Biochar-amended Soils Research Articles

Responses of soil microbial communities to manure and biochar in wheat cultivation of a rice-wheat rotation agroecosystem in East China

Soil contamination in agroecosystems remains an environmental problem of global concern. Biochar has been suggested as an organic amendment to alleviate soil pollution, sequester carbon, and improve fertility. Yet, information is still lacking on how bacterial and fungal communities in acidic bulk and rhizosphere soils respond to swine manure and its biochar. In this study, biochar and swine manure were applied at two rates of 1.5 and 3 t ha-1 in a rice-wheat rotation field study to assess how soil characteristics, especially pH and the availability of chemical elements, correlate to compositional variations of bacteria and fungi in bulk and rhizosphere soils. Our results showed that biochar and manure amendments at higher rates promoted bacterial richness index in bulk and rhizosphere soils through increasing soil pH and reducing As and Cu availability. For beta diversity, compared with As and Cu availability, soil pH had opposite effects on both bacterial and fungal communities. Specifically, biochar and swine manure application stimulated bacterial class of Gemmatimonadetes, Deltaproteobacteria, and Gammaproteobacteria via increasing pH and decreasing available chemical elements. Opposite trends of fungal community responding to biochar and manure was found. For example, biochar restrained the fungal class of Eurotiomycetes via decreasing As and Cu, but manure inhibited Leotiomycetes mainly due to an increase in soil pH and a decrease in soil dissolved organic C (DOC). These evidences suggest that both bacterial and fungal communities respond significantly to biochar and manure amendments in both bulk and rhizosphere soils, possibly due to their sensitive adaptation to soil environmental variations, such as pH levels and availability of chemical elements.

Modelling and spectroscopic investigation of 2,4-D adsorption in soil amended with pine sawdust, paunch grass and sewage sludge biochars

2,4-Dichlorophenoxyacetic acid (2,4-D) is a widely used herbicide possessing high herbicidal activity; however, it is potentially toxic to humans and quite persistent in the environment. We investigated the adsorption of 2,4-D in two pasture soils amended with pine sawdust (PSD), paunch grass (PG) and sewage sludge (SS) biochars using batch studies. The results showed that PSD biochar produced at 700 oC exhibited the highest adsorption capacity for 2,4-D among the waste-derived biochars tested, which is 200-fold greater than the control and other biochar-amended soils. In general, the sorption affinity of 2,4-D for biochar amended soils followed an order: PSD > > PG > SS. The high adsorption capacity of the PSD may be attributed to its significantly higher specific surface area of 795 m2·g-1 as compared to other soils and biochars. Moreover, the results of the physicochemical characterization showed no difference in surface oxygen functional groups among the PSD, PG and SS. These findings indicate that oxygen-containing surface functional groups have a negligible role in 2,4-D adsorption, as evident from the spectroscopic investigation, thus emphasizing the role of surface area in the 2,4-D adsorption. Lastly, pore intrusion/filling, hydrogen bonding and π-π EDA interactions are postulated to be the plausible adsorption mechanisms for 2,4-D onto biochar amended soils.

Effects of Biochar Soil Amendment on the Rooting and Early Growth of African Mahogany Species: Khaya Ivorensis And Khaya Grandifoliola

Biochar application as growing medium is being recognized globally in forest and crop restoration. Biochar soil amendment was proposed to improve rooting media characteristics for effective rooting of mahogany stem cuttings in vegetative propagation system.

Transmissible Effects of a Biochar Amendment to an Upper Soil Zone Upon an Associated Lower Zone, Including Attenuation of Soybean Cyst Nematode (Heterodera glycines)

