Contrasting effects of biochar on N2O emission and N uptake at different N fertilizer levels on a temperate sandy loam

Insights into CO2 and N2O emissions driven by applying biochar and nitrogen fertilizers in upland soil

Biochar and soil carbon sequestration hold promise in mitigating global warming by storing carbon in the soil. However, the interaction between biochar properties, soil carbon-nitrogen cycling, and nitrogen fertilizer application's impact on soil carbon-nitrogen balance remained unclear. Herein, we conducted batch experiments to study the effects and mechanisms of rice straw biochar application (produced at 300, 500, and 700 °C) on net greenhouse gas emissions (CO2, N2O, CH4) in upland soils under different forms of nitrogen fertilizers. The findings revealed that (NH4)2SO4 and urea significantly elevated soil carbon dioxide equivalent emissions, ranging from 28 to 61.7 kg CO2e/ha and 8.2 to 37.7 kg CO2e/ha, respectively. Conversely, KNO3 reduced soil CO2e emissions, ranging from 2.2 to 13.6 kg CO2e/ha. However, none of these three nitrogen forms exhibited a significant effect on CH4 emissions. The pyrolysis temperature of biochar was found negatively correlated with soil CO2 and N2O emissions. The alkaline substances presented in biochar pyrolyzed at 500-700 °C raised soil pH, increased the ratio of Gram-negative to Gram-positive bacteria, and enhanced the relative abundance of Sphingomonadaceae. Moreover, the co-application of KNO3 based nitrogen fertilizer and biochar increased the total carbon/inorganic nitrogen ratio and reduces the relative abundance of Nitrospirae. This series of reactions led to a significant increase in soil DOC content, meanwhile reduced soil CO2 emissions, and inhibited the nitrification process and decreased the emission of soil N2O. This study provided a scientific basis for the rational application of biochar in soil.

Suitable biochar application practices simultaneously alleviate N2O and NH3 emissions from arable soils: A meta-analysis study

Nitrogen (N) fertilization profoundly improves crop agronomic yield but triggers reactive N (Nr) loss into the environment. Nitrous (N2O) and ammonia (NH3) emissions are the main Nr species that affect climate change and eco-environmental health. Biochar is considered a promising soil amendment, and its efficacy on individual Nr gas emission reduction has been widely reported. However, the interactions and trade-offs between these two Nr species after biochar addition have not been comprehensively analysed. The influencing factors, such as biochar characteristics, environmental conditions, and management measures, remain uncertain. Therefore, 35 publications (145 paired observations) were selected for a meta-analysis to explore the simultaneous mitigation potential of biochar on N2O and NH3 emissions after its application on arable soil. The results showed that biochar application significantly reduced N2O emission by 7.09% while having no significant effect on NH3 volatilisation. Using biochar with a low pH, moderate BET, or pyrolyzed under moderate temperatures could jointly mitigate N2O and NH3 emissions. Additionally, applying biochar to soils with moderate soil organic carbon, high soil total nitrogen, or low cation exchange capacity showed similar responses. The machine-learning model suggested that biochar pH is a dominating moderator of its efficacy in mitigating N2O and NH3 emissions simultaneously. The findings of this study have major implications for biochar application management and aid the further realisation of the multifunctionality of biochar application in agriculture, which could boost agronomic production while lowering environmental costs.

Can the co-application of biochar and different inorganic nitrogen fertilizers repress N2O emissions in acidic soil?

