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1. Impact of biochar amendment on soil microbial biomass carbon enhancement under field experiments: a meta-analysis

   https://doi.org/10.1007/s42773-024-00391-6  

   Kumar, Yogesh; Ren, Wei; Tao, Haiying; Tao, Bo; Lindsey, Laura_E (January 2025, Biochar)

   Abstract Biochar is well-accepted as a viable climate mitigation strategy to promote agricultural and environmental benefits such as soil carbon sequestration and crop productivity while reducing greenhouse gas emissions. However, its effects on soil microbial biomass carbon (SMBC) in field experiments have not yet been thoroughly explored. In this study, we collected 539 paired globally published observations to study the impacts of biochar on SMBC under field experiments. Our results suggested an overall positive impact of biochar (21.31%) on SMBC, varying widely with different climate conditions, soil types, biochar properties, and management practices. Biochar application exhibits significant impacts under climates with mean annual temperature (MAT) < 15 °C and mean annual precipitation (MAP) between 500 and 1000 mm. Soils of coarse and fine texture, alkaline pH (SPH), soil total organic carbon (STC) content up to 10 g/kg, soil total nitrogen (STN) content up to 1.5 g/kg, and low soil cation exchange capacity (SCEC) content of < 5 cmol/kg received higher positive effects of biochar application on SMBC. Biochar produced from crop residue, specifically from cotton and maize residue, at pyrolysis temperature (BTM) of < 400 °C, with a pH (BPH) between 8 and 9, low application rate (BAP) of < 10 t/ha, and high ash content (BASH) > 400 g/kg resulted in an increase in SMBC. Low biochar total carbon (BTC) and high total nitrogen (BTN) positively affect the SMBC. Repeated application significantly increased the SMBC by 50.11%, and fresh biochar in the soil (≤ 6 months) enhanced SMBC compared to the single application and aged biochar. Biochar applied with nitrogen fertilizer (up to 300 kg/ha) and manure/compost showed significant improvements in SMBC, but co-application with straw resulted in a slight negative impact on the SMBC. The best-fit gradient boosting machines model, which had the lowest root mean square error, demonstrated the relative importance of various factors on biochar effectiveness: biochar, soil, climate, and nitrogen applications at 46.2%, 38.1%, 8.3%, and 7.4%, respectively. Soil clay proportion, BAP, nitrogen application, and MAT were the most critical variables for biochar impacts on SMBC. The results showed that biochar efficiency varies significantly in different climatic conditions, soil environments, field management practices, biochar properties, and feedstock types. Our meta-analysis of field experiments provides the first quantitative review of biochar impacts on SMBC, demonstrating its potential for rehabilitating nutrient-deprived soils and promoting sustainable land management. To improve the efficiency of biochar amendment, we call for long-term field experiments to measure SMBC across diverse agroecosystems. Graphical Abstract 

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2. Comparing Physicochemical Properties and Sorption Behaviors of Pyrolysis-Derived and Microwave-Mediated Biochar

   https://doi.org/10.3390/su13042359  

   Brickler, Colten A.; Wu, Yudi; Li, Simeng; Anandhi, Aavudai; Chen, Gang (February 2021, Sustainability)

   null (Ed.)

   Biochar’s ability to amend and remediate agricultural soil has been a growing interest, though the energy expenses from high-temperature pyrolysis deter the product’s use. Therefore, it is urgent to improve the pyrolysis efficiency while ensuring the quality of produced biochar. The present study utilized three types of feedstock (i.e., switchgrass, biosolid, and water oak leaves) to produce biochar via conventional slow pyrolysis and microwave pyrolysis at different temperature/energy input. The produced biochar was characterized and comprehensively compared in terms of their physiochemical properties (e.g., surface functionality, elemental composition, and thermal stability). It was discovered that microwave-mediated biochar was more resistant to thermal decomposition, indicated by a higher production yield, yet more diverse surface functional groups were preserved than slow pyrolysis-derived biochar. A nutrient (NO3-N) adsorption isotherm study displayed that microwave-mediated biochar exhibited greater adsorption (13.3 mg g−1) than that of slow pyrolysis-derived biochar (3.1 mg g−1), proving its potential for future applications. Results suggested that microwaves pyrolysis is a promising method for biochar production. 

