Soil-biochar Mixtures Research Articles

Influence of biochar in the calcite precipitation of sandy soil using sporosarcina ureae

The microbially induced calcium carbonate precipitation (MICP) technology is an emerging novel and sustainable technique for soil stabilization and remediation. MICP, a microorganism-mediated biomineralization process, has attracted interest for its potential to enhance soil characteristics. The inclusion of biochar, a carbon-rich substance formed by biomass pyrolysis, adds another degree of intricacy to this process. The study highlights the impact of the combination of biochar and MICP together, using a bacterium, Sporosarcina ureae, on soil improvement. This blend of MICP and biochar improved the soil in terms of its geotechnical properties and also enabled the sequestering of carbon safely. It was observed that addition of 4% biochar significantly increased the soil's shear strength parameters (c and φ) as well as its stiffness after 21 treatment cycles. This improvement was because the calcium carbonate precipitate, which acts as a crucial binding agent, increased significantly due to microbial action in the soil-biochar mixture compared to the pure soil sample. The excess carbonate precipitation on account of biochar addition was verified through SEM-EDAX analysis where the images showed noteworthy carbonate precipitation on the surface of particles and increment in the calcium mass at the same treatment cycles when compared with untreated sand. The collaboration between MICP and biochar effectively increased the carbon sequestration within the sand sample. It was observed that at 21 cycles of treatment, the carbon storage within the sand sample increased by almost 3 times at 4% biochar compared to sand without any biochar. The statistical analysis further affirmed that strength depends on both biochar and the number of treatment cycles, whereas carbon sequestration potential is primarily influenced by the biochar content alone. This strategy, as a sustainable and environmentally friendly approach, has the potential to reform soil improvement practices and contribute to both soil strength enhancement and climate change mitigation, supporting the maintenance of ecological balance.

Utilization of cotton gin waste biochars for agronomic benefits in soils

AbstractCotton gin waste (CGW) is produced in large quantities (1–1.5 × 106 metric ton/year) in the Texas High Plains (THP), one of the largest cotton-producing regions in the USA. We examined locally supplied CGW for soil amendment as biochar (CGW-BC) with a view toward rainfed cropping systems, which will likely become increasingly necessary due to declines in groundwater availability for irrigation. Sixteen unique biochar samples were produced under varying conditions of time, temperature, and post-processing wash in a muffle furnace. We performed material characterization on the biochar. We then incubated CGW-BC samples that seemed favorable for increasing the water holding capacity increase for 10 days with local, rainfed, clay loam soil. We found that increasing the pyrolysis time and temperature decreased the biochar yield but only up to 40 min. Beyond 40 min, the yield did not decrease further. Additionally, the majority of mass loss occurred during pyrolysis and not during crush-sieving or postproduction washes. CGW-BC produced at higher temperatures and for longer times had greater thermal stability. This interesting aspect of thermal stability, which did not always follow strict time‒temperature trends, may be because cotton gin waste is a heterogeneous material. We found that the addition of acid decreases the mineral content while lowering the thermal stability of lower temperature (450 °C) biochars. Regarding the CGW-BC surface area, we found that higher temperatures generally increase the micropore surface area. Using a GAB isotherm, water vapor surface area did not correlate with the highest WHC when water was added to the soil. In fact, biochar, which was pyrolyzed in less time at a lower temperature and with the use of acid washing, better held the water in soil-biochar mixtures. The measurements suggested that CGW-BC could be a valuable soil amendment that could increase the WHC without adversely increasing the pH. Our initial investigation revealed how scaled-up production of CGW-BC for soils might be economically and sustainably pursued for use in rainfed cropping, deficit irrigation, or ranchlands.

