Biochar's role in mitigating soil nitrous oxide emissions: A review and meta-analysis

Nitrous oxide (N2O) emissions from soil are an important contributor to global warming, particularly from intensively fertilized croplands. Biochar is commonly applied to reduce N2O emissions and raise soil fertility by regulating soil structure, microbial processes, and crop nitrogen use efficiency. However, the effects of biochar on N2O emissions from fertilized croplands depend on its sources and production conditions, including feedstocks, pyrolysis temperatures, properties and application rates. To generalize findings from individual studies, we synthesized 550 observations that simultaneously measured N2O emissions, nitrification enzyme activity (NEA), denitrification enzyme activity (DEA), and relevant functional genes (AOA, AOB, narG, nirK, nirS, and nosZ) to assess their responses to biochar production conditions, properties and application rates across cropland ecosystems. Wheat straw biochar increased the abundances of all functional genes related to N2O emissions and DEA, while pyrolysis temperatures exceeding 450 ℃ decreased DEA. Low-temperature pyrolysis biochar was particularly effective in reducing N2O emissions. The abundance of denitrifiers and DEA-related genes increased with the pH, ash content, and cation exchange capacity (CEC) of biochar. As biochar application rates increased, N2O emissions were reduced, largely due to an increase in nosZ gene abundance and soil pH. A common biochar application rate of 20 t ha−1 decreased N2O emissions by 19%, primarily through reduced denitrification, while 50 t ha−1 reduced N2O emissions by 48%. Biochar preparation conditions, and property changes had no significant effects on N2O emissions at application rates below 20 t ha−1. When application rates exceeded 20 t ha−1, biochar pyrolysis temperature and properties influenced N2O emissions, indicating a threshold application rate, beyond which biochar affects N2O emissions. Biochar regulates the soil N cycle and N2O emissions primarily through denitrification, with effects dependent on the biochar application rate. These findings underscore the crucial potential of increased biochar application to reduce N2O emissions from fertilized soils globally, thereby contributing to climate change mitigation.Graphical

Annual nitric and nitrous oxide emissions response to biochar amendment from an intensive greenhouse vegetable system in southeast China

ABSTRACTChanges in weather and management practices such as manure and fertilizer applications have a major effect on nitrous oxide (N2O) and nitric oxide (NO) emissions from soils. N2O and NO emissions exhibit high intra- and inter-annual fluctuations, which are also highly influenced by land-use change. In this study we investigated how land-use change between grassland and cornfield affects soil N2O and NO emissions using long-term field measurements in a mollic andosol soil in Southern Hokkaido, Japan. Soil N2O and NO emissions were monitored for 5 years in a 30-year old grassland (OG), which was then plowed and converted to a cornfield for 3 years and then converted back to grassland (new grassland, NG) for another 3 years. We established four treatment plots: control, without any nitrogen (N) input (CT plot); chemical fertilizer only (F plot); chemical fertilizer and manure (MF plot); and manure only (M plot).Changing land use from OG to cornfield increased annual N2O emissions by 6–7 times, while the change from cornfield to NG resulted in a 0.3–0.6 times reduction in annual N2O emissions. N2O emissions in the newly established grassland were 2–5 times higher than those in the 30-year old grassland. Soil mineral N (NO3− and NH4+) was higher in cornfield, followed by NG and lowest in OG, while water extractable organic carbon (WEOC) did not significantly change with changing land use but tended to be higher in OG and NG than in cornfield. The ratio of WEOC to soil NO3− was the most important explanatory variable for differences in N2O emissions as land use changed. High N input, surplus soil N, and precipitation and low soil pH led to increased N2O emissions. N2O emissions in fertilizer- and/or manure-amended plots were 3–4, 2–5 and 1.4–2 times higher than those in the control treatment in OG, cornfield and NG, respectively. NO emissions were largely influenced by soil mineral N and N addition, and showed less response to changing land use. There were high inter-annual variations in both NO and N2O emissions in all plots, including the control treatment, highlighting the need for long-term measurements when determining local emission rates.

