Soil-biochar Mixtures Research Articles

Conazole fungicides epoxiconazole and tebuconazole in biochar amended soils: Degradation and bioaccumulation in earthworms

Biochar usage in agriculture becomes increasingly important for the improvement of soil properties. However, from the perspective of pesticides, biochar can influence exposure to pesticides of both target and non-target organisms and also pesticides’ fate in soil. Our study investigated degradation and bioaccumulation (in the Eisenia andrei earthworm) of two conazole fungicides, epoxiconazole and tebuconazole, added to high- and low-sorbing soils (by means of fungicides’ sorption measured beforehand) amended with low-, moderate- and high-sorbing biochars at 0.2% and 2% doses. We aimed to investigate the effects of contrasting soil and biochar properties, different doses of biochar in soil-biochar mixtures, and different compounds on the degradation and bioaccumulation. We also wanted to explore if the beforehand determined sorption of fungicides on individual soils and biochars is manifested somehow in their degradation and/or bioaccumulation in soil-biochar mixtures. The biochars’ presence in the soils promoted the degradation of fungicides with a clear effect of dose and soil, but less clear effect of biochar or compound. The bioaccumulation factors were higher in low-sorbing soil variants and also decreased with increasing biochar dose. For low-sorbing soil variants, the bioaccumulation was also influenced by the type of biochar corresponding to its sorbing potential and the possible effect on the bioavailability of the fungicides. Our results show that mixing of biochars with soils changes the fate and bioaccumulation of the conazole fungicides. However, the sorption results from original materials are not straightforwardly manifested in the more complex soil-biota system.

Interaction of biochar stability and abiotic aging: Influences of pyrolysis reaction medium and temperature

To improve soil quality, contaminated-soil can be amended with biochar, but the stability of biochar due to the exposure to the environment is not well elucidated. Furthermore, with the emerging introduction of CO2 as a reaction medium to increase the stability of biochar, a strategic study of reactive media for pyrolysis on biochar stability is required. To investigate the effect of aging and reaction medium on biochar stability, sawdust (SB), rice straw (RB), and spent coffee grounds (CB) were pyrolyzed using two distinct reaction media, N2 and CO2, at 300 °C and 700 °C for 4 h. Biochar alone was subjected to three artificial aging processes: wet-dry, freeze–thaw, and light exposure for 25 cycles, based on these results, soil-biochar mixtures were aged artificially using wet-dry and freeze–thaw. Then, the leaching potential of dissolved organic matter (DOM) and As mobility were compared. This study showed that the aging processes increased levels of DOM leaching and wet-dry aging accelerated DOM leaching and As mobility most significantly. Weathered biochars released 3.7 (SB), 8.9 (RB), and 5.2 (CB) times more DOM than fresh biochar, and As mobility increased by factors of 5.4 (SB), 16.3 (RB), and 13.7 (CB) compared to soil-only aging systems without biochar. Moreover, the CO2 reaction medium produced more stable biochar and lowered slightly DOM leaching and As mobility versus using N2. This study suggests that it is important to consider not only the immediate effect of applying biochar to soil but also the effects of various aging of biochar over time.

Effects of Biochar, Plant Density and Spacing on Growth and Yield of Rice in a Tropical Inland Valley Swamp

Biochar has been confirmed to boost soil fertility and crop efficiency. The study aimed to examine the impacts of different combinations of biochar, plant hill and spacing on the growth and yield parameters of rice (<i>Oryza sativa</i> L.) var NERICA L 19 in an inland valley swamp in Sierra Leone. The experiment was performed in a Randomized Complete Block Design using eight treatment combinations including: two levels of Biochar-soil mixtures (10 t ha^-1 and 0 t ha^-1), two levels of plant density per hill (1 seedling per hill and 2 seedlings per hill), and two levels of plant spacing (25 cm and 20 cm). Growth parameters were conducted at 4, 6, 8, and 10 weeks after transplanting (WAT), while yield parameters were measured at harvest. Biochar hill and spacing had no significant effect on plant height, leaf area, grain yield, straw yield, and harvest index, but biochar plant spacing had a significant effect on tiller number. Biochar significantly enhanced plant growth (tiller number) and yield attribute traits such as panicle number and straw yield. The potential of gliricidia biochar in supporting increased growth and yield suggest its exploitation for both straw and grain yield productivity of rice in the IVS. Residual gliricidia biochar could be also exploited in future studies to determine their benefit in enhancing grain yield in IVS rice.