The sole application of nitrogen (N) fertilizer with lower N2O emission potential or combined with biochar may help for mitigating N2O production. However, how biochar applied with various inorganic N fertilizers affected N2O emission in acidic soil remains unclear. Thus, we examined N2O emission, soil N dynamics and relating nitrifiers (i.e., ammonia-oxidizing archaea, AOA) in acidic soil. The study contained three N fertilizers (including NH4Cl, NaNO3, NH4NO3) and two biochar application rates (i.e., 0% and 0.5%). The results indicated that the alone application of NH4Cl produced more N2O. Meanwhile, the co-application of biochar and N fertilizers enhanced N2O emission as well, especially in the combined treatment of biochar and NH4NO3. Soil pH was decreased with the application of various N fertilizers, especially with NH4Cl, and the average decrease rate was 9.6%. Meanwhile, correlation analysis showed a negative relationship between N2O and pH, dramatically, which might indicate that the alteration of pH was one factor relating to N2O emission. However, there was no difference between the same N addition treatments with or without biochar on pH. Interestingly, in the combined treatment of biochar and NH4NO3, the lowest net nitrification rate and net mineralization rate appeared during days 16-23. Meanwhile, the highest emission rate of N2O in the same treatment also appeared during days 16-23. The accordance might indicate that N transformation alteration was another factor relating to N2O emissions. In addition, compared to NH4NO3 alone application, co-applied with biochar had a lower content of Nitrososphaera-AOA, which was a main contributor to nitrification. The study emphasizes the importance of using a suitable form of N fertilizers and further indicates that two factors, namely alteration of pH and N transformation rate, are related to N2O emission. Moreover, in future studies, it is necessary to explore the soil N dynamics controlled by microorganisms.

Inhibitors mitigate N2O emissions more effectively than biochar: A global perspective

Farmlands receive large amounts of nitrogen (N) from anthropogenic activities, which increase N₂O emissions and promote crop productivity. Inhibitor or biochar applications have proven effective in reducing N₂O emissions and promoting crop yields worldwide. However, a direct comparison of the response of N₂O emissions and crop yields to inhibitor and biochar applications has not been performed. Here, we conducted a meta-analysis of 787 datasets from different locations worldwide to investigate the response of N₂O emissions and crop yields to inhibitor or biochar applications for different climate factors and experimental conditions and determine the key influencing factors. We found that inhibitor applications (37.4 %) resulted in larger N₂O emission reductions than biochar applications (20.2 %), but there was no difference in the crop yield improvement (5.8 % and 5.4 %, respectively). Nitrification inhibitor (NI) applications reduced N₂O emissions by 40.8 %, a larger reduction than that of urease inhibitor (UI) applications (24.3 %) and the combination of NI and UI applications (36.4 %); 3,4-dimethylpyrazole succinic (DMPSA) was the most effective NI in reducing N₂O emissions (50.7 %). We also found that NI applications were more effective in reducing N₂O emissions than biochar applications in different climates and experimental conditions (N source, N rate, cropland type, and soil texture). In addition, the N rate was the most important factor impacting N₂O emissions and crop yields when inhibitors were applied, whereas the experimental duration had the largest influence on N₂O emissions under biochar applications. Moreover, soil factors were also related to N₂O emissions under biochar applications or inhibitor applications. Our findings indicate that inhibitors are more effective in reducing N₂O emissions than biochar worldwide.

Combined effects of biochar and biogas slurry on soil nitrogen transformation rates and N2O emission in a subtropical poplar plantation

It has been widely accepted that biochar has a great potential of mitigating soil nitrous oxide (N₂O) emission. However, the underlying mechanism about how biochar affects nitrogen transformation and the pathways of soil N₂O production is under discussion. A ¹⁵N-tracer incubation experiment was conducted to investigate the short-term effects of biochar on soil N transformation rates and source partitioning of N₂O emissions in soils from a poplar plantation system. A two-factor experimental design was adopted using biogas digestate slurry and biochar as soil amendments. In total, there were 12 treatments, including three rates of biochar: B0 (control), B2 (80 t ha^-1), and B3 (120 t ha^-1), and four rates of biogas digestate slurry: C (0 m³ ha^-1), L (125 m³ ha^-1), M (250 m³ ha^-1), and H (375 m³ ha^-1). We observed significantly lower rates of net nitrification (N_n) and mineralization (M_n) in biochar-treated soils. The ¹⁵N tracer analysis revealed a significant decrease in gross autotrophic (O_NH4), heterotrophic nitrification (O_Nrec), and mineralization (M_Norg) rates while an increase in gross immobilization (I_NH4 and I_NO3) rates in biochar amended soils. When biogas slurry was applied, biochar only significantly reduced O_NH4 except in the moderate slurry treatment. Regardless of the slurry application, biochar consistently suppressed N₂O emission by 58-89 %, and nitrification was the dominant pathway accounting contributing >90 % to cumulative N₂O emissions. Moreover, soil cumulative N₂O emissions significantly negatively correlated with soil ammonium contents and positively with M_Norg, M_n, and N_n, showing that biochar decreased N₂O emission via a reducing effect on nitrification rates and associated N₂O emissions. Our results also highlight that application of N fertilizer greatly influence the biochar's impacts on soil N transformation rates and N₂O emission, calling for further studies on their interactions to develop mitigate options and to improve N use efficiency.