A field experiment was conducted in a subtropical tea (Camellia sinensis (L.) O. Kuntze) plantation in Jiangsu Province, China, including the following treatments: no nitrogen (N) fertilizer (control), conventional mineral N fertilizer (urea) (CN), soybean cake fertilizer (SF), pig manure (PM), cattle manure (CaM), chicken manure (CM), and CM + biochar (CMB). Cumulative nitrous oxide (N2O) and nitric oxide (NO) emissions were 4.8 ± 0.1 and 3.7 ± 0.3 kg N ha−1 year−1 under CN, respectively, and increased to 5.4 ± 0.2 and 4.6 ± 0.3 kg N ha−1 year−1 under SF (P < 0.05), respectively. Treatments with livestock manures (PM, CaM, and CM) reduced N2O (41.4–49.6%) and NO (46.5–59.8%) emission in comparison to CN. Combined amendment of CM and biochar more effectively reduced N2O emissions than CM treatment alone. Based on a meta-analysis of 26 global paired measurements in acid soils, the threshold of C/N ratios of organic fertilizers between the positive and negative responses of N2O emissions to organic fertilizers was 8.6 with a range of 4.5–22.3 (95% confidence interval), indicating that reduced N2O emission under PM, CaM and CM was potentially due to their C/N ratios compared to the threshold. Organic fertilizer application did not influence tea yield, while combined application of CM and biochar increased tea yield and resulted in the least yield-scaled N2O emission. N2O and NO emission factors for N fertilizers applied under CN were 1.9 ± 0.1% and 1.5 ± 0.2%, respectively, and reduced to 0.08 ± 0.04% and 0.12 ± 0.04% under CMB, respectively. The results suggest that tea plantations in the subtropical region are hotspots for N2O and NO emissions. Combined application of chicken manure and biochar could mitigate N gas emissions and increase yield in the tea plantation systems.

Biochar decreases soil N2O emissions in Moso bamboo plantations through decreasing labile N concentrations, N-cycling enzyme activities and nitrification/denitrification rates

Tropical soils are important sources of nitrous oxide (N2O) and nitric oxide (NO) emissions from the Earth’s terrestrial ecosystems. Clearing of tropical rainforest for pasture has the potential to alter N2O and NO emissions from soils by altering moisture, nitrogen supply or other factors that control N oxide production. In this review we report annual rates of N2O and NO emissions from forest and pastures of different ages in the western Brazilian Amazon state of Rondonia and examine how forest clearing alters the major controls of N oxide production. Forests had annual N2O emissions of 1.7 to 4.3 kg N ha −1 y −1 and annual NO emissions of 1.4 kg N ha −1 y −1 . Young pastures of 1–3 years old had higher N2O emissions than the original forest (3.1–5.1 kg N ha −1 y −1 ) but older pastures of 6 years or more had lower emissions (0.1 to 0.4 kg N ha −1 y −1 ). Both soil moisture and indices of soil N cycling were relatively poor predictors of N2O, NO and combined N2O + NO emissions. In forest, high N2O emissions occurred at soil moistures above 30% water-filled pore space, while NO emissions occurred at all measured soil moistures (18–43%). In pastures, low N availability led to low N2O and NO emissions across the entire range of soil moistures. Based on these patterns and results of field fertilization experiments, we concluded that: (1) nitrification was the source of NO from forest soils, (2) denitrification was not a major source of N2O production from forest soils or was not limited by NO − supply, (3) denitrification was a major source of N2O production from pasture soils but only when NO − was available, and (4) nitrification was not a major source of NO production in pasture soils. Pulse wettings after prolonged dry periods increased N2O and NO emissions for only short periods and not enough to appreciably affect annual emission rates. We project that Basin-wide, the effect of clearing for pasture in the future will be a small reduction in total N2O emissions if the extensive pastures of the Amazon continue to be managed in a way similar to current practices. In the future, both N2 Oa nd NO fluxes could increase if uses of pastures change to include greater use of N fertilizers or N-fixing crops. Predicting the consequences of these changes for N oxide production will require an understanding of how the processes of nitrification and denitrification interact with soil type and regional moisture regimes to control N2 Oa nd NO production from these new anthropogenic N sources.