Mechanical behavior, under four-point bending test, of compositions with soil, bio-char and charcoal

Soil stabilization for use in pavement sublayers has been established in Geotechnical En-gineering as an option for pavement construction. In this context, certain alternative materials stand out, such as coal and biochar, which are able to fulfill this function when added to the soil, being the object of study in the present research. These products originated from char-coal furnaces and biomass carbonization under low oxygen atmosphere. In the present study we evaluated the natural soil and compositions according to the four-point bending test, for simulating vehicle tire-loads on the pavement. For this purpose, we molded prismatic speci-mens with natural soil (NS) typical of the Amazon region, with natural soil-10% charcoal (SCH) and soil-10% biochar (SBC). It was verified that the soil-biochar mixture (SBC) pre-sented better results, culminating in higher values of complex modulus when compared to the natural soil (NS) and soil-charcoal mixtures (SCH). Regarding the phase angle parameter and the analyzed set (NS, SCH e SBC), values close to zero were observed. Therefore, this article presents the possibility of using alternative materials for executing road systems with better performance.

Fresh biochar application provokes a reduction of nitrate which is unexplained by conventional mechanisms

Soil-applied biochar has been reported to possess the potential to mitigate nitrate leaching and thus, exert beneficial effects beyond carbon sequestration. The main objective of the present study is to confirm if a pine gasification biochar that has proven able to decrease soil-soluble nitrate in previous research can indeed exert such an effect and to determine by which mechanism. For this purpose, lysimeters containing soil-biochar mixtures at 0, 12 and 50 t biochar ha−1 were investigated in two different scenarios: a fresh biochar scenario consisting of fresh biochar and a fallow-managed soil, and an aged biochar scenario with a 6-yr naturally aged biochar in a crop-managed soil. Soil columns were assessed under a mimicked Mediterranean ambient within a greenhouse setting during an 8-mo period which included a barley crop cycle. A set of parameters related to nitrogen cycling, and particularly to mechanisms that could directly or indirectly explain nitrate content reduction (i.e., sorption, leaching, microbially-mediated processes, volatilisation, plant uptake, and ecotoxicological effects), were assessed. Specific measurements included soil solution and leachate ionic composition, microbial biomass and activity, greenhouse gas (GHG) emissions, N and O isotopic composition of nitrate, crop yield and quality, and ecotoxicological endpoints, among others. Nitrate content reduction in soil solution was verified for the fresh biochar scenario in both 12 and 50 t ha−1 treatments and was coupled to a significant reduction of chloride, sodium, calcium and magnesium. This effect was noticed only after eight months of biochar application thus suggesting a time-dependent process. All other mechanisms tested being discarded, the formation of an organo-mineral coating emerges as a plausible explanation for the ionic content decrease.

Sorption and degradation of imidacloprid and clothianidin in Chinese paddy soil and red soil amended with biochars

