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Bioengineered structures, such as landfill cover, vegetated slopes or embankments, green roof and turf are comprised of soil and vegetation where vegetation imparts stability and protection through root reinforcement and hydrologic action. Soil in bioengineered structures often compacted and subjected to prolong drying due to irregular irrigation which necessitates the investigation of soil properties and vegetation growth in biochar-amended soil (BAS) under large suction range and it is scarce in the literature. In the present study, the effect of different biochar types on soil properties, and the vegetation growth in compacted soil and under large suction range was investigated for application in bioengineered structures. The results revealed that the biochar amendment decreased the dry density (5–32%) and increased the water retention capacity (θs by 15–104%, θ1500 by 82–445% and plant available water content (PAWC) by 22–55%), pH (28–77%) and cation exchange capacity (CEC, 16–723%) of the soil. Further, the vegetation growth i.e., vegetation density, dry root mass and shoot mass increased by 8–13%, 33–108% and 4–157% respectively after biochar amendment. The vegetation wilting was started at a higher suction (~ 900 kPa) relative to bare soil (800 kPa), the permanent wilting point (PWP) increased (by 3–35%) and the complete photosynthetic activity remained unchanged at a higher suction (1600 kPa) relative to bare soil (1050 kPa) after biochar amendment. Among the biochar types i.e., Sugarcane Bagasse biochar (SBB), Mesquite biochar (MB) and Water Hyacinth biochar (WHB) tested, the MB showed the best performance i.e., the suitable vegetation growth and health status. The improved water retention due to increased porosity, specific surface area (SSA) and presence of hydrophilic functional groups, and the higher pH, CEC and lower dry density in BAS attributed to the higher vegetation growth. The findings of the present study suggest the application of BAS in bioengineered structures. [ABSTRACT FROM AUTHOR]

Biochar is a carbon-rich material produced mainly from plant- and animal-based biomass through thermochemical conversion. It is often amended to soil for methane oxidation in landfill cover soil and for improving crop growth and yield by enhancing soil fertility. The application of biochar for removing organic and inorganic pollutants from soil and water is also well established. Biochar could be of potential use as an engineering material for enhancing the stability and performance of bioengineered structures that mainly consist of soil and vegetation. Bioengineered structures are commonly adopted in many parts of the world due to their multiple beneficial features. The stability and performance of these structures depend on the soil engineering properties and vegetation performance. However, the performance of vegetation is interrelated with the soil engineering properties. Therefore, the effects of biochar on soil engineering properties and vegetation performance, i.e., the soil-biochar-plant interaction, need to be studied and summarized. In the present study, the effect of biochar on the soil engineering properties and vegetation performance was reviewed. The review of the literature revealed that the amendment of biochar affects the soil engineering properties and vegetation performance by altering mainly soil pore system and fertility. However, this depends on many factors, such as soil type, biochar type, pyrolysis temperature, particle size of biochar, biochar amendment rate, aging of biochar, and the type of vegetation grown. Furthermore, the reviewed or existing literatures are mostly for agricultural soil, which is different from the soil state in bioengineered structures in terms of compaction density, suction range, and design life or duration. In addition, the properties of biochar are highly variable with its production process. Hence, the factors of soil state in bioengineered structures and the optimized production process of biochar need to be considered for maximizing the long-term performance of bioengineered structures. [ABSTRACT FROM AUTHOR]

Highlights • Stomatal conductance and surface area characteristic curves were proposed. • Stomatal conductance was found to be almost nil at 2431 kPa (i.e., wilting point). • Grass surface varied drastically with increase in suction from 138 kPa to 3642 kPa. Abstract Evapotranspiration was determined to be hydrological effect which induces suction. Evapotranspiration induced suction governs the slope stability, ground water recharge and runoff. This study focuses on suction induced in root zone of mix grass used in green infrastructure. Most of the previous studies focused on evapotranspiration induced suction less than 100 kPa measured using tensiometers. However, for investigating the drought condition, it is essential to obtain suction data greater than 100 kPa. It was noted that the response of plant parameters such as stomatal conductance and surface area were not considered holistically evapotranspiration induced suction. The main objective of this study is to investigate relationship among evapotranspiration induced suction, stomatal conductance and surface area for a mix grass species used in green infrastructure subjected to drought stress (corresponds to suction > 100 kPa). Stomatal conductance was observed to increase up to suction (6 ± 1 kPa) corresponding to volumetric field capacity. Thereafter, large decrease (more than 90%) in stomatal conductance was found with an increase in suction. Stomatal conductance was found to be 0 at 2431 kPa (i.e., wilting point). Change in normalized surface areas of mix grass was found to be relatively low (within ±15%) with an increase in suction up to 138 kPa. However, beyond 138 kPa, it varied drastically (by 31–68%) with an increase in suction from 138 kPa to 3642 kPa. Two new relationships i.e., Stomatal conductance characteristic curve (SCCC) and surface area characteristic curve (SACC) were proposed. Therefore, the relationships developed in current study help to analyze the performance of green infrastructure accurately. [ABSTRACT FROM AUTHOR]