All material supplied via Jukuri is protected by copyright and other intellectual property rights. Duplication or sale, in electronic or print form, of any part of the repository collections is prohibited. Making electronic or print copies of the material is permitted only for your own personal use or for educational purposes. For other purposes, this article may be used in accordance with the publisher's terms. There may be differences between this version and the publisher's version. You are advised to cite the publisher's version. This is an electronic reprint of the original article. This reprint may differ from the original in pagination and typographic detail.

Arbuscular mycorrhizal fungi (AMF) establish mutualistic relationships with the majority of terrestrial plants, increasing plant uptake of soil nitrogen (N) in exchange for photosynthates. And may influence soil ammonia (NH3) volatilization and nitrous oxide (N2O) emissions directly by improving plant N uptake, and/or indirectly by modifying soil bacterial community composition for the soil C availability increasing. However, the effects of AMF on soil NH3 volatilization and N2O emissions and their underlying mechanisms remain unclear. We carried out two independent experiments using contrasting methods, one with a compartmental box device (in 2016) and the other with growth pot experiment (in 2020) to examine functional relationships between AMF and soil NH3 volatilization and N2O emissions under varying N input. The presence of AMF significantly reduced soil NH3 volatilization and N2O emissions while enhancing plant biomass and plant N acquisition, and reducing soil NH4+ and NO3-, even with high N input. The presence of AMF also significantly reduced the relative abundance within the bacterial orders Sphingomonadales and Rhizobiales. Sphingomonadales correlated significantly and positively with soil NH3 volatilization in 2016 and N2O emissions, whereas Rhizobiales correlated positively with soil N2O emissions. High N input significantly increased soil NH3 volatilization and N2O emissions with increasing relative abundance of Sphingomonadales and Rhizobiales. These findings demonstrate the contribution of AMF in regulating NH3 and N2O emission by improving plant N uptake and altering soil bacterial communities. They also suggest that altering the rhizosphere microbiome might offer additional potential for restoration of N-enriched agroecosystems.

The responses of nitrous oxide (N2O) emissions to nitrogen (N) application in acidic, perennial agricultural systems, and the factors driving these emissions, remain poorly understood. To address this gap, a 12-year field experiment was conducted to investigate the effects of different N application rates (0, 112.5, 225, and 450 kg N ha−1 yr−1) on N2O emissions, tea yield, and the associated driving factors in a tea plantation. The study found that soil pH significantly decreased with long-term N application, dropping by 0.32 to 0.85 units. Annual tea yield increased significantly, by 148–243%. N application also elevated N2O emission fluxes by 33–277%, with notable seasonal fluctuations observed. N2O flux was positively correlated with N rates, water-filled pore space (WFPS), soil temperature (Tsoil), and inorganic N (NH4+-N and NO3−-N), while showing a negative correlation with soil pH. Random forest (RF) modeling identified WFPS, N rates, and Tsoil as the most important variables influencing N2O flux. The cumulative N2O emissions for N112.5, N225, and N450 were 1584, 2791, and 45,046 g N ha−2, respectively, representing increases of 1.33, 2.34, and 3.77 times compared to N0. The N2O-N emission factors (EF) were 0.35%, 0.71%, and 0.74%, respectively, and increased with higher N rates. These findings highlight the importance of selecting appropriate fertilization timing and improving water and fertilizer management as key strategies for mitigating soil acidification, enhancing nitrogen use efficiency (NUE), and reducing N2O emissions in acidic tea-plantation systems. This study offers a theoretical foundation for developing rational N fertilizer management practices and strategies aimed at reducing N2O emissions in tea-plantation soils.

