Various studies have established that feedstock choice, pyrolysis temperature, and pyrolysis type influence final biochar physicochemical characteristics. However, overarching analyses of pre-biochar creation choices and correlations to biochar characteristics are severely lacking. Thus, the objective of this work was to help researchers, biochar-stakeholders, and practitioners make more well-informed choices in terms of how these three major parameters influence the final biochar product. Utilizing approximately 5400 peer-reviewed journal articles and over 50,800 individual data points, herein we elucidate the selections that influence final biochar physical and chemical properties, total nutrient content, and perhaps more importantly tools one can use to predict biochar’s nutrient availability. Based on the large dataset collected, it appears that pyrolysis type (fast or slow) plays a minor role in biochar physico- (inorganic) chemical characteristics; few differences were evident between production styles. Pyrolysis temperature, however, affects biochar’s longevity, with pyrolysis temperatures > 500 °C generally leading to longer-term (i.e., > 1000 years) half-lives. Greater pyrolysis temperatures also led to biochars containing greater overall C and specific surface area (SSA), which could promote soil physico-chemical improvements. However, based on the collected data, it appears that feedstock selection has the largest influence on biochar properties. Specific surface area is greatest in wood-based biochars, which in combination with pyrolysis temperature could likely promote greater changes in soil physical characteristics over other feedstock-based biochars. Crop- and other grass-based biochars appear to have cation exchange capacities greater than other biochars, which in combination with pyrolysis temperature could potentially lead to longer-term changes in soil nutrient retention. The collected data also suggest that one can reasonably predict the availability of various biochar nutrients (e.g., N, P, K, Ca, Mg, Fe, and Cu) based on feedstock choice and total nutrient content. Results can be used to create designer biochars to help solve environmental issues and supply a variety of plant-available nutrients for crop growth.

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Feedstock choice, pyrolysis temperature and type influence biochar characteristics: a comprehensive meta-data analysis review

Agriculture is one of the sectors that strongly contribute to greenhouse gas emissions on the planet. In this sense, circular economy practices can be advantageous when using bioenergy in the agro-industrial sector. Although only about 9% of the world's economy is circular, global initiatives have acted to change that scenario. Unlike the linear economy (take-make-use-dispose), the circular economy (grow-make-use-restore) aims to influence material and energy flows to increase environmental gains and avoid costs. Based on that, this study aims to map bioenergy boosters through circular economy practices in agriculture. To that end, a systematic literature review was conducted to present what is being developed in this field. To identify the most relevant, high impact, studies in the area, the systematic literature review was performed in three databases, covering all available literature up to date. The main research themes, applications, research topics, area of activity, countries, journals, publisher, and history of publication were identified. Therewith, some trends and perspectives could be drawn. To date, no solidly established authors have been identified in the area. The theme is recent and the vast majority of documents have been published over the last four years. European countries have been pioneering and are the most prominent in terms of publications. The electricity generation and biofuel produced from biogas have shown representativeness and are sustainable opportunities to advance the theme. Therefore, this study can contribute to encouraging the agricultural sector in implementing or increasing the use of circular economy practices.

Mapping of research lines on circular economy practices in agriculture: From waste to energy

A critical review on performance indicators for evaluating soil biota and soil health of biochar-amended soils

Biochar is gaining significant attention due to its potential for carbon (C) sequestration, improvement of soil health, fertility enhancement, and crop productivity and quality. In this review, we discuss the most common available techniques for biochar production, the main physiochemical properties of biochar, and its effects on soil health, including physical, chemical, and biological parameters of soil quality and fertility, nutrient leaching, salt stress, and crop productivity and quality. In addition, the impacts of biochar addition on salt-affected and heavy metal contaminated soils were also reviewed. An ample body of literature supports the idea that soil amended with biochar has a high potential to increase crop productivity due to the concomitant improvement in soil structure, high nutrient use efficiency (NUE), aeration, porosity, and water-holding capacity (WHC), among other soil amendments. However, the increases in crop productivity in biochar-amended soils are most frequently reported in the coarse-textured and sandy soils compared with the fine-textured and fertile soils. Biochar has a significant effect on soil microbial community composition and abundance. The negative impacts that salt-affected and heavy metal polluted soils have on plant growth and yield and on components of soil quality such as soil aggregation and stability can be ameliorated by the application of biochar. Moreover, most of the positive impacts of biochar application have been observed when biochar was applied with other organic and inorganic amendments and fertilizers. Biochar addition to the soil can decrease the nitrogen (N) leaching and volatilization as well as increase NUE. However, some potential negative effects of biochar on microbial biomass and activity have been reported. There is also evidence that biochar addition can sorb and retain pesticides for long periods of time, which may result in a high weed infestation and control cost.