Identifying biochar production variables to maximise exchangeable cations and increase nutrient availability in soils

Biochar is a product of the thermal treatment of sustainably sourced organics or waste biomass, which enhances nutrient availability and exchangeable cations after soil application. Biochar feedstock is one of the primary factors influencing the availability of exchangeable cations in biochar and soil-biochar mix. However, this influence is not satisfactorily understood due to contrasting data among literature for the cation exchange capacity (CEC) and the lack of standard analysis methods for CEC of biochar and soil-biochar mixtures. Therefore, this research was conducted to assess cation exchange in contrasting soil-biochar mixes, where CEC is measured as (1) the sum of base cations (Na+, K+, Mg 2+, and Ca2+) displaced by ammonium acetate (CEC-BC) and (2) NH4+ displaced by potassium chloride (CEC-NH4+). For the first time, we have evaluated CEC-BC and CEC-NH4+ in 21 different biochar samples using a modified method. We then used 12 representative biochars with 3 soil types (2% w/w biochar) and provided insights on relative changes in CEC-BC and individual base cations. Some previous studies have indicated a relationship between CEC and surface area and a degree of additivity in the resulting CEC of soil-biochar mixes. However, our study demonstrates an absence of these correlations and a lack of additivity in the representative biochar products. We found that biochar prepared from mixed garden wastes can increase K+ or Ca2+ in loamy or sandy soils and mitigate potential soil sodicity problems in loamy soils. However, a clayey soil may or may not need biochar for the specific purpose of increasing exchangeable cations. Our results revealed that biochar prepared from hardwood or mixed garden waste can retain NH4+ and deliver it to soil acting as a sink and source for soil nutrients.

Enhancing herbicides sorption in sodic soils through biochar amendment : A promising approach for sustainable agriculture

This study is essential for assessing the binding capacity of Prosopis wood biochar to commonly used herbicides, Pretilachlor and Pendimethalin. Understanding their sorption dynamics at varying biochar application rates and exposure times is crucial for sustainable and effective herbicide management in intensively farming agricultural fields and for reducing environmental contamination. The Prosopis wood biochar was produced in an earthen kiln at 300-350°C. The batch experiment was conducted to study the sorption potential of biochar additions at rates of 0, 5, and 10 t ha-1. The herbicides were added to the homogenized soil-biochar mixes at zero, whole, twice, and four times the recommended dose. The sorption of the herbicides by soil biochar mixture was studied for 12 and 24 hours. The result showed that Pendimethalin sorption increased with biochar application rate, requiring 24 hours for 95% sorption at 4X dose without biochar (77.95 mg/kg soil) and 12 hours with 10 t/ha biochar (75.82 mg/kg soil). The Kd value increased with biochar application (0.57-77.95 mg/kg soil) and decreased with pendimethalin application (77.95-3.04 mg/kg soil). Maximum sorption (95%) was attained within 12 hours for 1X and 2X rates and 24 hours for 4X rates when biochar was added. This demonstrated that although pendimethalin residue in the soil can be immobilized by adding biochar within 8 hours at lower rates, more than 24 hours were required when pendimethalin was applied at higher rates or repeatedly. Biochar can be used to reduce pendimethalin leaching in agricultural fields, especially sodic soils, at higher application rates.

Persistent free radicals generated from a range of biochars and their physiological effects on wheat seedlings

Biochar is a promising soil conditioner and environmental remediation material. However, the amount, type, and environmental effect and risk of persistent free radicals (PFRs) associated with biochar need to be better understood. Thus, this study characterized PFRs in a range of biochar types and their effects on the growth and oxidative stress of wheat seedlings. Among the biochars prepared by pyrolysis of different types of biomass at 500 °C, the concentrations of PFRs in cow dung and egg shell biochar were the highest and the lowest, respectively. They both increased with artificial weathering treatment but decreased with aging. The dominant types of biochar PFRs were transformed from carbon-centered to oxygen and carbon/oxygen-centered free radicals with weathering. The amount and type of biochar PFRs in mixtures of biochar and soil varied with soil type and biochar dose. After 30 d incubation in different soil-biochar mixtures, measures of wheat plant germination and growth and antioxidant enzyme activity showed increases at lower biochar doses but decreases at higher doses. Catalase activity was 38.1 % greater at 20 g·kg−1 biochar dosage and 25.2 % less at 80 g·kg−1 dosage, on average. In contrast, leaf malondialdehyde content and staining by Evans Blue, both indicators of plant cell membrane damage, generally increased with increasing biochar dosages. Finally, soil hydrolase enzyme activity also displayed an inverted U-shaped dose response. The toxicity indicators showed an increasing trend with higher PFR concentrations in the soil-biochar combinations. While these findings provide evidence for significant potential agricultural and ecological risks associated with the application of biochar due to PFRs damage, it also points to ways that these risks could be mediated such as through biochar dosage restrictions and pre-aging. This study provides new insights into the potential toxicological mechanism and ecological risks associated with the application of biochar in agricultural and environmental settings.