Organic compounds and mineral nitrogen (N) usually increase nitrous oxide (N2O) emissions. Vinasse, a by‐product of bio‐ethanol production that is rich in carbon, nitrogen, and potassium, is recycled in sugarcane fields as a bio‐fertilizer. Vinasse can contribute significantly to N2O emissions when applied with N in sugarcane plantations, a common practice. However, the biological processes involved in N2O emissions under this management practice are unknown. This study investigated the roles of nitrification and denitrification in N2O emissions from straw‐covered soils amended with different vinasses (CV: concentrated and V: nonconcentrated) before or at the same time as mineral fertilizers at different time points of the sugarcane cycle in two seasons. N2O emissions were evaluated for 90 days, the period that occurs most of the N2O emission from fertilizers; the microbial genes encoding enzymes involved in N2O production (archaeal and bacterial amoA, fungal and bacterial nirK, and bacterial nirS and nosZ), total bacteria, and total fungi were quantified by real‐time PCR. The application of CV and V in conjunction with mineral N resulted in higher N2O emissions than the application of N fertilizer alone. The strategy of vinasse application 30 days before mineral N reduced N2O emissions by 65% for CV, but not for V. Independent of rainy or dry season, the microbial processes were nitrification by ammonia‐oxidizing bacteria (AOB) and archaea and denitrification by bacteria and fungi. The contributions of each process differed and depended on soil moisture, soil pH, and N sources. We concluded that amoA‐AOB was the most important gene related to N2O emissions, which indicates that nitrification by AOB is the main microbial‐driven process linked to N2O emissions in tropical soil. Interestingly, fungal nirK was also significantly correlated with N2O emissions, suggesting that denitrification by fungi contributes to N2O emission in soils receiving straw and vinasse application.

Effect of nitrification and urease inhibitors on nitrous oxide and methane emissions from an oat crop in a volcanic ash soil

Drying and rewetting cycles increased soil carbon dioxide rather than nitrous oxide emissions: A meta-analysis

Improving the management of mineral fertilizers for nitrous oxide mitigation: The effect of nitrogen fertilizer type, urease and nitrification inhibitors in two different textured soils

In order to explore the characteristics of N2O emissions from winter wheat fields in the Loess Plateau under different farming methods and nitrogen levels, the dynamic changes in N2O emissions from rain-fed winter wheat fields were quantified using static box-gas chromatography. Winter wheat 'Xiaoyan22' was used as the material, and a two-factor split area design was adopted. The conventional tillage (CT), straw incorporated into soil (SM), and flat film mulching (FM) were assigned as the main plot, and three nitrogen fertilizer rates (no nitrogen fertilization, 20% nitrogen reduction (144 kg·hm-2), and conventional nitrogen application (180 kg·hm-2)) were assigned as a split plot. Taking CT as a control, the effects of FM and SM on soil N2O emissions under different nitrogen rates were assessed. Furthermore, the correlation between relevant environmental factors and N2O emission flux were analyzed, and N2 emissions were estimated using empirical formulas. The results showed the following:the N2O emissions from the soil of each nitrogen treatment occurred within 20 days, and N2O emission flux peaked within two weeks post-fertilization. The average N2O flux, the total N2O emissions, and the global warming potential of N2O were 1.92-22.75 μg·(m2·h)-1, 0.10-0.46 kg·hm-2, and 26.72-122.15 kg·hm-2, respectively. The N2O emission coefficient of fertilizer nitrogen was 0.05%-0.28%. The total N2 emissions ranged from 0.70-1.82 kg·hm-2. The N fertilization and film mulching significantly increased the N2O emission flux (P<0.05) and the cumulative N2O emissions (P<0.05); however, SM marginally reduced the total N2O emissions. The N2O emission coefficient and global warming potential of fertilizer nitrogen under FM were significantly higher than those under CT and SM (P<0.05). The N2O emissions without nitrogen treatment were only significantly positively correlated with soil water-filled pore spaces (WFPS) (P<0.05); the N2O emissions in the N fertilization condition were significantly positively correlated with WFPS, ω(NO3--N), ω(NH4+-N), and 0-5 cm soil layer temperature (P<0.05). Overall, under the condition of no fertilization, water was the main factor to control the nitrogen transformation and soil N2O emission; nevertheless, under the N fertilization condition, both nitrification and denitrification contributed to the N2O emissions in the rain-fed winter wheat fields. Film mulching practice and nitrogen application markedly increased the N2O emissions, fertilizer nitrogen emission coefficient, and global warming potential in the rain-fed winter wheat fields. Nonetheless, straw incorporated into the soil resulted in a marginal reduction in N2O emissions.

Mitigating N2O and NO Emissions from Direct-Seeded Rice with Nitrification Inhibitor and Urea Deep Placement