Mung bean residues stimulate the hatching of soybean cyst nematode (SCN). In our previous study, combined incorporation of mung bean residues and biochar into soil can be effective in suppression of the soybean cyst nematode (SCN), Heterodera glycines, in the upper layer soil. However, there are no data available as to whether such effects are transmissible, and could for example be manifest in subsoil zones where such incorporation is confined to topsoils, via water-based pathways. We evaluated the effects of leachate passage from a biochar-amended soil in an upper soil zone to a lower zone in a microcosm-based system, upon a range of physicochemical properties and density of SCN. Disturbed soil was filled in a total of 9 cylindrical cores with two layers. The upper layer (0–15 cm) was amended with biochar at rates equivalent to 0, 0.3% or 1.8%, with bulk density set at of 1.1 g cm−3. The lower layer (15–25 cm) without biochar amendment was compacted to 1.2 g cm−3. Mung beans were grown for two weeks and incorporated into the upper layer. Water was surface-applied to the cores 4, 6, and 8 weeks after mung bean incorporation. After 16 weeks, the upper and lower layer soils were separately collected and assayed. The presence of biochar in the upper layer reduced the abundance of free-living nematodes, mainly bacterivorous, but increased that of a predator genus Ecumenicus in this zone. In the lower layer of soil under a biochar-amended upper layer, available P and soluble cations were increased as were abundances of total nematodes including Ecumenicus, resulting in greater maturity index, basal and structure indices. Notably, SCN density was decreased in lower zones by more than 90% compared to zero-biochar controls. This demonstrates that the effects of biochar upon soil properties, including impacts on biota and plant pathogens, are transmissible.

Chemical properties of soil determine the persistence and bioavailability of polycyclic aromatic hydrocarbons in sewage sludge- or sewage sludge/biomass-derived biochar-amended soils

In this study the persistence (organic solvent extractable) and bioavailability (freely dissolved) of polycyclic aromatic hydrocarbons (PAHs) in soils with various properties amended with sewage sludge (BCSSL)- or sewage sludge/biomass (BCSSLW)-derived biochars was examined. Biochars produced at 600 °C were applied to soils (acidic, neutral, or alkaline) at a dose of 2% and subsequently incubated for 180 days. Here, the use of biochars regarding the soil's type was examined for the first time. Depending on the soil pH and the feedstock, the content of sum of 16 organic solvent extractable PAHs was found to decrease from 7.5 to 37% (soil + BCSSL) and from 24 to 40% (soil + BCSSLW). The decrease in the content of sum of 16 freely dissolved PAHs ranged from 18 to 36% (soil + BCSSL) and from 17 to 54% (soil + BCSSLW). In acidic BCSSL-amended soil and the alkaline BCSSLW-amended soil no statistically significant differences in the content of sum of 16 freely dissolved PAHs were noted between the beginning and end of the study. BCSSLW was characterized by a greater reduction content of organic solvent extractable PAHs in the acidic and alkaline soils, while in the neutral one – BCSSL. In turn, a larger reduction in freely dissolved PAH content in the acidic and neutral soils could be seen in the presence of BCSSLW, whereas in the alkaline soil in the presence of BCSSL. The persistence and bioavailability of PAHs in the biochar-amended soils were closely related to the chemical properties of these soils. This was confirmed by numerous statistically significant (P ≤ 0.05) relationships between organic solvent extractable PAHs and pH, cation exchange capacity, available magnesium, potassium and phosphorus, and dissolved organic carbon as well as between freely dissolved PAH and pH, dissolved organic carbon, available potassium and phosphorus content, and electrical conductivity.

Typical Sulfonamide Antibiotics Removal by Biochar-Amended River Coarse Sand during Groundwater Recharge.

The high porosity of medium-coarse sand (MCS) layers in groundwater recharge areas presents a high environmental risk. Sulfamethoxazole (SMX) and trimethoprim (TMP) are two common sulfonamide antibiotics in surface water that have a high propensity to migrate into groundwater. In this study, four biochars were prepared and biochar-amended soil aquifer treatment (SAT) columns were constructed to remove SMX and TMP. Batch experiments demonstrated that the sorption isotherms conformed to the Freundlich model. The maximum adsorptions of biochars prepared at 700 °C were 54.73 and 67.62 mg/g for SMX and 59.3 and 73.38 mg/g for TMP. Electrostatic interaction may be one of the primary mechanisms of adsorption. The column experiments showed that the SMX and TMP removal rate of the biochar-amended SAT was as high as 96%, while that of the MCS SAT was less than 5%. The addition of biochar greatly improved the retention capacity of the pollutants in the MCS layer in the groundwater recharge area and effectively reduced environmental risk.

Investigating soil properties and vegetation parameters in different biochar-amended vegetated soil at large suction for application in bioengineered structures

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 (~ 900kPa) relative to bare soil (800kPa), the permanent wilting point (PWP) increased (by 3-35%) and the complete photosynthetic activity remained unchanged at a higher suction (1600kPa) relative to bare soil (1050kPa) 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.