Biochar derived from spent mushroom substrate reduced N2O emissions with lower water content but increased CH4 emissions under flooded condition from fertilized soils in Camellia oleifera plantations

Agricultural soils are major sources of greenhouse gases (GHGs) that related with intensive fertilizer input. Biochar is widely used to mitigate GHGs, which may interact with soil water content impacting GHG emissions. Camellia oleifera fruit shell (FS) and spent mushroom substrate (MS) are ideal biochar feedstocks. However, the impact of water content and biochar on soil GHG emissions has not been thoroughly understood. Here, we examined CH₄ and N₂O emissions from C. oleifera plantation soils as affected by biochar (derived from MS or FS, 1 g 25 g^-1 soil), water content (60%, 120%, 240% or 360% water holding capacity, WHC), and fertilization (control or chicken manure, CM 2.5 g 25 g^-1 soil). We determined the abundance of related microbial functional genes to obtain the underlining mechanisms. The results showed that higher N₂O emissions occurred in soils with 120%WHC, due to increased abundance of AOA, AOB and nirS. MS or FS biochar differed in their effects on soil GHG emissions with different WHC. MS biochar was higher in pH, C/N and specific surface area, and mitigated more N₂O emissions from soils with CM and 120%WHC relative to FS biochar (by 92.9% and 34.6%, respectively). MS biochar significantly decreased abundance of nitrification related functional genes (AOA, AOB) in soils with 120%WHC and CM, which explained the decrease in N₂O emissions. However, MS biochar increased cumulative CH₄ emissions from flooded soils via increase in mcrA abundance. Thereby, biochar feedstocks should be considered in CH₄ and N₂O mitigations from soils with different water contents.

Combined biochar and double inhibitor application offsets NH3 and N2O emissions and mitigates N leaching in paddy fields

The effects of combined biochar and double inhibitor application on gaseous nitrogen (N; nitrous oxide [N₂O] and ammonia [NH₃]) emissions and N leaching in paddy soils remain unclear. We investigated the effects of biochar application at different rates and double inhibitor application (hydroquinone [HQ] and dicyandiamide [DCD]) on NH₃ and N₂O emissions, N leaching, as well as rice yield in a paddy field, with eight treatments, including conventional urea N application at 280 kg N ha^-1 (CN); reduced N application at 240 kg N ha^-1 (RN); RN + 7.5 t ha^-1 biochar (RNB1); RN + 15 t ha^-1 biochar (RNB2); RN + HQ + DCD (RNI); RNB1 + HQ + DCD (RNIB1); RNB2 + HQ + DCD (RNIB2); and a control without N fertilizer. When compared with N leaching under RN, biochar application reduced total N leaching by 26.9-34.8% but stimulated NH₃ emissions by 13.2-27.1%, mainly because of enhanced floodwater and soil NH₄⁺-N concentrations and pH, and increased N₂O emission by 7.7-21.2%, potentially due to increased soil NO₃^--N concentrations. Urease and nitrification inhibitor addition decreased NH₃ and N₂O emissions, and total N leaching by 20.1%, 21.5%, and 22.1%, respectively. Compared with RN, combined biochar (7.5 t ha^-1) and double inhibitor application decreased NH₃ and N₂O emissions, with reductions of 24.3% and 14.6%, respectively, and reduced total N leaching by up to 45.4%. Biochar application alone or combined with double inhibitors enhanced N use efficiency from 26.2% (RN) to 44.7% (RNIB2). Conversely, double inhibitor application alone or combined with biochar enhanced rice yield and reduced yield-scaled N₂O emissions. Our results suggest that double inhibitor application alone or combined with 7.5 t ha^-1 biochar is an effective practice to mitigate NH₃ and N₂O emission and N leaching in paddy fields.