Impact of Biochar Application on Chemical and Microbial Properties of Soil

Biochar is a carbonaceous solid compound formed by high-temperature of organic waste. The quality of biochar produced is determined by pyrolysis conditions and the type of raw materials. This study focused on the evaluation of the impact of biochar application on soil chemical and microbial properties. Four types of biochar from corn cobs, sawdust, mud press, and rice hull were produced and their chemical composition (pH, Organic Matter, Organic Carbon, Total Nitrogen, Carbon: Nitrogen Ratio, Available Phosphorus, and Exchangeable Potassium) was analyzed. A pot experiment with five treatments [T1 - Pure Soil; T2 – Soil + corn cob biochar; T3 – soil + sawdust biochar; T4 – soil + mud press biochar; T5 – soil + rice hull biochar] replicated three times was arranged in a completely randomized design (CRD). An equal amount of soil was placed in pots and mixed with biochar at a ratio of fifty grams (50g) per one-thousand grams (1000g) of soil. A total of fifteen experimental pots were used in the study where each pot contains a soil-biochar mixture of one-thousand five-hundred grams (1500g). Pearson’s correlation coefficients were used to determine how the soils applied with biochar are affected after sixty days of incubation and determine how biochar sources were related. All four biochar from rice hull, corn cobs, mud press, and sawdust are all alkaline and contain comparable amounts of organic matter, organic carbon, pH, soil nitrogen, available phosphorus, and exchangeable potassium. The result of the study showed that biochar application significantly improved soil pH, soil organic matter content, soil organic carbon, and soil nitrogen content. Soils amended with biochar showed comparable amounts of available phosphorus and exchangeable potassium. The application of biochar in soils therefore can be considered a potential solution to enhance soil fertility for sustainable crop production.

Evaluation of coconut biochar as a soil amendment for enhanced productivity of sweet peppers (Capsicum annuum L.) in Joanna, Black Bush Polder, Corentyne, Berbice, Guyana

Agriculture plays a vital role in providing food globally including Guyana, however, the increase in the human population adversely decreases farm size, which results in nutrient depletion on existing farms due to extensive farming activities on the same land season after season. Biochar is commonly used as a non-conventional farming system to enhance the soil’s quality and simultaneously to produce better yield of various staple food crops. Therefore, the purpose of this study was to evaluate the effectiveness of coconut biochar as a soil amendment and to quantify its impact on the growth performance of sweet peppers (Capsicum annuum L.) in Joanna, Black Bush Polder, Corentyne, Berbice, Guyana. A field trial was carried out using the randomized block experimental design with 15 g, 30 g, 45 g biochar; 2 g NPK; and control, each replicated on clayey loam soil. The physico-chemical characteristics of biochar were determined along with the soil-biochar mixture before and after cultivation. In addition, vegetative and reproductive parameters of the sweet peppers, nutrient content of the fruits and chlorophyll content of the leaves were examined. The results obtained from this study revealed that biochar played a minor role in enhancing the yield of the sweet peppers (31.44 g) and amending the soil characteristics when compared to the control. It was observed in this study that soil pH (8.4), organic carbon (1.9 %), carbohydrates concentration (1.25 %) of fruits and chlorophyll content (a:5.6097µM, b: 5.4833 µM, total: 11.093 µM) of the leaves increased with the application of biochar. Based on the obtained results, it can be inferred that biochar may potentially be recommended in the range of 30 g to 45 g as a soil amendment to enhance the growth performance of sweet peppers, however, further experiments with diverse crops and soils are still required to investigate the use of the exact quantity of biochar sourced from different materials.