Self-functionalization of soil-aged biochar surfaces increases nitrate retention

Nutrient retention in biochar amended soil has yielded variable results, with poorly understood mechanisms. Identification of changes on biochar surfaces during in situ soil aging can provide mechanistic information on the role of biochar on nutrient retention. In the current greenhouse study, we analyzed changes of biochar surface characteristics from aging in two soils with different iron levels and amended with two types of manure under corn. On pristine biochar surfaces, we detected no iron species. In contrast, after soil aging (70 days), a self-functionalization of biochar surfaces with iron oxides was observed, which can be explained by soil redox cycles allowing reduced iron(II) to migrate on biochar surfaces followed by its re-oxidation. This self-functionalization is proposed as an underlying mechanism explaining the significantly (p < 0.01) increased nitrate retention by 29–180 % in biochar amended soil. Significant (p < 0.05) reductions in leachate phosphate (18–41 %) and dissolved organic carbon (8.8–55 %) were also observed after biochar surface functionalization. Our results indicate that redox-driven iron oxide formation on surfaces of biochar in the soil can be a critical process explaining the dynamic nature of nutrient retention observed in biochar amended soils. Identifying soil environmental conditions most beneficial for such surface functionalization, which has the potential to increase nutrient retention, is critical for implementing efficient biochar amendment strategies and for increased resource efficiency in agroecosystems.

The effect of biochar on mycorrhizal fungi mediated nutrient uptake by coconut (Cocos nucifera L.) seedlings grown on a Sandy Regosol

Biochar amendment of soil may ameliorate inherently infertile soils, such as in the typical coconut (Cocos nucifera L.) growth areas along tropical coasts, where, moreover, temporary moisture stress commonly occurs. We conducted a pot experiment to evaluate the effects of biochar soil amendment (1% w/w) produced from Gliricidia sepium stems (BC-Gly) and rice husks (BC-RiH) on the growth of coconut seedlings and on N and P uptake mediated by mycorrhizae under wet or dry conditions in a Sandy Regosol. The pots were divided into root and hyphal zones by a nylon mesh, where 15N labelled N and P nutrients were only provided in the hyphal zone. Under wet conditions, biochar application did not affect plant growth, while under dry conditions, the BC-Gly increased root and plant growth similar to that under wet conditions. BC-Gly increased the acidic pH of the soil to a neutral level, and the microbial community shifted towards a higher fungal abundance. The P accumulated (Pacc) in roots was higher with BC-Gly and BC-RiH under dry and wet conditions, respectively. Pacc weakly correlated with the abundance of arbuscular mycorrhizal fungi (AMF) in the hyphal zone. With BC-Gly roots showed lower N derived from fertilizer. We conclude that biochar application has no impact on crop growth under wet conditions, while under dry conditions, BC-Gly stimulates crop growth and P uptake, probably through liming induced P availability but also possibly by some enhancement of AMF growth. The shift in the fungal-oriented microbial community and reduced plant fertilizer N uptake suggested that BC-Gly acted as an additional N source.Graphical

Effects of Wood-Derived Biochar on Germination, Physiology, and Growth of European Beech (Fagus sylvatica L.) and Turkey Oak (Quercus cerris L.)

Biochar (BC) soil amendments could partially counteract soil carbon (C) stock decrease in broad-leaved forests in Italy; however, its effects on the growth of representative tree species—Fagus sylvatica L. and Quercus cerris L.—has not yet been addressed. We examine whether seed germination and growth of these species are affected by addition of BC obtained from deciduous broadleaf trees. Seeds were left to germinate in greenhouse conditions under three different BC amendments: 0% (control), 10% and 20% (v/v). Seedlings were then subjected to controlled conditions under the same BC percentage. Biochar effects on seed germination were assessed measuring germination time and percentage, while effects on photosynthesis were assessed using leaf chlorophyll content (mg/m2) and photosynthetic efficiency (FV/FM). Plant growth was estimated by recording leaf number, longest leaf length and plant height. Biochar treatments had no negative effects on germination and early growth stage of the two species. Positive effects were found on the chlorophyll content of both species (ca. +8%) regardless of the treatment and on the leaf number (+30%), leaf length (+14%) and plant height (+48%) of Q. cerris (only with 10% BC). Biochar applications seem, therefore, a suitable method for increasing broad-leaved forest C stock in Italy.