Incapability of biochar to mitigate biogas slurry induced N2O emissions: Field investigations after 7 years of biochar application in a poplar plantation

Nitrous oxide (N₂O) is a potent atmospheric greenhouse gas that is largely emitted from soils due to the enhanced use of reactive nitrogen in agriculture and plantations. In this study, we evaluated the N₂O mitigation ability of biochar after 7 years of application in a poplar plantation. The field experiment was based on combinations of three biochar (0, 80, and 120 t ha^-1) and four biogas slurry (0, 125, 250, and 375 m³ ha^-1) rates following a factorial design. N₂O flux rates were measured for seven consecutive months using in situ static chambers. Soil physicochemical characteristics, potential nitrification rate (PNR), denitrification (DEA), and N₂O reduction were recorded once each in September 2019 and January 2020 via lab incubations. In addition, qPCR assays were used to assess the abundance of key nitrifying and denitrifying functional genes. Biochar application after 7 years had no significant effects on N₂O flux rates, PNR, and DEA rates. However, a triggering effect of biogas slurry on soil N₂O emission was observed, although there was no correlation between biogas slurry rates and N₂O emission rates. Factorial ANOVA showed a significant effect of biogas slurry and its interaction with biochar on the relative abundance of bacterial denitrifying and nitrifying functional genes. Additionally, significant correlations of N₂O emission rates with PNR rates and NO₃^- concentration indicated that nitrification was the dominant pathway of N₂O emission. Thus, a single biochar application did not mitigate N₂O emission rates induced by biogas slurry on a long-term scale.

Effect and mechanism of biochar on CO2 and N2O emissions under different nitrogen fertilization gradient from an acidic soil

"Nature based solutions" has been proposed at COP25 as an important venture for combating anthropogenic climate change, and soil biochar amendment have been proposed to have vast carbon sequestration potential. On the other hand, biochar carbon storage in soils is confronted with both biochar and soil carbon and nitrogen loss. The superposition of these two influences leads to complex variation in net greenhouse gas emissions from biochar-amended-soils. Nitrogen fertilization is a common agriculture practice in China and worldwide. To study the effects and mechanisms of biochar on soil net greenhouse gas emissions (CO₂, N₂O) under different nitrogen fertilization gradient in a ferrallitic soil, a soil column experiment was conducted. Maize straw derived biochar (pyrolysed at 500 °C) and nitrogen fertilizer (ammonium sulfate) were investigated at varying application rates. It was found that biochar amendment increased CO₂ emissions by 51.1%-57.1% and N₂O emissions by 50.0%-73.7%, respectively, when soil was incubated with 50 mg N/kg nitrogen fertilization. The N₂O emission in soil was dominated by nitrification, and the labile fraction of biochar played the dominant role in increasing soil CO₂ and N₂O emissions. Therefore, water or acid washing of biochar before its application would significantly reduce the net GHG emissions. When the nitrogen fertilization was applied at the unusually high level of 450 mg N/kg, the N₂O emissions mainly came from denitrification. Biochar amendment introduced less soil CO₂ emission increment, and suppressed N₂O emissions by inhibition of denitrification via adsorption protection mechanism (towards nitrogen) and aeration effect. A chain mechanism has been illustrated and results from this study suggest that biochar is best applied to an environment or the circumstance that maximizes adsorption protection mechanism and aeration effect to achieve total greenhouse gas emission reduction. This study therefore provides basis for the scientific sound application and regulation of biochar amendment in soils.