Biochar and Its Broad Impacts in Soil Quality and Fertility, Nutrient Leaching and Crop Productivity: A Review

Plant biomass is a highly abundant renewable resource that can be converted into several types of high-value-added products, including chemicals, biofuels and advanced materials. In the last few decades, an increasing number of biomass species and processing techniques have been developed to enhance the application of plant biomass followed by the industrial application of some of the products, during which varied technologies have been successfully developed. In this review, we summarize the different sources of plant biomass, the evolving technologies for treating it, and the various products derived from plant biomass. Moreover, the challenges inherent in the valorization of plant biomass used in high-value-added products are also discussed. Overall, with the increased use of plant biomass, the development of treatment technologies, and the solution of the challenges raised during plant biomass valorization, the value-added products derived from plant biomass will become greater in number and more valuable.

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Recent advances in the valorization of plant biomass

Restoration of soil quality using biochar and brown coal waste: A review.

Organic sorbents alter physicochemical soil properties and mitigate heavy metal (HM) bioavailability. However, some sorbents are labile and, therefore, introduce the risk of HM release into soil after mineralisation. Before field application, new stable organic sorbents such as woodchip biochar (BIO) and brown coal waste (BCW) need to be tested and compared with standard organic amendments like farmyard manure (FYM). An incubated pot experiment was conducted to investigate the efficacy of FYM, BIO and BCW (added to soil in pots at 5 and 10% w/w) to alter soil physicochemical properties and mitigate bioavailability of Cd, Pb and Zn spiked in treatments at different doses (in mg kg−1); 0 (not spiked), 1 (1 Cd, 70 Pb, 100 Zn) and 2 (3 Cd, 500 Pb, 700 Zn), and incubated for 9 weeks. At the end of the experiment, the EDTA-extractable HM fractions, pH, cation exchange capacity (CEC) and specific surface area (SSA, to check trends) were determined in all treated soils. Results showed that FYM, BCW and BIO generally improved all soil properties (except reduced pH from BCW and apparent SSA reduction from FYM) and accounted for respective maximum abatements of Cd (50.2, 69.9 and 25.5%), Pb (34.2, 64.3 and 17.4%) and Zn (14.9, 17.7 and 11.8%) bioavailability in soil. FYM and BCW were more effective at 10% w/w especially in the low contaminated soil, whereas the highest efficacy for BIO was at 5% w/w and in the high contaminated soil. The efficacies of sorption by the organic sorbents varied for different HMs and were in the orders: BCW > FYM > BIO for Cd, FYM > BCW > BIO for Pb and BIO > BCW > FYM for Zn. Soil pH and CEC were strongly correlated with HM bioavailability in all treatments and implied that immobilisation of HMs occurred via complex formation, ion exchange and pH-dependent specific adsorption. All three sorbents were beneficial as soil amendments, and in terms of HM mitigation, BCW had the highest efficacy, followed by FYM and then BIO. Considering the documented high soil stability of BCW and BIO, these results are promising for further trialling at field scale.