Decreased in vitro bioaccessibility of Cd and Pb in an acidic Ultisol through incorporation of crop straw-derived biochar

Studies analyzing the in vitro bioaccessibility (BAc) of heavy metals in biochar-amended soils are currently lacking. The present study aimed to assess the metal BAc in Cd- and Pb-spiked acidic Ultisol samples treated individually with 2% (w/w) maize, rice, wheat, soybean, and pea straw-derived biochar. The results indicate that the Cd-BAc simulated in gastric phase (GP) decreased from 78.4% to 66.5–72.3% and the Pb-BAC decreased from 74.3% to 67.2–69.2%; however, the Cd-BAc in the intestinal phase (IP) decreased from 35.6% to 27.9–33.5% and the Pb-BAc decreased from 34.7% to 29.7–32.9% after 120 d of incubation with biochar application compared to the un-amended Ultisol. The Cd- and Pb-BAc in both GP and IP were significantly negatively correlated with soil pH, CEC, and organic carbon (P < 0.05), which increased after biochar application. The soybean straw-derived biochar amendment has the greatest potential to decrease the BAc of Cd and Pb in the GP and IP, owing to the highest level of CEC, SOC, TC and TN among all soil samples. Moreover, the BAc was positively correlated with the exchangeable, and exchangeable + carbonate-bound Cd and Pb fractions (P < 0.05), indicating these fractions had a dominant influence on the BAc of cationic heavy metals. Therefore, crop straw-derived biochar amendment can decrease the BAc of Cd and Pb in acidic Ultisol, and thus mitigate the health risks posed by these metals from incidental ingestion.

Life cycle assessment of novel biogeochemical cover versus conventional soil cover

The aim of this study is to evaluate the functional performance and environmental impacts of recently proposed biogeochemical cover (BGCC) system at a municipal solid waste landfill and compare with the conventional soil cover (SC) system. The functional performance of the cover systems was assessed through infiltration, methane emissions and slope stability analyses. In addition, life cycle assessment (LCA) was performed to evaluate the environmental impacts of the cover systems. The study also assessed the effect of various factors such as biochar manufacturing process, mode of transportation (fossil fuel powered vehicles versus electric powered vehicles), and transportation distance for raw materials supply on the environmental impacts. The results showed that the BGCC can significantly reduce the greenhouse gas emissions and global warming in comparison to the SC due to the use of biochar amended soil and basic oxygen furnace (BOF) slag. BGCC had 69 times more reduction in global warming impacts than SC which was attributed to the high methane oxidation potential of the biochar amended soil and carbon dioxide sequestration capacity of BOF slag. Moreover, BGCC had lesser environmental impacts than SC, mainly in the categories of eutrophication, carcinogens, non-carcinogens, respiratory effects, and ecotoxicity. Reducing transportation distance for biochar supply led to further reduction of the environmental impacts associated with the BGCC. For example, reducing the biochar procurement distance from 300 km to 100 km reduced the impacts from smog, acidification, eutrophication, and fossil fuel depletion by 14%, 13%, 5% and 14%, respectively. In addition, switching the vehicle from diesel powered to electric powered for transportation of raw materials led to significant reduction in fossil fuel depletion, smog, acidification and ecotoxicity in both BGCC and SC. For example, the fossil fuel depletion reduced by 97% and 39% in BGCC and SC, respectively by switching the fuel source. In addition, BGCC had overall positive impact on the human health and ecosystem whereas SC showed potential damage to human health. Overall, BGCC system proves to be an environmentally sustainable alternative to landfill cover system with significant potential for mitigation of greenhouse gases and odor from MSW landfills.