Application of biochar technology in the remediation of organic contaminated soils has drawn growing interest in recent years. In this study, sorption and degradation of two typical neonicotinoid insecticides, imidacloprid (IMI) and clothianidin (CLO) in Chinese typical paddy soil and red soil amended with six kinds of biochars were investigated. The results showed that surface area (SA), pH, total organic carbon and dissolved organic carbon (DOC) of the two soils all increased after biochar amendment, while H/C decreased. With biochar pyrolyzing temperature (PT) increasing from 300 °C to 700 °C, the sorption of the two insecticides on biochar–soil mixtures increased by more than 4.3-fold, due to the increasing SA and decreasing H/C. The acidic pH of the two tested soils also favored the enhanced sorption of the insecticides by removing the ash on biochar. The amendment of low-PT (300 °C) biochar promoted the biodegradation of IMI and CLO by 11.3–41.9% via providing more DOC and available N for microorganisms, while inhibiting the chemical degradation. Oppositely, the high-PT (500–700 °C) biochars inhibited the biodegradation of the insecticides by decreasing their bioavailability and promoted the chemical degradation by providing mineral active groups, and generating ·OH and other free radicals. In addition, soil type also affected the effects of biochar remediation. The highest 60-day degradation extent was achieved for CLO (90.5%) and IMI (81.4%) in paddy soil by adding biochar derived from pig manure at 700 °C PT. In summary, the effect of biochar on the fate of organic contaminants in soil is a comprehensive result involving several processes and a systematic study considering the type and property of biochar and soil is needed to optimize biochar technology.

Changes in phosphorus fractions in three tropical soils amended with corn cob and rice husk biochars

ABSTRACT The formation of phosphorus (P) compounds including iron-P, aluminum-P and calcium-P in highly weathered tropical soils can be altered upon biochar addition. We investigated the effect of corn cob biochar (CC) and rice husk biochar (RH) pyrolyzed at three temperatures (300°C, 450°C and 650°C) on phosphorus (P) fractions of three contrasting soils. A 90d incubation study was conducted by mixing biochar with soil at a rate of 1% w/w and at 70% field capacity. Sequential P fraction was performed on biochar, soil and soil-biochar mixtures. Increase in most labile P (resin-Pi, NaHCO3-Pi) and organic P fraction (NaHCO3-Po + NaOH-Po) in CC and RH biochars were inversely related to increasing temperature. HCl-Pi and residual P increased with increasing temperature. Interaction of CC and RH with soils resulted in an increase in most labile P as well as moderately labile P (NaOH-Pi) fractions in the soils. CC increased most labile P in the soils more than RH. The increase in most labile P fraction in soils was more significant at relatively lower temperatures (300°C and 450°C) than 650°C. However, the increase in HCl-Pi and residual P of the soils was more predominant at high temperature (650°C). The study suggested that biochar pyrolyzed at 300–450°C could be used to increase P bioavailability in tropical soils.

Nutrient uptake and growth of potato: Arbuscular mycorrhiza symbiosis interacts with quality and quantity of amended biochars

AbstractAims: The aim of this study was to explore interactive effects between quality (types) and quantity (application rates) of biochar as well as of arbuscular mycorrhiza (AM) symbiosis on the growth of potato plants.Methods: A low P sandy loam soil was amended with 0%, 1.5%, or 2.5% (w/w) of either of 4 types of biochar, which were produced from wheat straw pellets (WSP) or miscanthus straw pellets (MSP) pyrolyzed at temperatures of either 550°C or 700°C. Potato plants grown in pots containing the soils or soil biochar mixture were inoculated with or without AM fungus (AMF), Rhizophagus irregularis. The experiment was carried out under fully irrigated semi‐field conditions and plants were harvested 101 days after planting.Results: Application of high temperature biochar decreased growth, biomass and tuber yield of potato plants, while the low temperature biochar had a similar effect on yield as plants grown without biochar amendment. Total biomass of potato plants were decreased with the increasing rate of biochar. Arbuscular mycorrhizal fungus inoculation stimulated the growth of potato plants in all organs, increased tuber biomass significantly in 1.5% MSP700 amended plants, and to a lesser degree for WSP700, MSP550, and WSP550. In addition, plant biomass gain was linearly related to N, P, and K uptake, the ratio of P to N in the leaf of plants indicated that all treatments were mainly P‐limited. A multiple linear regression using P uptake and biochar rate as independent variables explained 91% of the variation in total biomass. The single effect of AMF inoculation, type and rate of biochar affected plant N, P and K uptake similarly. While AMF inoculation significantly increased P uptake in potato plants grown in soil with WSP700 or MSP700 despite of the rate of biochar. In general, application of biochar significantly increased AMF root colonization of potato plants.Conclusions: The application of MSP550 at 1.5% combined with AMF stimulated growth of potato the most.Furthermore, the results indicated that the interactive effect of AMF inoculation, biochar type and application rate on potato growth to a large extent could be explained by effects on plant nutrient uptake.