Soil in embankments is often amended with several additives for supporting the vegetation growth on the side slopes. Biochar, a stable, nutrient loaded and moisture retentive material, could be amended to the embankment soils. The positive impacts of biochar on soil properties, soil water and nutrient retention, microbial activity and growth of crops are well established. However, the load-bearing capacity of biochar-amended soil which is utmost important for a material to be used in embankment is rarely reported in literature. The present study aims to investigate the shear strength and load-bearing capacity of biochar-amended soil for application in embankments. For assessing the shear strength and load-bearing capacity, California bearing ratio (CBR) and direct shear tests were conducted on bare and 5%, 10% and 15% (w /w) biochar-amended silty sand and pure sand. The results revealed that the biochar amendment decreased the dry unit weight (6–19%), and increased the shear strength (cohesion (c) and angle of internal friction (ϕ)) and load-bearing capacity of both the soils by 22–228% and 17–89% respectively. Further, the biochar amendment improved the vegetation root (34–108%) and shoot (29–157%) mass, ensuring the enhanced stability and protection (erosion). Thus, the results suggest the application of biochar-amended soil in embankments, however future field-scale trials are needed before application. [ABSTRACT FROM AUTHOR]

• Biochar affects the unsaturated hydraulic conductivity (K unsat) of compacted soils. • Biochar amendment improved the water retention capacity of the compacted soils. • The K unsat of soils is found to be decreased significantly after biochar amendment. • Biochar-amended soil could promote vegetation growth in bioengineered structures. This study investigates the influence of biochar amendment on the water retention and unsaturated hydraulic conductivity (K unsat) of compacted soils focusing on its potential application in bioengineered structures. Physical properties, water retention characteristics and K unsat of two different soils, such as silty sand and pure sand and amended with 5% and 10% (w/w) biochar made from mesquite were measured with the help of instantaneous profile method (IPM). The water retention capacity of the biochar-amended soil was characterised by plotting soil water retention curve (SWRC) and estimating the saturated volumetric water content (θ s), residual water content (θ r), shape parameter ' n ' and plant available water content (PAWC). The results revealed that the amendment of biochar in the soils increased the θ s (by 20–30%), θ r (60–370%) and PAWC (7–60%), and decreased the n (by 5–18%) and K unsat (one-two order). The microstructural observation showed that the hydrophilic surface functional groups and intra-pores in biochar contributed to the improved water retention, while the altered pore size distribution and porosity of the soils due to biochar amendment increased the tortuosity of the water flow path and hence reduced the K unsat. Based on the findings, biochar-amended soil is proposed to be used in bioengineered structures that could promote the growth of vegetation and improve the performance. [ABSTRACT FROM AUTHOR]

• Effect of biochar on the hydro-physical properties of compacted soils is presented. • The biochar made from the hardwood of mesquite is used in this study. • Biochar decreased specific gravity, dry density and plasticity index of the soils. • Impact of biochar on saturated hydraulic conductivity is found to be soil dependent. • Impact of biochar on infiltration rate is unique and independent of soil type considered. Biochar is a carbon-rich porous material obtained after pyrolysis of labile biomass in oxygen deficit condition. The production of biochar from invasive weed mesquite biomass could be beneficial of managing waste and preventing the emission of CO 2 gas by open combustion, and amending them in soil could sequester carbon in soil and improve soil properties. The effect of biochar on soil hydraulic properties was studied for loose soils suitable for agriculture. However, soils in engineered/bioengineered structures often compacted for achieving structural stability. Moreover, biochar of different feedstock poses variable effect on soil hydro-physical properties and a combined study of hydro-physical properties of soil amended with mesquite biochar lacks in the existing literature. In the present study, the effect of mesquite biochar on the hydro-physical properties, such as Atterberg limits, compaction characteristics, infiltration rate (I) and saturated hydraulic conductivity (K sat) of compacted silty sand and pure sand is investigated for potential application in bioengineered structures. The results show that the amendment of 5%, 10% and 15% biochar increased the atterberg limits and water absorption capacity while decreased the plasticity index, specific gravity, dry density and I of the soils. Moreover, the K sat is found to be increased in silty sand whereas decreased in pure sand due to biochar amended. These changes in soil properties are attributed to the altered physical properties, mainly porosity (inter-pores) of the soil by the biochar amendment and the presence of chemical compound in biochar surface. The reduced I and K sat in the present study suggest application of biochar amended soil in bioengineered structures; however, further field-scale studies are needed before implication. [ABSTRACT FROM AUTHOR]