Effects of Biochar on the C Use Efficiency of Soil Microbial Communities: Components and Mechanisms

Biochar production and incorporation into soil is gaining momentum as a sustainable strategy for climate change mitigation, supported by ever increasing reports of significant carbon (C) sequestration in soil and reduction in greenhouse gas (GHG) emissions from the amended soils. With the progression in biochar testing and use, there is also emerging evidence that biochar induces C sequestration in soil, and that it may not be solely caused by its inherent chemical stability, but also by the complex microbially driven processes and an increase in C use efficiency (CUE) through soil microbial metabolism. This evidence contradicts the current paradigm that sees the microbial CUE decrease during the degradation of recalcitrant material due to thermodynamic constraints, as observed only in several short-term and pilot-scale trials. As the CUE in soil results from interactions between several abiotic and biotic factors, in this paper we examine the link between the biochar properties, soil physico-chemical properties and microbial physiology to explain the CUE increase reported for biochar-amended soils. Based on the large body of physico-chemical literature, and on the high functional diversity and metabolic flexibility of soil microbial communities, we hypothesize that the long-term stabilization of biochar-borne C in the soil systems is not only controlled by its inherent recalcitrance, but also by the cooperative actions of improved soil status and increased microbial CUE. Given that the current knowledge on this specific aspect is still poor, in this feature paper we summarize the state of knowledge and examine the potential impact of biochar on some factors contributing to the whole-soil CUE. We conclude that, beside its inherent recalcitrance, biochar weathering and oxidation in soil create physical and chemical conditions that can potentially increase the microbial CUE. While these processes stabilize the microbial processed C in soil and increase soil fertility, more data from long-term field trials are needed to model the relationship between the CUE and the MRT of biochar-borne C. Based on our hypotheses and relying upon analysis of the available literature, we also suggest possible research approaches that may contribute to filling the gaps in the current knowledge on the topic.

Biochar benefits carbon off-setting in blue-green infrastructure soils - A lysimeter study

Carbon sequestration with amendments in blue-green infrastructure soils could off-set anthropogenic greenhouse gas emissions to alleviate climate change. In this 3-year study, the effects of wheat straw and its biochar on carbon sequestration in an urban landscaping soil were investigated under realistic outdoor conditions using two large-scale lysimeters. Both amendments were carried out by incorporating pellets at 0–15 cm soil depth with an equivalent initial total carbon input of 2% of the dry soil weight. Soil carbon, carbon isotope ratios, dissolved carbon in leachates, CO2–C emissions, carbon fixed in above ground vegetation, soil water content, soil bulk electrical conductivity, and water infiltration rates, were then compared between the 2 lysimeters. After 3 years, we observed that, despite having a 17.2% lower vegetation growth, soil organic and inorganic carbon content was higher by 28.8% and 41.5%, respectively, in biochar as compared to wheat straw amended soil. Carbon isotope analysis confirmed the greater stability of the added carbon in the biochar amended soil. Water content was on average 23.2% and 13.0% in the straw pellet and biochar amended soil, respectively, whereas water infiltration rates were not significantly different between the two lysimeters. Overall, the incorporation of wheat straw biochar into soil could store an estimated 30 tonnes of carbon per hectare in city blue-green infrastructure spaces. Interviews involving institution stakeholders examined the feasibility of this biochar application. Stakeholders recognized the potential of biochar as an environment-friendly means for carbon offsetting, but were concerned about the practicality of biochar production and application into soil and increased maintenance work. Consequently, additional potential benefits of biochar for environmental management such as improving the quality of polluted run-off in stormwater treatment systems should be emphasized to make biochar an attractive proposition in sustainable urban development.

Effect of carrier gas change during sewage sludge or sewage sludge and willow pyrolysis on ecotoxicity of biochar-amended soil

Different pyrolysis conditions determine the properties of the biochar. The properties of biochar may affect directly or indirectly their influence on living organisms. The aim of this study was to determine the toxicity of biochar obtained under different conditions (temperature: 500 or 700 °C, carrier gas: N2 or CO2, feedstock: sewage sludge or sewage sludge/biomass mixture) after adding to the soil in long-term pot experiment (180 days). Biochars were added to the podzolic loamy sand at a 2% (w/w) dose. Samples were collected at the beginning of the experiment and after 30, 90 and 180 days. The bacteria Aliivibrio fischeri (luminescence inhibition – Microtox), the plant Lepidium sativum (root growth and germination inhibition test – Phytotoxkit F), and the invertebrate Folsomia candida (mortality and reproduction inhibition test – Collembolan test) were used as the test organisms. In the long-term perspective for most tests, changing the carrier gas from N2 to CO2 resulted in reduced toxicity of the biochar. A particularly beneficial effect of changing the gas to CO2 was observed for the solid-phase test with L. sativum. The CO2 during pyrolysis had the least beneficial effect on toxicity towards A. fischeri.