Characterization and carbon mineralization of biochars produced from different animal manures and plant residues

Renewing carbon and re-establishing it again in the soil is one of the valuable means to cope with climate change. There are many technologies for carbon apprehension and storage, but the most important one gaining attention is biochar technology. So, to carbonize and return different biological materials back to the farmland, a comprehensive study was proposed to characterize and evaluate the carbon (C) mineralization of biochars produced from different animal manures and crop straws. Six types of biochars were prepared from animal manures (poultry litter, swine and cattle manures) and crop straws (rice, soybean, and corn straws). The biochars were analyzed for chemical characteristics (elemental variables, thermal decomposition, cation exchange capacity, pH, electrical conductivity, specific surface area, and surface functional groups) and an incubation experiment was conducted to evaluate C mineralization from soil biochar mixture. Biochars produced from crop straws resulted to have more C as compared to the biochars produced from animal manures. Concentration of nitrogen was low, while P, K, Ca, and Mg were found reasonably higher in all biochars except swine manure biochar. The plant-derived biochars presented lower CO2 emissions when incorporated to soil at 1 and 2% of C. Varying but all the biochars prepared represented an alkaline pH. Biochars prepared from the crop straws resulted to have more C, alkaline in nature, high CEC, low CO2 emissions, can sequester C and more suitable to enhance the soil fertility in comparison to biochars produced from other sources.

Biochar impacts on sorption-desorption of oxytetracycline and florfenicol in an alkaline farmland soil as affected by field ageing

Few studies have been conducted to examine the effects of biochar amendment on sorption and desorption of antibiotics in alkaline soils under field ageing conditions. In this study, sorption and desorption of two antibiotics (oxytetracycline (OTC) and florfenicol (FFC)) were investigated for a calcareous farmland soil with different biochar treatments (1 and 5 wt%, including fresh and aged soil-biochar mixtures). The fresh and recovered field-aged biochar particles were characterized by various methods. The results indicated that, after one-year-field-ageing, the abundance of amorphous carbon on biochar surface and the carbon content of biochar particles decreased markedly whereas the surface area and the oxygen-containing functional groups increased. It was found in batch experiments that the effects of biochar application and ageing on sorption and desorption characteristics were apparently different between the two antibiotics. OTC (a more hydrophobic and less polar antibiotic) showed much higher sorption capacity than FFC. Biochar-derived dissolved organic matter (DOM) was found to compete for sorption sites on soil surface, particularly for the 5 wt%-freshly-amended soil. The adherent excessive DOM had lowered OTC sorption and enhanced its partitioning to the solution phase. On the other hand, enhanced partitioning of FFC to the amorphous carbon of biochar accounted for the observed increase of its sorption to the soils with fresh biochar amendment. However, the above effects on sorption affinity for both antibiotics weakened after ageing in the studied calcareous purple soil. Thus, due attention should be paid to the potential risk of leaching increase of OTC in alkaline soils upon biochar amendment, particularly within the very beginning period after application.