Simulation of Potassium Availability in the Application of Biochar in Agricultural Soil

Nutrient availability after fertilising agricultural soils is affected by many factors, including soil moisture conditions and physicochemical properties. Herein, the availability of potassium in soil enriched with biochar is studied, considering either saturated or unsaturated moisture conditions and questioning key ion exchange approaches, such as equilibrium exchange (E.E.) and kinetic exchange (K.E.). Potassium release is simulated from a soil–biochar mixture of 0, 0.5, 1 and 2% by coupling HYDRUS-1D and PHREEQC models. The water flow, mass transport and geochemical processes are simulated for a cultivation period that imitates agronomic and environmental conditions of a common agricultural field in Northern Greece. Potassium is released gradually during the irrigation period in the case of unsaturated flow conditions as opposed to its complete release over a few days in the case of saturated flow conditions in the soil. Regarding ion-exchange processes, the soluble amount of potassium is more readily available for transport in soil solution when using the E.E. approach compared to the K.E. approach that assumes a kinetically controlled release due to interactions occurring at the solid–solution interface. The increased proportion of biochar in soil results in a doubling of available potassium. Among the four modelling schemes, although the total mass of potassium released into soil solution is similar, there is a significant variation in release time, indicating that simplified saturated conditions may lead to unrealistic estimates of nutrient availability. Further experimental work will be valuable to decrease the uncertainty of model parameter estimation in the K.E. approach.

Effect of coffee husk and cocoa pods biochar on phosphorus fixation and release processes in acid soils from West Cameroon

AbstractAcid soil in West Cameroon has limited phosphorus (P) availability which limits plant growth. This is mainly because of low pH, high levels of exchangeable aluminium (Al) and iron (Fe) and fixation of P. In this study, acid soils, sampled in Bafang, were amended with biochar produced from coffee husks (CH) and cocoa pod husks (CP) at two different temperatures (350 and 550 °C) in other to evaluate the effect on the physicochemical properties of the acid soil and the effect on P sorption and desorption. The soil was amended with biochar at a rate of 0, 20, 40 and 80 g/kg and incubated for 7 and 60 days. Physicochemical properties of all soil–biochar samples were determined followed by sorption experiments and data fitted in the Langmuir and Freundlich isotherm models in other to evaluate soil P sorption capacity and its affinity to soil amended with biochar. Moreover, desorption studies were done to evaluate the availability of P in soil amended with biochar after sorption. The outcomes of this study reveal an increase in soil pH, electrical conductivity (EC), available P, soil organic carbon and a drastic decrease in exchangeable Al and Fe. The point of zero charge of biochar‐amended soil was higher than the control and increased with amendment rate. The experimental data of the sorption of P on soils and soil–biochar samples fits into Langmuir and Freundlich models (R2 > 0.9) suggesting that the P adsorption is controlled by both model mechanisms. Soil–biochar mixture results in a decrease in the sorption capacity as compared with the control and the decrease was predominant with increasing amendment rate. At amendment rates of 20, 40 and 80 g/kg after 7 days of incubation, for SCH350 were 2267, 2048 and 1823 mg/kg which increased to 2407, 2112 and 1990 mg/kg after 60 days of incubation. This tendency was observed for all biochar inputs with respect to the increase in incubation days. Furthermore, desorption of P from soil–biochar mixtures was enhanced with biochar added at greater rate and produced at higher temperature. The desorption percentage was increased by more than around 10% for all biochar types from 20 mg/kg to 80 mg/kg amendment. Thus, biochar addition to acid soils reduces P fixation to acid soil and improves P desorption to soil solution, thereby providing more available P in the soil solution and better conditions for plant growth.

Embedding of biochar in soil mineral fractions: Evidence from benzene polycarboxylic acids molecular biomarkers