Biochar prepared at different pyrolysis temperatures affects urea-nitrogen immobilization and N2O emissions in paddy fields

Background

Food safety has become a major issue, with serious environmental pollution resulting from losses of nitrogen (N) fertilizers. N is a key element for plant growth and is often one of the most important yield-limiting nutrients in paddy soil. Urea-N immobilization is an important process for restoring the levels of soil nutrient depleted by rice production and sustaining productivity. The benefits of biochar application include improved soil fertility, altered N dynamics, and reduced nutrient leaching. However, due to high variability in the quality of biochar, the responses of N loss and rice productivity to biochar amendments, especially those prepared at different pyrolysis temperatures, are still unclear. The main objectives of the present study were to examine the effects of biochar prepared at different pyrolysis temperatures on fertilizer N immobilization in paddy soil and explore the underlying mechanisms.

Methods

Two biochar samples were prepared by pyrolysis of maize straw at 400 °C (B400) and 700 °C (B700), respectively. The biochar was applied to paddy soil at three rates (0, 0.7, and 2.1%, w/w), with or without N fertilization (0, 168, and 210 kg N ha^–1). Pot experiments were performed to determine nitrous oxide (N₂O) emissions and ¹⁵N recovery from paddy soil using a ¹⁵N tracer across the rice growing season.

Results

Compared with the non-biochar control, biochar significantly decreased soil bulk density while increasing soil porosity, irrespective of pyrolysis temperature and N fertilizer level. Under B400 and B700, a high biochar rate decreased N loss rate to 66.42 and 68.90%, whereas a high N level increased it to 77.21 and 76.99%, respectively. Biochar also markedly decreased N₂O emissions to 1.06 (B400) and 0.75 kg ha⁻¹ (B700); low-N treatment caused a decrease in N₂O emissions under B400, but this decrease was not observed under B700. An application rate of biochar of 2.1% plus 210 kg ha⁻¹ N fertilizer substantially decreased the N fertilizer-induced N₂O emission factor under B400, whereas under B700 no significant difference was observed. Biochar combined with N fertilizer treatment decreased rice biomass and grain yield by an average of 51.55 and 23.90 g pot^–1, respectively, but the yield reduction under B700 was lower than under B400.

Conclusion

Irrespective of pyrolysis temperature, biochar had a positive effect on residual soil ¹⁵N content, while it negatively affected the ¹⁵N recovery of rice, N₂O emissions from soil, rice biomass, and grain yield in the first year. Generally, a high application rate of biochar prepared at high or low pyrolysis temperature reduced the N fertilizer-induced N₂O emission factor considerably. These biochar effects were dependent on N fertilizer level, biochar application rate, and their interactions.

Effect of biochar origin and soil type on the greenhouse gas emission and the bacterial community structure in N fertilised acidic sandy and alkaline clay soil

Soil amendment with biochar has received increased attention because of its potential to i) sequester carbon and ii) reduce N₂O emission when applied to N fertilised soils. To study the effect of biochar origin on greenhouse gas emission in two contrasting soil types, we used a robotized continuous flow incubation system and δ¹³C stable isotope approach to compare four biochar types (feed stock: olive mill, corn cob, pistachio shell, cotton stalk) in an alkaline clay soil and two selected biochar types (feed stock: olive mill and corn cob) in an acidic sandy soil. Furthermore, high-throughput sequencing of 16S rRNA genes was performed at the end of the incubation to investigate the effect of different biochars on bacterial community structure in the two different soils. In the alkaline clay soil, all biochar types in conjunction with N fertiliser decreased CO₂ emissions up to 12% compared to the N added control treatment causing negative priming, whereas no significant effect of biochar addition on N₂O emissions was observed. In contrast, application of olive mill biochar to the acidic sandy soil significantly increased soil pH, CO₂, and N₂O fluxes, whereas no significant effect of corn cob biochar addition was observed. There was a significant linear relationship between the biochar induced increase in soil pH and the biochar induced increase in soil born N₂O emission. Additionally, we detected a clear variation in bacterial community structure in the acidic sandy soil (phyla Acidobacteria, Nitrospirare, and Arthrobacter) with the olive mill biochar addition. Overall, the amendment of different biochars failed to mitigate N₂O emissions in both soil types when mineral fertiliser was added. Furthermore, amendment of olive mill biochar stimulated both N₂O and CO₂ emissions in the low pH sandy soil and altered the bacterial community structure, which was possibly related to its liming effect.