Effect of biochar on the mobility and photodegradation of metribuzin and metabolites in soil‒biochar thin-layer chromatography plates

ABSTRACTBiochars obtained by biomass pyrolysis have been proposed as a soil amendment to improve soil properties and fertility as well as to retain pesticides and other environmental contaminants. The present study investigates the degradation of metribuzin herbicide and its metabolites deamino- (DA), deaminodiketo- (DADK) and diketo- (DK) metribuzin under simulated solar light and dark conditions as well as their mobility using TLC plates coated with soil and soil‒biochar mixtures at 1% and 5% w/w ratio. Biochar was characterised by X-Ray diffraction, porosimetry, scanning electron microscopy and Fourier transform infrared spectroscopy. Degradation under light conditions followed biphasic kinetics, with bi-exponential model fitted better for the soil substrate, while the Gustafson–Holden model was found more appropriate to describe degradation kinetics in 1% soil/biochar mixture. In soil, DA presented the lowest degradation rate (DT50:440.9 h), followed by metribuzin (DT50:208.0 h), DADK (DT50:110.8 h) and DK (DT50:106.5 h). The addition of biochar reduced drastically the degradation or even inhibited the photolytic process for the studied reaction period. The mobility retention factor (Rf) in soil ranged from 0.49 for metribuzin to 0.63 for DADK. The addition of biochar practically immobilises the compounds in the surface layer as Rf ranged from 0.14 to 0.10 for metribuzin and from 0.23 to 0.16 for DADK in soil/biochar mixtures 1% and 5%, respectively. In conclusion, the addition of biochar reduced dramatically the photodegradation rates as well as the mobility of metribuzin and its metabolites due to increased adsorption.

Amelioration in nutrient mineralization and microbial activities of sandy loam soil by short term field aged biochar

The aging of biochar is an important parameter for its sustainable application. However, data on the impact of field-aging biochar on soil biological properties is limited. In this study, the impact of three months aged biochar soil mixture and fresh biochar soil mixture on the physico-chemical characteristics (morphology, functional groups, cation exchange and water holding capacities) and biological activity (microbial and soil enzymes) was compared. Cymbopogon winterianus-derived biochar was used for the experiment at three different application rates. The physico-chemical properties of soil collected at different time points suggested that weathering of biochar soil mixture significantly increases the labile organic carbon and cation exchange capacity. However, a decrease in pH and water holding capacity was also observed. In the aged biochar-soil mixture, the rate of mineralization was higher as compared to the fresh biochar-soil mixture. It provided better sites for adsorption of NH4-N and NO3-N. Aged soil biochar mixture had higher microbial and enzymatic activities (dehydrogenase, acidic and alkaline phosphatase and urease) as compared to fresh biochar soil mixture except for β-glucosidase. Our results suggest that short-term field weathering of biochar would be able to improve the soil biological properties significantly.

Pine sawdust biochar as a potential amendment for establishing trees in Appalachian mine spoils

Early growth and survival of tree seedlings is often poor on reclaimed coal surface mines in Appalachia. Biochar produced in bioenergy generation has potential for use as an amendment to improve seedling performance. Mine soil was collected from a recently reclaimed coal surface mine in Wise County, Virginia and mixed with loblolly pine (Pinus taeda L.) sawdust biochar, simulating application rates of 2.3, 11.2 and 22.5 Mg ha-1. Unplanted leaching columns and 4 L tree planting pots were filled with these biochar-soil mixtures, plus controls of pure mine soil and pure biochar. For the tree planting pots, additional pots were created where the biochar was applied as a topdressing at the same application rates as in the mixtures. One-year-old seedlings of both American sycamore (Platanus occidentalis L.) and black locust (Robinia pseudoacacia L.) were planted. Unplanted leaching columns were leached with collected rainwater for six months to simulate weathering. Trees were grown for one growing season. Black locust had higher average above-ground dry woody biomass (24.4 g) than American sycamore (17.0 g), and also higher below-ground biomass (61.0 g compared to 30.2 g). The pure biochar produced greater average below-ground biomass (99.9 g) than the pure mine soil (46.9 g). All of the biochar treatments produced greater average above-ground woody biomass (19.1 g – 33.4 g) than the pure mine soil (10.9 g). After weathering, biochar provided less available soil phosphorus, calcium and iron than the mine soil itself while increasing soil carbon and organic matter. High (22.5 Mg ha-1) biochar applications increased soil volumetric water holding capacity to 18.6% compared to 13.4% for pure mine soil. Naturally-occurring herbaceous biomass in the pots was negatively correlated with above-ground woody biomass at r = -0.483. Topdressing and full incorporation of biochar were not significantly different in their effects on biomass. Results suggest that pine biochar either broadcast at 2.3 - 22.5 Mg ha‑1, or mixed in planting holes with backfill soil, will promote faster above-ground growth and larger root systems in seedlings in mine soils. Further studies should test these methods in the field over multiple years and further refine recommendations of the rate of biochar to use and how best to apply it. New systems are being developed in Appalachia to produce biofuels and biochar from local biomass and to recycle biochar into the land base to enhance future biomass productivity. Applying 4 L of biochar mixed with the backfill of newly-planted trees is the top recommended practice for tree performance.