Investigators are debating on the positive and negative priming effects of biochar on native soil organic carbon (SOC), which is largely attributed to the technical barrier of identifying biochar contribution to the apparently measured SOC or mineralized CO2. We combined benzene polycarboxylic acids (BPCAs) molecular biomarkers and soil particle density fractionation to identify biochar contributions to the carbon content in three representative allitic soils in Yunnan. The soil-biochar mixture was incubated for one-month to avoid significant biodegradation of biochar. The results showed that BPCAs were mainly distributed in free light fractions (fLF) up to 87 % of the total BPCAs contents after one month incubation. Recognition of BPCAs in occluded light fractions (oLF) and heavy fractions (HF) suggested a significant interaction between biochar and soil mineral particles. In addition, the percentage of B6CA is comparable or even higher in HF than in fLF or oLF. Thus, biochar-mineral interactions may be an additional stabilization mechanism besides the condensed aromatic structures in biochar. The apparently measured carbon contents increased after biochar application, and both positive and negative priming effects to native SOC were observed after deducting biochar contents based an accurate calculation from BPCAs. The most native SOC depletion (positive priming effects) was noted for the soil with the most favored biochar embedding in soil mineral compositions. This study emphasized that combining BPCAs molecular biomarkers and soil particle density fractionation could accurately quantify different carbon pools, and thus facilitate a comprehensive understanding on the stabilization and turnover of biochar in soils.

Contrasting effects of different field-aged biochars on potential methane oxidation between acidic and saline paddy soils

There is recognition that biochar addition is an appropriate measure to mitigate methane (CH4) emissions by promoting potential methane oxidation (PMO) in the field. However, the mechanism for different field-aged biochars and effective duration after field application are not well documented. Based on a long-term field experiment, biochar was field aged and separated from two contrasting acidic (Ba) and saline (Bs) paddy fields. Then, the effects of different aged biochars on PMO in acidic and saline paddy soils were explored by incubation experiment. There were five treatments for each soil group: soil without biochar (CK), biochar-enriched paddy soil (2 or 6 years) (NB), fresh biochar amendment (Bf), aged biochar separated from acidic paddy soil amendment (Ba), and aged biochar separated from saline paddy soil amendment (Bs). Results showed that saline paddy soils had a significantly higher PMO than acidic paddy soils under treatment without biochar, and that PMO in acidic paddy soil was enhanced by various biochar amendments, whereas those biochar amendments had no significant effects on PMO in saline paddy soil. PMO was positively correlated with pmoA abundance, N consumption rate and pH of soil-biochar mixture. Aged biochar separated from different fields had conflicting influences on soil pH, N consumption rate and PMO. Ba lost its initial effect on changing PMO as compared to Bf treatment when added back into acidic paddy soil. To the contrary, the acidic paddy soil NB treatment containing biochar added six years before possessed the highest value of PMO among all ten treatments. This study suggested that acidic paddy soil with biochar amendment could mitigate CH4 emissions by promoting PMO for a prolonged period, though aged biochar separated from the same field had a limited impact on reducing CH4 emissions.

The effect of biochar from rice husks on evapotranspiration, vegetative growth and fruit yield of greenhouse tomato cultivar anna F1 grown in two soil types

Biochar made from crop residues has been shown to improve soil texture, soil porosity and soil structure. It can enhance fertilizer utilization, reduce leaching loses and hence improve nitrogen supply for plant growth. Utilization of biochar in preparation of potting substrates can enhance growth and yields of greenhouse tomato. A study was carried out to test the influence of rice husks biochar on substrate properties, growth and yield of greenhouse tomato. The experiment was carried as a factorial in completely randomized design with two factors: four biochar levels and two soil types, replicated three times. The biochar levels were volume ratios of 0 biochar: 1 soil (0Biochar), 0.25 biochar: 0.75 soil (0.25Biochar), 0.5 biochar: 0.5 soil (0.5Biochar) and 0.75 biochar: 0.25 soil (0.75Biochar). The two soil types used were the well drained deep red friable soil and imperfectly drained dark brown clay soil obtained from the University farm. Tomato Anna F1 was grown in four-liter plastic pots containing about 3 kg of soil-biochar mixture. Data were collected on the plant growth parameters of plant height, number of leaves per plant and plant dry weight upto the 8th - 9th week after transplanting, when fruit ripening began. The chlorophyll index of the leaves were measured using the SPAD meter. At harvesting, fresh weight and number of the fruits were determined. Incorporating biochar into potting substrate at 0.25-0.75 levels significantly increased evapotranspiration during early vegetative growth. This was indicative of biochar changing substrate properties mainly through significant reduction of bulk density and possibly increasing porosity. Biochar levels of 0.25-0.75 resulted in significant increases in vegetative growth and fruit yield of tomato. Adding biochar to the pot substrate increased tomato plant height, plant dry weight and fruit fresh weight by 21-34%, 50-64% and 49%-56%, respectively. The increase in vegetative growth and fruit yield at 0.25-0.75 biochar levels was attributed to the positive effect of biochar on substrate physical properties. Plant height and number of leaves per plant had a significant linear relationship whose slope, the rate of increase in plant height with increase in number of leaves was not influenced by biochar levels. Biochar enhanced growth without changing the ratio of plant height to number of leaves of tomato. It is concluded that incorporation of biochar made from rice husks at 0.25 level can enhance greenhouse production in both red and clay soils. Key words: Bulk density, Dry weight, Fresh fruit weight, Number of leaves, Plant height