Acid-modified biochar increases grain yield and reduces reactive gaseous N losses and N-related global warming potential in alternate wetting and drying paddy production system

Biochar amended soils reduce fertilizer N losses and suppress greenhouse gas emissions. However, biochar can increase NH3 volatilization. H2SO4- modified biochar has been studied as a means to achieve the advantages of biochar while reducing volatilization, especially under alternate wetting and drying irrigation (IAWD). In contrast to continuously flooded irrigation (ICF), IAWD is a water-saving technology that repeatedly dries and re-floods fields. A 3-year field experiment was conducted with two irrigation regimes (ICF and IAWD) as main plots and 0 (control), 20 t ha−1 biochar, and 20 t ha−1 H2SO4-modified biochar as subplots. IAWD produced 7.6–14.8% more reactive gaseous N losses (NH3 and N2O) and emitted 2.02 times N-related global warming potential (GWPN) of ICF. Biochar increased NH3 volatilization by 35.6% in the first year and decreased it by 22.4% and 24.8% in the second and third years, respectively, while H2SO4-modified biochar decreased NH3 volatilization each year. The increased NH3 volatilization was caused by the higher NH4+ concentration and pH in the floodwater and surface soil due to increasing N inputs and alkalinity from biochar. The decrease in the following two years was attributed to pH returning to the pre-treatment level and continued biochar absorption of NH4+ from the floodwater. Both biochar and H2SO4-modified biochar significantly reduced seasonal N2O emissions. H2SO4-modified biochar coupled with IAWD mitigated the initial increases in NH3 volatilization and reactive gaseous N losses in the first year, and increased grain yield, decreased reactive gaseous N losses, and GWPN compared with the IAWD without biochar throughout the three years. The use of acid-modified biochar could produce higher grain yield with lower reactive gaseous N losses and GWPN for application in the IAWD paddy systems, which benefits sustainable agricultural production.

Contrasting effects of maize litter and litter-derived biochar on the temperature sensitivity of paddy soil organic matter decomposition.

Organic matter input regulates the rate and temperature sensitivity (expressed as Q10) of soil organic matter (SOM) decomposition by changing microbial composition and activities. It remains unclear how the incorporation of litter-made biochar instead of litter affects the Q10 of SOM decomposition. Using a unique combination of two-and three-source partitioning methods (isotopic discrimination between C3/C4 pathways and 14C labeling), we investigated: (1) how maize litter versus litter-made biochar (of C4 origin) addition influenced the Q10 of SOM (C3 origin) under 10°C warming, and (2) how the litter or biochar amendments affected the Q10 of 14C-labeled fresh organic matter (FOM) after long-term incubation. Compared with biochar addition, litter increased the rates and Q10 of mass-specific respiration, SOM and FOM decomposition, as well as the contents of SOM-derived dissolved organic C (DOC) and total phospholipid fatty acids (PLFA). Litter-amended soils have much higher activities (Vmax) of β-glucosidase, N-acetyl-β-glucosaminidase, and leucine aminopeptidase, suggesting larger enzyme pools than in soils with biochar. The Q10 of enzyme Vmax (1.6–2.0) and Km (1.2–1.4) were similar between litter-and biochar-amended soils, and remained stable with warming. However, warming reduced microbial biomass (PLFA) and enzyme activity (Vmax), suggesting decreased enzyme production associated with smaller microbial biomass or faster enzyme turnover at higher temperatures. Reductions in PLFA content and enzyme Vmax due to warming were larger in litter-amended soils (by 31%) than in the control and biochar-amended soils (by 4–11%), implying the active litter-feeding microorganisms have a smaller degree of heat tolerance than the inactive microorganisms under biochar amendments. The reduction in enzyme activity (Vmax) by warming was lower in soils with biochar than in the control soil. Our modeling suggested that the higher Q10 in litter-amended soils was mainly caused by faster C loss under warming, linked to reductions in microbial biomass and growth efficiency, rather than the slightly increased SOM-originated substrate availability (DOC). Overall, using straw-made biochar instead of straw per se as a soil amendment lowers the Q10 of SOM and FOM by making microbial communities and enzyme pools more temperature-tolerant, and consequently reduces SOM losses under warming.