Interactions between aged biochar, fresh low molecular weight carbon and soil organic carbon after 3.5 years soil-biochar incubations

Biochar has been considered a stable additive for long-term soil carbon (C) storage and climate change mitigation. However, our understanding of the long-term interactions between aged biochar, soil organic C (SOC), and fresh low molecular weight C compounds (LMW-C) is still limited. In addition to the changes in the chemical properties of biochar and the SOC after aging, biochar stability and C sequestration potentials might be affected by the LMW-C availability. After 3.5 years of incubation, aged soils and aged soil-biochar mixtures (4 atom‰ 13C enriched grass-derived biochar, 10% addition rate) of two different soil types were used in this study, with or without the addition of LMW-C. The 13C natural abundance of the LMW-C was manipulated by mixing cane sucrose (C4) and beet sugar (C3) to make it different from or equal to the native SOC isotopic signature of the two soil types, which allowed the partitioning of the LMW-C and biochar C from the SOC in non-biochar and biochar addition treatments, respectively. We traced the 13C in the cumulative CO2, microbial biomass C (MBC), and dissolved organic C (DOC) at the beginning and the end of the 28 days of incubation. Results indicated that this aged biochar was not as effective for SOC protection as it was when fresh. Aged biochar caused significant increases in the native SOC-derived CO2 compared to non-biochar treatment during the 3.5 years of aging. Within the 28 days of incubation, aged biochar not only promoted the total CO2 emission but also did not limit the priming effect of LMW-C on native SOC mineralization. SOC-derived DOC in the aged soil-biochar mixture was significantly higher than that in the aged soil, which further increased the SOC loss. A decline in the SOC stability with aged biochar might be associated with the attenuated sorption of SOC on aged biochar, the decline in bulk density with the high biochar addition rate, and a modified microbial community. The priming of aged SOC mineralization with the addition of LMW-C might be associated with the enhanced microbial N demand in aged soils and soil-biochar mixtures. The effect of aged biochar on the soil DOC and the effect of LMW-C on the aged biochar and SOC stabilities should be further investigated in field conditions, under continuous fresh C inputs, to better evaluate the effects of biochar on long-term SOC storage.

Quantity and quality changes of biochar aged for 5 years in soil under field conditions

To better use biochar as a sustainable soil management and carbon (C) sequestration technique, it is necessary to understand the biochar aging process in soil, as its quantity and quality likely vary over time. In this study, we quantified the biochar amount after five years of application in an arable field that applied fresh biochar at rates of 30, 60 and 90Mgha−1, and measured the physicochemical properties of biochar before and five years after amendment. The aged biochar in soil was quantified by the method of loss on ignition (LOI). After it was isolated from the soil-biochar mixture by hand, biochar structure was observed by scanning electron microscopy (SEM), and specific surface area and pore volume were measured by Brunauer, Emmett and Teller method (BET). Additionally, biochar chemical properties were measured by elemental analysis, solid-state 13C nuclear magnetic resonance (NMR), Fourier Transform Infrared spectra (FTIR) and analytical pyrolysis (Py–GC/MS).We observed that, after five years, nearly 40% biochar was diminished in the 0–20 cm soil layer for all treatments. The specific surface area (SSA) of aged biochar increased 98–114.3% relative to the fresh biochar. However, the average pore diameter decreased in the aged, relative to fresh biochar, which was proved from the SEM result, indicating new small pores were formed during aging process. Moreover, SEM also showed that aged biochar had a smoother surface than that of the fresh one, suggesting that either labile matter was leached or minerals was dissolved. Additionally, aged biochar C content increased by 2.44% and oxygen (O) content decreased by 2.81%. However, no chemical structural differences were found between the aged biochar and the fresh one, indicating that the biochar used in this study was relatively recalcitrant even in field conditions (wetting/drying, freezing/thawing cycling and tillage). These results improved our understanding of the processes behind carbon sequestration and the potential effects of biochar on soil properties.