Does biochar affect soil wettability and flow pattern?

Despite the known benefits of biochar application to soils, little is known about its effect on soil wettability and the consequences on soil water movement across the soil profile. Focusing on the latter, three types of commercial biochar derived from wheat, corn, and rice straw produced under low temperature (350–450 ℃) were mixed with a wettable sandy soil at rates of 0%, 2%, 5%, and 10% w/w. Soil water repellency (SWR) of the biochars and biochar–soil mixtures was determined by water drop penetration time (WDPT) test and sessile-drop contact angle (CA) measurement. The WDPT results (< 5 s) showed complete wettability for the biochar–soil mixtures, whereas CA results indicated some water repellency. The mean initial CA of the three biochars varied between 105.3° and 113.9°, with ∼ 30° for the pure sand, and between 56.8° and 75.7° for the biochar–soil mixtures. SWR increased with biochar-application rate, whereas biochar particle size (< 1 mm and > 1 mm) had no significant effects on SWR. A 2-D flow chamber experiment with point source water application at the surface was used to continuously monitor the flow pattern and soil water content (SWC) distribution across the soil profile during infiltration and redistribution periods. Biochar–soil mixtures (2% and 5% w/w) with the three biochar types were studied. Flow chamber results showed substantial differences in plumes shape and internal SWC distribution in the biochar–soil mixtures compared to the untreated sand during the wetting and drainage. The plumes' shape and nonmonotonic spatial SWC distribution suggested unstable flow in the biochar–soil mixtures. The internal fingers developed in the biochar treated sand indicate that SWR induced by biochar addition seemed to be physically induced via the blending of the biochar and soil particles, rather than chemically induced, via coating of the soil particles with amphiphilic molecules. Under field conditions, the primary and inner finger-like plumes may eventually form preferential flow paths that will affect the spatial distribution of water and fertilizer in soil profiles and their availability to plant roots.

Effect of biochar addition on legacy phosphorus availability in long-term cultivated arid soil

BackgroundContinuous application of phosphorus (P) nutrient in association with its low recovery results in large amounts of P being accumulated in soil in different forms. Use of biochar can be a possible means to mobilize soil legacy P and increase its bioavailability. Therefore, the aim of this study was to identify the potential impact of a range of biochar types on P fractions in a long-term cultivated arid soil with high legacy P content.MethodologyThe soil was treated with biochar produced from four feedstock sources (BFS): sewage sludge (SSB), olive mill pomace (OPB), chicken manure (CMB), and date palm residues (DRB) pyrolyzed at 300, 500, or 700 °C in addition to an untreated control. The soil biochar mixture was incubated for 1 month followed by soil P fractionations using sequential chemical extraction to separate soil P into: labile (Resin-Pi, NaHCO3-Pi, NaHCO3-Po), moderately labile (NaOH-Pi, NaOH-Po), and non-labile (HCl-Pi and Residual-P) pools.ResultsBiochar addition clearly influenced most of the soil P fractions; however, the extent of this effect greatly varied depending on BFS and pyrolysis temperature (PT). The most evident biochar impact was observed with labile P pool, with the greatest increase being observed in NaHCO3-Pi fraction in most biochar treatments. Irrespective of PT, SSB and CMB were the most effective biochar type in increasing labile inorganic P; the SSB and CMB increased Resin-Pi by 77 and 206% and NaHCO3-Pi by 200 and 188%, respectively. In contrast, DRB made no changes in any P fraction. Differences in effects of biochar types on labile P is presumably related to the higher content of P in biowaste-based biochar compared to plant-based biochar which have much lower P content. The SSB, CMB, and OPB produced at low temperature reduced HCl-Pi content, indicating that these biochars may have stimulated organic matter decomposition and thereby dissolution of non-labile Ca-associated P to labile P forms.ConclusionOverall, biochar addition appeared to be an effective approach in enhancing legacy P availability in arid soil. However, further studies are necessary to verify these findings in the presence of plant and for a longer period.Graphic abstract