Effects of arbuscular mycorrhizal fungi, biochar and cadmium on the yield and element uptake of Medicago sativa

The synergistic effects of arbuscular mycorrhizal fungi (AMF) inoculation and biochar application on plant growth and heavy metal uptake remain unclear. A pot experiment was carried out to investigate the influence of AMF inoculation, biochar and cadmium (Cd) addition on the growth, nutrient and cadmium uptake of Medicago sativa, as well as soil biological and chemical characteristics. In comparison to the non-Cd pollution treatment, Cd addition significantly decreased mycorrhizal colonization, biomass, and N, P, Ca and Mg contents of shoots and roots in the absence of biochar. Biochar amendment did not increase mycorrhizal colonization at either Cd levels. Regardless of the biochar amendment, AMF inoculation significantly promoted contents of N and P in plant shoots grown in the Cd-contaminated soils. Nevertheless, in the presence of Cd pollution, biochar dramatically elevated the biomass and N, P, K and Ca contents of plant tissues in both AMF inoculation treatments. Biochar addition significantly reduced soil DTPA-extracted Cd. The treatments with AMF inoculation and biochar amendment showed the lowest shoot Cd concentrations and contents, highest plant tissue N and P contents in the Cd addition group. These results suggested that combined use of AMF inoculation and biochar amendment had significant synergistic effects not only on nutrient uptake but also on the reduction in cadmium uptake of alfalfa grown in Cd-polluted soil.

Separated pathways for biochar to affect soil N2O emission under different moisture contents

Dry land is a massive contributor to global nitrous oxide (N₂O) production and biochar is a potential material for soil amendment that can impact soil N₂O emission. Considering that the moisture content of dry land is usually changeable, it is essential to investigate the effect of biochar on soil N₂O emission under different moisture contents. Therefore, column experiments were conducted with two biochars (B300 and B500, biochars pyrolyzed at 300 and 500 °C, respectively) under five moisture contents (18%, 21%, 24%, 27% and 30%, w/w). The results showed that B300 promoted N₂O emission under the moisture contents of 18%, 21% and 24% by increasing the content of dissolved organic carbon and thus enhancing the microbial processes related to N₂O production. However, when the moisture contents were 27% and 30%, the promotion of N₂O production was overwhelmed by the improvement in N₂O reduction due to the B300 induced increase in the abundance ratio of nosZ to nirS, leading to the decrease in N₂O emission. Moreover, B500 did not alter the content of dissolved organic matter significantly and thus caused no significant change in N₂O emission when the moisture contents were 18%, 21% and 24%. But it was able to increase the abundance ratio of nosZ to nirS and thus decrease N₂O emission when the moisture contents were 27% and 30%. The results further clarified the effect of biochar on soil N₂O emission and helped to evaluate the N₂O-suppressing-potential of biochar.