DNA extraction efficiency from soil as affected by pyrolysis temperature and extractable organic carbon of high-ash biochar

Biochar additions to soil have, in some cases, been shown to reduce the DNA extraction efficiency, but the mechanisms remain unclear and commonly used high-ash biochars have not been investigated. We studied the effects of pyrolysis temperatures (300 or 700 °C), post-pyrolysis extractable organic carbon (separating acetone extractable C, AeC), and soil incubation on DNA extraction efficiency using high-ash swine manure biochar. We used quantitative PCR to measure the extraction efficiency of an internal DNA standard (Aliivibrio fischeri) added to samples before extraction. DNA extraction efficiency from biochars decreased by 39% as pyrolysis temperature increased from 300 to 700 °C (p < 0.05). AeC from biochar 300 °C increased DNA extraction efficiency for biochars made at both pyrolysis temperatures and when added to biochar 700 °C, the extraction efficiency increased by 52% (p < 0.05). Incubation in soil increased DNA extraction efficiency from isolated biochar particles by up to 28% (main effect p < 0.05). However, biochar-soil mixtures had up to 24% lower DNA extraction efficiency compared to what would be predicted based on a simple mixing model of incubated soil and separated biochars. Biochar pyrolysis temperature, extractable C, and incubation with soil were all associated with changes in DNA extraction efficiency. The differences in DNA extraction efficiency indicated that caution must be exercised when comparing microbial abundance and diversity with different biochar additions, even for high-ash biochars.

Short-term greenhouse emission lowering effect of biochars from solid organic municipal wastes

Qatar economy has been growing rapidly during the last two decades during which waste generation and greenhouse gas emissions increased exponentially making them among the main environmental challenges facing the country. Production of biochar from municipal solid organic wastes (SOWs) for soil application may offer a sustainable waste management strategy while improving crop productivity and sequestering carbon. This study was conducted to (1) investigate the physicochemical parameters of biochars for SOW, (2) select the best-performing biochars for soil fertility, and (3) evaluate the potential benefits of these biochars in lowering greenhouse gases (GHGs) during soil incubation. Biochars were produced from SOW at pyrolysis temperatures of 300–750 °C and residence times of 2–6 h. Biochars were characterized before use in soil incubation to select the best-performing treatment and evaluation of potential GHG-lowering effect using CO2 emission as proxy. Here, soil–biochar mixtures (0–2%w/w) were incubated in greenhouse settings for 120 days at 10% soil moisture. Soil properties, such as pH, EC, TC, and WHC, were significantly improved after soil amendment with biochar. Two biochars produced from mixed materials at 300–500 °C for 2 h and used at 0.5–1% application rate performed the best in enhancing soil fertility parameters. A significant decrease in CO2 emission was observed in vials with soil–biochar mixtures, especially for biochars produced at 500 °C compared the corresponding raw materials which exhibited an exponential increase in the CO2 emission. Hence, application of biochar to agricultural soils could be beneficial for simultaneously improving soil fertility/crop productivity while sequestering carbon, thereby reducing anthropogenic emissions of GHGs.

