and b) OCAD: a 1:1 mixture of anaerobically digested sewage sludge and ochre, a mineral product from mine drainage treatment. A set of experiments was designed using pH buffering to provide a robust framework for assessing the P recovery capacity and affinity of the biochars compared to other potential P recovery materials (unprocessed ochre, activated carbon and zeolite). After 5 days of repeated exposure to a P solution at a wastewater-relevant concentration (0.02 g P l(-1)) replenished each 24 h, relatively high masses of P were recovered by ochre (1.73 ± 8.93×10(-3) mg P g(-1)) and the biochars OCAD550 (1.26 ± 4.66×10(-3) mg P g(-1)), OCAD450 (1.24 ± 2.10×10(-3) mg P g(-1)), AD450 (1.06 ± 3.84×10(-3) mg P g(-1)), and AD550 (0.986 ± 9.31×10(-3) mg P g(-1)). The biochar materials had higher removal rates than both activated carbon (0.884 ± 1.69×10(-2) mg P g(-1)) and zeolite (0.130 ± 1.05×10(-2) mg P g(-1)). To assess the extractability of recovered P, P exposure was followed by repeated extraction for 4 days with pH 7-buffered deionised water. The AD biochars retained 55% of the P recovered, OCAD biochars 78% and ochre 100%. Assessment of potentially toxic element concentrations in the biochars against guideline values indicated low risk associated with their use in the environment. Our successful demonstration of biochar materials highlights the potential for further development of P filters for wastewater treatment systems from anaerobic digestate produced and pyrolysed on-site with energy recovery.

Adsorption kinetics of magnetic biochar derived from peanut hull on removal of Cr (VI) from aqueous solution: Effects of production conditions and particle size.

Magnetic biochar was made from peanut hull biomass using iron chloride in a simplified aqueous phase approach and pyrolysis at alternative peak temperatures (450-650 °C). Magnetic biochar showed an extreme capacity for adsorption of hexavalent chromium Cr (VI) from aqueous solution, which was 1-2 orders of magnitude higher compared to standard (non-magnetic) biochar from the same feedstock. Adsorption increased with pyrolysis temperature peaking at 77,542 mg kg(-1) in the sample pyrolysed at 650 °C. In contrast to magnetic biochar, the low adsorption capacity of standard biochar decreased with increasing pyrolysis temperature. The fine particle size of magnetic biochar and low aqueous pH were also important for adsorption. Surfaces of products from batch adsorption experiments were characterized by scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction, X-ray photoelectron spectroscopy and vibrating sample magnetometer. This revealed that γ-Fe2O3 was crucial to the properties (adsorbance and magnetism) of magnetic biochar. The removal mechanism was the Cr (VI) electrostatic attracted on protonated -OH on γ-Fe2O3 surface and it could be desorbed by alkaline solution. Findings suggest that pyrolysis has potential to create effective, magnetically recoverable adsorbents relevant to environmental application.

Toward the Standardization of Biochar Analysis: The COST Action TD1107 Interlaboratory Comparison.

Biochar produced by pyrolysis of organic residues is increasingly used for soil amendment and many other applications. However, analytical methods for its physical and chemical characterization are yet far from being specifically adapted, optimized, and standardized. Therefore, COST Action TD1107 conducted an interlaboratory comparison in which 22 laboratories from 12 countries analyzed three different types of biochar for 38 physical-chemical parameters (macro- and microelements, heavy metals, polycyclic aromatic hydrocarbons, pH, electrical conductivity, and specific surface area) with their preferential methods. The data were evaluated in detail using professional interlaboratory testing software. Whereas intralaboratory repeatability was generally good or at least acceptable, interlaboratory reproducibility was mostly not (20% < mean reproducibility standard deviation < 460%). This paper contributes to better comparability of biochar data published already and provides recommendations to improve and harmonize specific methods for biochar analysis in the future.

Biochar diminishes nitrous oxide and nitrate leaching from diverse nutrient sources.

Manure generated by intensive livestock operations poses potential ecological risk in the form of water pollution and greenhouse gas emission. To assess the impact of biochar on coarse-textured soils under contrasting nutrient management regimes, a 55-d incubation was conducted using unplanted soil columns amended with manure, slurry, or fertilizer (plus unamended control), each with or without biochar applied at 2% soil mass (dry weight basis). Under repeated leaching, the cumulative NO emission from the columns was significantly affected by the presence of biochar ( < 0.0001), although these data were not normally distributed. Results indicated that the biochar-amended soils emitted significantly less NO than their unamended counterparts, with the exception of manure-amended soils. The presence of biochar increased the pH of column leachate by 0.08 to 1.70 and significantly decreased the cumulative amount of mineral N leached from the soil. The presence of biochar significantly increased the amount of PO-P in soil leachate, but there was no significant difference between the means for any of the amendments used on their own relative to their biochar-amended counterparts. The data demonstrate that biochar could potentially aid in the mitigation of NO emissions from certain soils and in N loss in leachate from soil amended with slurry, manure, or fertilizer used in livestock systems.

How much land-based greenhouse gas mitigation can be achieved without compromising food security and environmental goals?

Feeding 9-10 billion people by 2050 and preventing dangerous climate change are two of the greatest challenges facing humanity. Both challenges must be met while reducing the impact of land management on ecosystem services that deliver vital goods and services, and support human health and well-being. Few studies to date have considered the interactions between these challenges. In this study we briefly outline the challenges, review the supply- and demand-side climate mitigation potential available in the Agriculture, Forestry and Other Land Use AFOLU sector and options for delivering food security. We briefly outline some of the synergies and trade-offs afforded by mitigation practices, before presenting an assessment of the mitigation potential possible in the AFOLU sector under possible future scenarios in which demand-side measures codeliver to aid food security. We conclude that while supply-side mitigation measures, such as changes in land management, might either enhance or negatively impact food security, demand-side mitigation measures, such as reduced waste or demand for livestock products, should benefit both food security and greenhouse gas (GHG) mitigation. Demand-side measures offer a greater potential (1.5-15.6 Gt CO2 -eq. yr(-1) ) in meeting both challenges than do supply-side measures (1.5-4.3 Gt CO2 -eq. yr(-1) at carbon prices between 20 and 100 US$ tCO2 -eq. yr(-1) ), but given the enormity of challenges, all options need to be considered. Supply-side measures should be implemented immediately, focussing on those that allow the production of more agricultural product per unit of input. For demand-side measures, given the difficulties in their implementation and lag in their effectiveness, policy should be introduced quickly, and should aim to codeliver to other policy agenda, such as improving environmental quality or improving dietary health. These problems facing humanity in the 21st Century are extremely challenging, and policy that addresses multiple objectives is required now more than ever.