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Efficacy of Woodchip Biochar and Brown Coal Waste as Stable Sorbents for Abatement of Bioavailable Cadmium, Lead and Zinc in Soil

Organic amendments can improve soil quality which has knock-on environmental and agronomic benefits. However, the use of new and emerging organic amendments such as biochar and brown coal waste (BCW) in soil systems requires continuous holistic assessments for robust consensus building in their environmental and agricultural applications. To examine the application of BCW and woodchip biochar (BIO) in agroecosystems, secondary data from literature on environmental (soil, air and water) aspects were compiled with primary agronomic data from a 3-year multicropping field trial and collated with supplementary data on economic factors (e.g. cost and availability). For the field trial, replicated plots were amended with FYM (for comparative reasons), BCW and BIO at 30, 24.2 and 12.8 for t ha–1, respectively, with and without NPK and cultivated in a cropping sequence of maize, potato and barley. At the end of each season, soils were characterised for pH, cation exchange capacity (CEC) and fertility (macronutrient contents) in addition to nutrient uptake, nutritional quality and yield of crops. Compared with FYM, biochar and BCW were found to be associated with greater improvements in soil quality (e.g. building of soil structure and C sequestration) and knock-on water and air quality benefits mainly facilitated via increased cation retention and humic-linked sorption which abated gaseous emission and mitigated nutrient and heavy metal leaching. These along with variable improvements in soil chemistry, fertility and nutrient uptake in the agronomic field trial accounted for increased mean crop yield across treatments (higher with NPK): FYM (32.7 and 71.7%), BCW (33.5 and 60.1%) and BIO (21.8 and 48.2%). Additionally, biochar and BCW have lower pollutant (e.g. heavy metals) contents and were found to provide additional sustainability and net abatement cost-benefits. While the agronomic benefits of biochar and BCW were slightly lower compared with that of FYM, their lower environmental footprints and associated sustainability benefits are clear advantages for their adoption in environmental and agricultural applications.

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Holistic Assessment of Biochar and Brown Coal Waste as Organic Amendments in Sustainable Environmental and Agricultural Applications

Humic acids (HAs) regulate soil chemical reactivity and improve many soil functions. The amendment of soil with organic materials increases soil organic matter (SOM) content and promotes the formation of HAs. However, the effect of the type, frequency and duration of amendment, and pedoclimatic conditions on SOM transformation and HA structural changes remains unclear. Herein, four experimental field sites (S1–4) with short-to-long-term organic fertilisation schemes were used to assess the effects of such factors, i.e., S1: loamy sand amended once with farmyard manure (FYM), brown coal waste (BCW), and biochar (BIO) for 0.5 and 1.5 years; S2: silt loam amended once with BIO for 8 years; S3: loamy sand amended every 5 years with FYM for 94 years; and S4: clayey silt amended every 2 years with FYM for 116 years. All HAs were extracted and analysed for structural differences by elemental analysis (EA), attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR), solid-state cross polarisation magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS 13C-NMR), and differential scanning calorimetry (DSC). Results from EA, FTIR, and NMR showed that the long-term samples from S3 (treatments, T9–T10) and S4 (T11–T12) had the greatest aromatic characteristics, which increased with FYM amendment (T10 and T12). These agreed with DSC data, which indicated lower aliphatic contents compared with other samples. Samples from S2 (T7–T8), with receded amendment effects, had less aromatic and greater aliphatic characteristics compared with the short-term samples, S1 (T1–T6). In S1, structural changes were limited, but aromaticity increased with BIO (T3 and T6) compared with corresponding FYM (T1 and T4) and BCW (T2 and T5) amendments due to inherently high aromatic groups in the former. Overall, the results showed that the site (due to differences in pedoclimatic conditions), field age of OM, and amendment frequency were the main factors that influenced HA structure, and hence SOM transformation. Regular, long-term organic amendment increases the aromatic characteristics of HAs, which can improve soil functionality, but short-term structural improvements are achievable only when amending material is rich in aromatic compounds.

https://www.mdpi.com/2073-4395/12/2/283/pdf?version=1643072588

Collins Amoah-Antwi

Papers

Restoration of soil quality using biochar and brown coal waste: A review.

Efficacy of Woodchip Biochar and Brown Coal Waste as Stable Sorbents for Abatement of Bioavailable Cadmium, Lead and Zinc in Soil

Holistic Assessment of Biochar and Brown Coal Waste as Organic Amendments in Sustainable Environmental and Agricultural Applications

Assessing Factors Controlling Structural Changes of Humic Acids in Soils Amended with Organic Materials to Improve Soil Functionality