Impacts of Woody Biochar Particle Size on Porosity and Hydraulic Conductivity of Biochar-Soil Mixtures: An Incubation Study

ABSTRACTBiochar improves soil performance by altering soil physical characteristics. To understand the effect of biochar particle size on soil hydrology, we measured the hydraulic conductivity (Ks) of biochar-soil mixtures. To better understand how physical properties influenced Ks, skeletal and (bulk density (, the water saturation (S), and the porosity (Ф) of mixtures were measured. A sandy loam soil was mixed with two woody biochar particle sizes (1–2 and <1 mm). All used biochars significantly decreased Ks compared to soil but this reduction for finer biochars was more distinct. When finer particles of low and high-tempered biochars were applied Ks decreased 14.3% and 18.9% while coarser particles reduced Ks 13.9% and 17.5%, respectively. Also, all biochars increased total, effective, inter and intraporosity of mixtures compared to control after 180 days. Negative correlation between Ks and porosity demonstrates the increase of porosity isn’t necessarily providing flow paths and thus doesn’t have a positive influence on Ks. Decrease of Ks through the addition of fine biochars was because they filled spaces between soil particles, which increased tortuosity and reduced pore throat size. Also, the decrease of Ks associated with coarser biochars was caused by the bimodal particle size distribution, resulting in more compact packing and tortuosity.

Effect of Biochar Amendment and Ageing on Adsorption and Degradation of Two Herbicides

Biochar amendment can alter soil properties, for instance, the ability to adsorb and degrade different chemicals. However, ageing of the biochar, due to processes occurring in the soil over time, can influence such biochar-mediated effects. This study examined how biochar affected adsorption and degradation of two herbicides, glyphosate (N-(phosphonomethyl)-glycine) and diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) in soil and how these effects were modulated by ageing of the biochar. One sandy and one clayey soil that had been freshly amended with a wood-based biochar (0, 1, 10, 20 and 30% w/w) were studied. An ageing experiment, in which the soil-biochar mixtures were aged for 3.5 months in the laboratory, was also performed. Adsorption and degradation were studied in these soil and soil-biochar mixtures, and compared to results from a soil historically enriched with charcoal. Biochar amendment increased the pH in both soils and increased the water-holding capacity of the sandy soil. Adsorption of diuron was enhanced by biochar amendment in both soils, while glyphosate adsorption was decreased in the sandy soil. Ageing of soil-biochar mixtures decreased adsorption of both herbicides in comparison with freshly biochar-amended soil. Herbicide degradation rates were not consistently affected by biochar amendment or ageing in any of the soils. However, glyphosate half-lives correlated with the Freundlich Kf values in the clayey soil, indicating that degradation was limited by availability there.

Dynamic changes in atrazine and phenanthrene sorption behaviors during the aging of biochar in soils.

The objective of this study was to elucidate the dynamic changes in the properties of biochar-amended soil and their sorption capacity for typical organic contaminants with increasing contact time between biochar and soil. To do so, biochars that were produced from pig manure at two temperatures were added to two soils, and the sorption behaviors of atrazine and phenanthrene (Phen) on soil-biochar mixtures aged for different times were investigated. Soils freshly amended with biochars showed a dramatic increase in the sorption of atrazine (up to 23.4 times at C e=0.01 S w) and Phen (up to 3.12 times at C e=0.01 S w) compared to the bare soils without biochars. The physicochemical properties of soil-biochar mixtures changed with aging time, which in turn affected the sorption capacity. After the biochar produced at 300°C (BC300) was aged in soil, the sorption of atrazine and Phen by black soil (BS) and fluvo-aquic soil (FS) both increased by different extents, except the sorption of Phen on BS. However, after the biochar produced at 700°C (BC700) was aged in soil, the sorption of atrazine on the two soils decreased markedly, which was sill 56.3% higher than that on the original soil, while an opposite trend was observed for Phen on the two soils. The complex change patterns could be due to the different dominant sorption mechanisms for different biochars and chemicals.