Slow pyrolysis pine wood-derived biochar reduces nitrous oxide production from surface but not subsurface soil

Soil amended with biochar is expected to produce less nitrous oxide (N2O), although this may depend on nitrate (NO3-N) availability. Our objective was to determine how pine wood biochar, slow pyrolyzed at 500 °C, affects N2O production in soil having different denitrification potentials with variable NO3-N concentrations under controlled laboratory conditions. Sandy loam surface soils (0–30 cm, pH 5.7) and sandy clay loam subsurface soils (40–60 cm, pH 5.6) were amended with four biochar rates (0, 10, 20, and 30 g·kg−1), two nitrogen fertilizer rates (0 and 100 mg·kg−1 NO3-N) and two acetylene levels (0% and 10% headspace), arranged as a full factorial. Soil moisture content was adjusted to 80% water-filled pore space, and flasks were incubated at 20 °C for 30 h. Headspace gas was collected from each flask at 25, 26, 28, and 30 h. There was a significant reduction in N2O production with an increasing rate of biochar in the surface soil but not in the subsurface soil. On average, less N2O was produced in the subsurface soil than in the surface soil. As the NO3-N concentration was not a limiting factor for denitrification, the most likely explanation was that denitrifier activity was influenced by the availability of soluble organic carbon in the soil–biochar mixtures. We recommend further study of the coupled carbon–nitrogen transformations during denitrification to understand how biochar influences soil N2O production in sandy loam soils.

Effect of biochar and biochar particle size on plant-available water of sand, silt loam, and clay soil

Biochar is being used as a soil amendment to improve soil hydraulic properties. It has been reported that biochar increases plant-available water, particularly in coarse-textured soils; however, effects on fine-textured soils are less pronounced. Here, we quantified the effects of biochar particle size on plant-available water in sand, silt loam, and clay soils. We amended these soils with a hydrophilic biochar, and packed soil-biochar mixtures into columns of 5.35-cm diameter and 3.0-cm height. Biochar was produced by gasification of woody forest residues. We applied the biochar at two different rates (0.5% and 2% by weight of C) and with four different biochar particle-size fractions (<4.75, <2.0, <1.0 and <0.5 mm). Our results show that biochar amendments increased the plant-available water (when expressed gravimetrically) of all three soils, particularly at the highest biochar application rate. Although the absolute increase in plant-available water was largest for the silt loam soil, the relative increase of plant-available water was greater for the sand than for the silt loam and clay. When expressed in volumetric terms, however, the effects on water retention were less pronounced: the sand showed a small increase in plant-available water with biochar amendment, and no change was observed with the silt loam and clay. Particle size of biochar had little effect on plant-available water (when expressed in gravimetric terms) in the three soils, but silt loam and clay showed increased plant-available water (when expressed in volumetric terms) with decreasing biochar particle size, while no effect was observed for the sand. While our findings corroborate many of the previously reported effects of biochar on soil-water retention, we show that the effects and their magnitude depend on whether the results are reported in terms of gravimetric or volumetric water contents. Because bulk density tends to decrease with increasing biochar application, so will the volumetric water content, and thus the magnitude of the effect on plant-available water will be smaller when expressed in volumetric water content.