Laboratory study of water infiltration and evaporation in biochar-amended landfill covers under extreme climate

Biochar has been used as an environment-friendly enhancer to improve the soil hydraulic properties. Previous studies focused on the effect of biochar addition for irrigation in agricultural soils. However, the understanding of the influence of biochar addition on water infiltration in compacted soils as used in landfill covers is limited. This study investigated the effects of peanut shell biochar addition on soil water infiltration with consideration of soil microstructure variations. The performance of biochar-amended soil was also explored under extreme rainfall and drought conditions. In this experiment, peanut shell biochar with particles finer than 0.25 mm was amended into compacted silty sand. Index soil properties and microstructure were observed. One-dimension (1-D) column tests and corresponding numerical modelling were carried out to investigate the performance of this cover material under different climate scenarios. The results suggested that the application of biochar can increase soil porosity, but a significant number of large pores (i.e., larger than 20 μm) was minimized. With the application of biochar, the soil covers thus become more efficient in preventing infiltration and percolation. This is also crucial to minimize the need for a relatively large thickness of soil cover. With an increase in porosity, the biochar can improve the soil water retention. Under extreme drought, the application of biochar can reduce the very low pore-water pressure (PWP) in soils by more than 50%. From all of these, peanut shell biochar can potentially be an eco-friendly and more sustainable solution for soil covers, even under extreme climate conditions.

Evaluating the Influence of Nitrogen Fertilizers and Biochar on Brassica oleracea L. var. botrytis by the Use of Fourier Transform Infrared (FTIR) Spectroscopy

The exponential growth of the human population requires an increasing application of nitrogen (N) fertilizers, causing environmental pollution. Biochar (B) amended soil has been suggested as a sustainable agricultural practice to improve crop yield and mitigate agricultural pollutants’ contamination. Evaluating the effect of fertilization on Brassica crops, in combination with spectral analysis, may specify changes in the chemical composition of the vegetable as a result of N fertilization. This study characterized cauliflower tissues treated with N fertilizer and biochar, employing Fourier Transform Infrared spectroscopy. The experiment was conducted in cauliflower mesocosms treated with two doses of N fertilizer (130 and 260 kg N ha−1) with or without B. Attenuated total reflectance fractions were used to characterize fractions of curds, leaves, stems, and roots in the infrared using a Fourier transform. Principal component analysis was performed to classify the main differences among cauliflower tissues concerning treatments. FTIR spectra of Brassica oleracea L. var. botrytis tissues were related to nitrogen-based agricultural practices. The specific molecules associated with functional groups in cauliflower tissues were phenols, amides, proteins, amines, and glucosinolates. Biochar amended soil resulted in higher peaks that correspond to the stretching of phenols and proteins. The application of sustainable nitrogen fertilizers might influence the absorption bands characteristic of cauliflower’s typical metabolites. The research allows the identification of Brassicaceae’s functional molecules with a potential agronomic application.

Effect of carrier gas during pyrolysis on the persistence and bioavailability of polycyclic aromatic hydrocarbons in biochar-amended soil

AbstractIn this study the persistence (based on extractable, Ctot) and bioavailability (based on freely dissolved content, Cfree) of polycyclic aromatic hydrocarbons (PAHs) in biochar-amended soil was investigated. Biochar produced at 500 or 700 °C from sewage sludge (BC) or sewage sludge and willow (W) mixture (BCW) in an atmosphere of nitrogen (N2) or carbon dioxide (CO2) was evaluated. The biochars were applied to the real soil (podzolic loamy sand) at a dose of 2% (w/w). The content of Ctot and Cfree PAHs was monitored for 180 days. The biochar production conditions determined the Ctot and Cfree PAHs in the soil. A change of carrier gas from N2 to CO2 caused an increase in Ctot PAH losses in the soil from 19 to 75% for the biochar produced from SL and from 49 to 206% for the co-pyrolyzed biochar. As regards Cfree PAHs, the change from N2 to CO2 increased the losses of Cfree PAHs only for the biochar derived from SL at a temperature of 500 °C (by 21%). In the soil with the other biochars (produced at 700 °C from SL as well as at 500 and 700 °C from SL/W), the Cfree increased from 17 to 26% compared to the same biochars produced in an atmosphere of N2.