• A detailed review of soil water retention characteristics (SWRC) of biochar-amended soil is presented. • Biochar feedstock type, pyrolysis temperature, particle size and aging has a strong influence on the SWRC. • The SWRC of biochar-amended soil also depends on soil type and corresponding compaction condition. • Correlations among SWRC parameters and biochar properties were developed and presented. • Such a study will be quite handy while applying biochar-amended soil in geotechnical and agricultural applications. Biochar is a stable carbon-rich product obtained through pyrolysis of plant and animal-based biomass. Soil is often amended with biochar due to the beneficial features, such as carbon sequestration, improvement of crop growth and yield by enhancing soil fertility, removal of an organic and inorganic pollutant from the soil, and improvement of water retention properties of the soil. Fundamentally, the amendment of soil with biochar alters the soil water retention characteristics (SWRC) of the soil. This is primarily due to the inherent properties of biochar that includes large specific surface area (SSA) by the intra-particle pores, and the functional groups present in biochar surface. SWRC is vital for both agricultural soil and soil in geotechnical or geo-environmental engineering structures due to the presence of vegetation. The effect of biochar on the SWRC of agricultural soil was extensively studied. However, it is rarely studied for soil in geotechnical or geo-environmental engineering structures, such as landfill cover, bioengineered slope, embankment, green roof, etc. Soil in these structures subjects to a distinct condition, in terms of compaction state and design life compared to agricultural soil. Therefore, a comprehensive gathering of information on the effect of biochar on the SWRC and the factors controlling the biochar influence is needed for potential investigation and application of biochar amendment for soil in geotechnical or geo-environmental engineering structures. In this article, the effect of biochar amendment on the SWRC of soil has been reviewed and summarized by considering various factors controlling the influence of biochar on the SWRC. The literature review revealed that the amendment of soil with biochar could improve the SWRC while few occasions not influence the SWRC. Factors, such as feedstock type and pyrolysis temperature, particle size of biochar, soil type, and compaction state have strong bearing on the influence of biochar on the SWRC. [ABSTRACT FROM AUTHOR]

Summary: This study has dealt with the synthesis and characterization of biochars produced from three biomasses, viz. water hyacinth (whole plant and its components), yellow oleander, and sugarcane bagasse, and their comparative assessment for potential application in agronomy and energy production. The pyrolysis was carried out in a fixed batch reactor at 350°C and 550°C with a heating rate of 20°Cmin−1. Biochars were characterized for proximate and ultimate (elemental) analysis, and also using standard techniques (SEM, EDX, TGA, BET, XRD, and FTIR). Biochars produced at 550°C from all the feedstock had good properties (carbon content: 39.09‐80.74%, pH: 7.36‐10.42, calorific value: 16.98‐30.18 MJ kg−1, and ash content: 0.89%‐21.78%). Moreover, relatively low atomic ratios (H/C 0.25‐0.47 and O/C 0.15‐1.11) of all biochars indicated their potential as solid fuel. XRD results showed the presence of amorphous and crystalline structures, and minerals like sylivite, quartz, kalsilite, and tridymite in the biochar. Biochar produced from sugarcane bagasse at 550°C possessed the best properties: fixed carbon (77.42%), bulk density (0.13 kg/m3), brunauer–emmett–teller (BET) surface area (17.78 m2/g), pore size (12.86 nm), total pore volume (0.025 cm3/g), calorific value (30.18 MJ kg−1), ash content (1.16%), and moisture content (2.03%). [ABSTRACT FROM AUTHOR]