Pyrolysis temperature affects pore characteristics of rice straw and canola stalk biochars and biochar-amended soils

Soil physical properties are potentially affected by the addition of biochar. The effect is largely determined by the pore characteristics of biochar, especially the biochar’s feedstocks and pyrolysis processes. This study examined the pore characteristics of rice straw biochars (RSB) and canola stalk biochars (CSB) produced at pyrolysis temperatures of 250, 350, 450, 550, and 650 °C, and evaluated the effects of biochars on soil pore properties. The pore characteristics of biochars were characterized by nitrogen adsorption isotherm (NAI), mercury intrusion porosimetry (MIP), and scanning electron microscope (SEM). Each biochar was mixed into two soils (Ultisol and Alfisol) at the rate of 1% (w/w), then the soil-biochar mixtures were incubated for 90 days. The specific surface area (SSA) and total pore volume (TPV) measured by NAI technique increased with increasing pyrolysis temperature of biochar. Biochars pyrolyzed at 450 °C had the highest porosity and TPV measured by MIP. The largest pore class for RSB was the macropore (>75 μm), while the main pore classes for CSB were micropore (5–30 μm) and ultramicropore (0.1–5 μm). Incubation experimental results showed that biochar addition altered the pore size distribution of the Alfisol and Ultisol. RSB enhanced the total porosity and microporosity of soils, whereas CSB decreased total porosity, macroporosity, and mesoporosity. The water-holding capacity of soil was increased by increasing the amount of soil storage pores caused by biochar. Heatmap analysis on the correlation among pyrolysis temperature of biochar, pore characteristic and water retention capacity of biochar-amended soils illustrated that the pore properties of the Ultisol amended with CSB and the water properties of the Alfisol with CSB were highly correlated with pyrolysis temperature of biochar. Our results suggested the meso- and micro-pores in biochars played an important role to affect the soil response to biochar addition. Based on pore properties, pyrolysis temperature around 450 °C was found to be the optimal condition for producing porous biochar with larger porosity.

Effect of Fine Size-Fractionated Sunflower Husk Biochar on Water Retention Properties of Arable Sandy Soil.

Biochar application has been reported to improve the physical, chemical, and hydrological properties of soil. However, the information about the size fraction composition of the applied biochar as a factor that may have an impact on the properties of soil-biochar mixtures is often underappreciated. Our research shows how sunflower husk biochar (pyrolyzed at 650 °C) can modify the water retention characteristics of arable sandy soil depending on the biochar dose (up to 9.52 wt.%) and particle size (<50 µm, 50–100 µm, 100–250 µm). For comparison, we used soil samples mixed with biochar passed through 2 mm sieve and an unamended reference. The addition of sieved biochar to the soil caused a 30% increase in the available water content (AWC) in comparing to the soil without biochar. However, the most notable improvement (doubling the reference AWC value from 0.078 m3 m−3 to 0.157 m3 m−3) was observed at the lowest doses of biochar (0.95 and 2.24 wt.%) and for the finest size fractions (below 100 µm). The water retention effects on sandy soil are explained as the interplay between the dose, the size of biochar particles, and the porous properties of biochar fractions.

Hydrological Properties of a Clay Loam Soil as Affected by Biochar Application in a Pot Experiment

Improving soil-water relations by amending soil with biochar might play a significant role in increasing water availability for agricultural crops as well as decreasing water loss through drainage or runoff. While the effects of biochar on the hydrological properties on coarse-textured soils are generally positive and well-documented in the literature, studies on biochar effects on fine-textured soils are rather scarce and even contradictory. Therefore, the aim of this paper was to investigate the impact of biochar on the bulk density, water retention curve (together with several water capacitive indicators) and water infiltration rate in a clay loam soil. A pot experiment was carried out under lab conditions in which biochar was mixed with soil at rates of 0 (B0 or control), 2, 4, 6, 8 and 10% dw (B2, B4, B6, B8 and B10, respectively). Water retention of soil–biochar mixtures at different matrix potentials was determined using a pressure plate apparatus. From these measurements, a series of capacitive indicators was derived and the fitting of the van Genuchten model was also performed. Water infiltration into soil–biochar mixtures was measured by means of a mini-disk infiltrometer and the obtained data were analyzed both directly and by fitting the Philip’s model. Biochar significantly affected the considered soil properties. As the biochar rate increased, the bulk density decreased and water retention increased (B6, B8 and B10 &gt; B2, B4 and B0), while the infiltration rate decreased (B0 &gt; B2, B4, B6, B8 and B10). Although the experiment was performed on sieved and repacked soil samples under lab conditions, the results confirmed that biochar has the potential to increase plant-available water, while possibly reducing drainage water in a clay loam soil by lowering the infiltration rate.

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.