Degradability of raw and post-processed chars in a two-year field experiment

The object of the present work was to analyse the degradation dynamics of four chars and a digestate applied to a sandy soil as well as possible initial priming effects on the mineralisation of soil organic carbon in a two-year field experiment. For that purpose, soil carbon content, soil respiration and the corresponding carbon isotopic abundances were repeatedly measured throughout two consecutive vegetation periods. In order to quantify and separate the amount and the degradation of the substrate-derived carbon and to assess soil priming effects, isotopic mixing models were applied to soil-derived and substrate-derived carbon, and to the respired CO₂. Pyrolysis char was degraded with decreasing intensity over time with an estimated half-life of about 80years. HTC (HydroThermal Carbonisation) char showed a high degradation during the first year but, during the second year, the remaining recalcitrant pool was degraded much slower with a half-life between 49 and 61years. Digestate was degraded at a constant intensity with a half-life of about 14years. When the chars were fermented before being applied to the soil, the initial degradation of HTC char was reduced, but on the two-year scale, the degradation of both chars was higher than for untreated chars, yielding a half-life between 11 and 15years, comparable to digestate. The results showed considerable stability of the untreated pyrolysis and HTC chars under field conditions, and moreover, no net influence of chars as well as of digestate on the degradation of soil organic carbon after two years.

Offsetting global warming-induced elevated greenhouse gas emissions from an arable soil by biochar application

Global warming will likely enhance greenhouse gas (GHG) emissions from soils. Due to its slow decomposability, biochar is widely recognized as effective in long-term soil carbon (C) sequestration and in mitigation of soil GHG emissions. In a long-term soil warming experiment (+2.5 °C, since July 2008) we studied the effect of applying high-temperature Miscanthus biochar (0, 30 t/ha, since August 2013) on GHG emissions and their global warming potential (GWP) during 2 years in a temperate agroecosystem. Crop growth, physical and chemical soil properties, temperature sensitivity of soil respiration (R_s ), and metabolic quotient (qCO₂ ) were investigated to yield further information about single effects of soil warming and biochar as well as on their interactions. Soil warming increased total CO₂ emissions by 28% over 2 years. The effect of warming on soil respiration did not level off as has often been observed in less intensively managed ecosystems. However, the temperature sensitivity of soil respiration was not affected by warming. Overall, biochar had no effect on most of the measured parameters, suggesting its high degradation stability and its low influence on microbial C cycling even under elevated soil temperatures. In contrast, biochar × warming interactions led to higher total N₂ O emissions, possibly due to accelerated N-cycling at elevated soil temperature and to biochar-induced changes in soil properties and environmental conditions. Methane uptake was not affected by soil warming or biochar. The incorporation of biochar-C into soil was estimated to offset warming-induced elevated GHG emissions for 25 years. Our results highlight the suitability of biochar for C sequestration in cultivated temperate agricultural soil under a future elevated temperature. However, the increased N₂ O emissions under warming limit the GHG mitigation potential of biochar.

Efficacies of biochar and biochar-based amendment on vegetable yield and nitrogen utilization in four consecutive planting seasons

Biochar has been suggested as a potential tailored technology for mediating soil conditions and improving crop yields. However, the efficacies of biochar and biochar-based amendments (e.g., composted biochar) in agricultural soils under a rotation system remain uncertain. In this study, an arable soil was subjected to peanut shell biochar (PBC) and biochar-based amendment (PAD) combined with or without nitrogen (N) fertilizer to evaluate their effects on vegetable yield, N bioavailability, and their relative contribution to vegetable biomass in four consecutive planting seasons. PBC alone or in co-application with N fertilizer had little effect on vegetable yield, while PAD co-application with N fertilizer decreased vegetable biomass because of the inhibition of root morphology by excessive nutrient supply. PBC and PAD applications increased rhizosphere soil pH due to OH^- and HCO₃^- release and NO₃^--N uptake. Although the addition of PAD increased soil N contents due to its high contents in PAD, it had little effects on N utilization efficiency (NUE) in the four seasons. The relative contribution of PBC, PAD, and their interaction with N fertilizer to biomass yield was maintained at a low level. Our results indicated that a biochar-based amendment (e.g., PAD) was a potential alternative to N fertilizer, but the ratio of biochar to additives should be managed carefully to generate optimal benefits. Notably, the efficacy of PAD on plant growth was closely associated with plant species, and further related research on different plants is encouraged.