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3. Perennial grass bioenergy cropping systems: Impacts on soil fauna and implications for soil carbon accrual

   https://doi.org/10.1111/gcbb.12903  

   Zahorec, Allison; Reid, Matthew L.; Tiemann, Lisa K.; Landis, Douglas A. (October 2021, GCB Bioenergy)

   ABSTRACT Perennial grass energy crop production is necessary for the successful and sustainable expansion of bioenergy in North America. Numerous environmental advantages are associated with perennial grass cropping systems, including their potential to promote soil carbon accrual. Despite growing research interest in the abiotic and biotic factors driving soil carbon cycling within perennial grass cropping systems, soil fauna remain a critical yet largely unexplored component of these ecosystems. By regulating microbial activity and organic matter decomposition dynamics, soil fauna influence soil carbon stability with potentially significant implications for soil carbon accrual. We begin by reviewing the diverse, predominantly indirect effects of soil fauna on soil carbon dynamics in the context of perennial grass cropping systems. Since the impacts of perennial grass energy crop production on soil fauna will mediate their potential contributions to soil carbon accrual, we then discuss how perennial grass energy crop traits, diversity, and management influence soil fauna community structure and activity. We assert that continued research into the interactions of soil fauna, microbes, and organic matter will be important for advancing our understanding of soil carbon dynamics in perennial grass cropping systems. Furthermore, explicit consideration of soil faunal effects on soil carbon can improve our ability to predict changes in soil carbon following perennial grass cropping system establishment. We conclude by addressing the major knowledge gaps that should be prioritized to better understand and model the complex connections between perennial grass bioenergy systems, soil fauna, and carbon accrual. 

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4. The Role of Biochar in Regulating the Carbon, Phosphorus, and Nitrogen Cycles Exemplified by Soil Systems

   https://doi.org/10.3390/su13105612  

   Pan, Shu-Yuan; Dong, Cheng-Di; Su, Jenn-Fang; Wang, Po-Yen; Chen, Chiu-Wen; Chang, Jo-Shu; Kim, Hyunook; Huang, Chin-Pao; Hung, Chang-Mao (May 2021, Sustainability)

   null (Ed.)

   Biochar is a carbon-rich material prepared from the pyrolysis of biomass under various conditions. Recently, biochar drew great attention due to its promising potential in climate change mitigation, soil amendment, and environmental control. Obviously, biochar can be a beneficial soil amendment in several ways including preventing nutrients loss due to leaching, increasing N and P mineralization, and enabling the microbial mediation of N2O and CO2 emissions. However, there are also conflicting reports on biochar effects, such as water logging and weathering induced change of surface properties that ultimately affects microbial growth and soil fertility. Despite the voluminous reports on soil and biochar properties, few studies have systematically addressed the effects of biochar on the sequestration of carbon, nitrogen, and phosphorus in soils. Information on microbially-mediated transformation of carbon (C), nitrogen (N), and phosphorus (P) species in the soil environment remains relatively uncertain. A systematic documentation of how biochar influences the fate and transport of carbon, phosphorus, and nitrogen in soil is crucial to promoting biochar applications toward environmental sustainability. This report first provides an overview on the adsorption of carbon, phosphorus, and nitrogen species on biochar, particularly in soil systems. Then, the biochar-mediated transformation of organic species, and the transport of carbon, nitrogen, and phosphorus in soil systems are discussed. This review also reports on the weathering process of biochar and implications in the soil environment. Lastly, the current knowledge gaps and priority research directions for the biochar-amended systems in the future are assessed. This review focuses on literatures published in the past decade (2009–2021) on the adsorption, degradation, transport, weathering, and transformation of C, N, and P species in soil systems with respect to biochar applications. 

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5. On the Effect of Biochar Application on the Hydraulic Properties of Salt-affected Green Stormwater Infrastructure

   Finnegan, Maxwell; Khatei, Ganesh; Rinaldo, Tobia; Caplan, Joshua; Van_Pelt, Scott; D'Odorico, Paolo; Ravi, Sujith (December 2024, American Geophysical Union)

   Soil salinization is an increasing global problem, especially in agricultural, coastal, and roadside environments. The increasing intensity of precipitation events due to climate change may be exacerbating these effects, such as through larger pulses of deicing salts entering roadside green stormwater infrastructure (GSI) and stronger coastal storms bringing seawater further inland. Although soils are often amended with biochar to remove pollutants and improve hydraulic properties, it may also mitigate the impact of salinity. Here, we compared the water retention properties and unsaturated hydraulic conductivities of both biochar-amended and unamended GSI soil media with varying salinity levels (1-25 dS m-1, using Na+ salts). The effects of salinity on both matric and osmotic potential included shifts in the plant-available water range, with the magnitude depending on the salt concentration and biochar content. Overall, biochar addition decreased the salinity and improved plant water availability in salt-affected soils. There was an increase in the integral water capacity (which describes the total amount of water the soil media can hold and release to a plant) for biochar-amended saline soils, demonstrating that biochar can reduce the total osmo-matric stress. On a macro scale, the high density of pores in biochar appears to increase soil hydraulic conductivity while reducing osmotic potential by adsorbing salt ions. On a micro scale, the negative surface charge of biochar likely counteracts the impact of the electric double layer of saline soils, reducing the total osmo-matric force on water molecules in soil solution. In effect, this helps the plant's osmotic potential to overcome the forces holding water molecules to soil grains. As soils become more saline due to ongoing climate-related snow events, biochar application might be an effective management technique for roadside and other saline soils. 

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