Effect of dolomite and biochar addition on N2O and CO2 emissions from acidic tea field soil

Soil pH management for mitigating N2O emissions through nosZ (Clade I and II) gene abundance in rice paddy system

Soil nitrous oxide (N₂O) is produced by abiotic and biotic processes, but it is solely consumed by denitrifying microbes-encoded by nosZ genes. The nosZ gene includes two groups i.e. Clade I and Clade II, which are highly sensitive to pH. Managing pH of acidic soils can substantially influence soil N₂O production or consumption through nosZ gene abundance. Nevertheless, the response of nosZ (Clade I and Clade II) to pH management needs elucidation in acidic soils. To clarify this research question, a pot experiment growing rice crop was conducted with three treatments: control (only soil), low dose of dolomite (LDD), and high dose of dolomite (HDD). The soil pH increased from 5.41 to 6.23 in the control, 6.5 in LDD and 6.8 in HDD treatment under flooded condition. The NH₄⁺ and NO₃^- contents increased and reached the maximum at 30.4 and 21.5 mg kg^-1, respectively, in HDD treatment under flooding condition. The contents of dissolved organic carbon and microbial biomass carbon showed a swift rise at midseason aeration and reached maximum at 30.7 and 101 mg kg^-1 in the HDD treatment. Clade I, Clade II and 16S rRNA genes abundance increased with the onset of flooding, and occurred maximum in the HDD treatment. A peak in N₂O emissions (5.96 μg kg^-1 h^-1) occurred at midseason events in the control when no dolomite was added. Dolomite application significantly (p ≤ 0.001) suppressed N₂O emissions, and HDD treatment was more effective in reducing emissions. Pearson correlation, linear regressions and principal component analysis displayed that increased soil pH and Clade I and Clade II were the main controlling factors for N₂O emission mitigation in acidic soil. This research demonstrates that ameliorating soil acidity with dolomite application is a potential option for the mitigation of N₂O emissions.

Effects of magnesium-modified biochar on soil organic carbon mineralization in citrus orchard

In order to investigate the carbon sequestration potential of biochar on soil, citrus orchard soils with a forest age of 5 years was taken as the research object, citrus peel biochar (OBC) and magnesium-modified citrus peel biochar (OBC-mg) were selected as additive materials, and organic carbon mineralization experiments were carried out in citrus orchard soil. OBC and OBC-Mg were applied to citrus orchard soils at four application rates (0, 1, 2, and 4%), and incubated at a constant temperature for 100 days. Compared with CK, the cumulative mineralization of soil organic carbon decreased by 5.11% with 1% OBC and 2.14% with 1% OBC-Mg. The application of OBC and OBC-Mg significantly increased the content of soil organic carbon fraction, while the content of soil organic carbon fraction was higher in OBC-Mg treated soil than in OBC treated soil. Meanwhile, the cumulative mineralization of soil organic carbon was significantly and positively correlated with the activities of soil catalase, urease and sucrase. The enzyme activities increased with the cumulative mineralization of organic carbon, and the enzyme activities of the OBC-Mg treated soil were significantly higher than those of the OBC treated soil. The results indicated that the OBC-Mg treatment inhibited the organic carbon mineralization in citrus orchard soils and was more favorable to the increase of soil organic carbon fraction. The Mg-modified approach improved the carbon sequestration potential of biochar for citrus orchard soils and provided favorable support for the theory of soil carbon sink in orchards.

Mango performance as affected by the soil application of zeolite and biochar under water salinity stresses

This study was carried out during two consecutive seasons, 2020 and 2021, on 12-year-old mango (Mangifera indica L.). cv. Ewaise grown in region Idku, El Beheira Governorate, Egypt. The trees were planted at 5 × 4 m apart and grafted on "Sokary" root stock to study the influence of zeolite and biochar on growth, yield, and fruit quality of "Ewaise" mango cultivar irrigated by agricultural drainage water. The trees were treated by the following treatments: zeolite or biochar solely at 1, 2, and 3 kg for tree and their different combinations such as 1 kg zeolite + 1 kg biochar; 1 kg zeolite + 2 kg biochar; 1 kg zeolite + 3 kg biochar; 2 kg zeolite + 1 kg biochar; 2 kg zeolite + 2 kg biochar; 2 kg zeolite + 3 kg biochar; 3 kg zeolite + 1 kg biochar; 3 kg zeolite + 2 kg biochar; and 3 kg zeolite + 3 kg biochar as well as control zero soil application. The obtained results showed that the soil application of zeolite or biochar gave a positive effect on improving the soil characteristics which reflects on the tree trunk thickness, shoot length and thickness, number of inflorescences, yield in kg per tree, and fruit quality. The greatest positive effect on the previous mentioned parameters was obtained by the combined application of the soil application of 2 kg zeolite + 3 kg biochar; 2 kg zeolite + 2 kg biochar; 3 kg zeolite + 2 kg biochar; and 3 kg zeolite + 3 kg biochar over the rest-applied treatments or control in the two seasons.

The impact of pristine and modified rice straw biochar on the emission of greenhouse gases from a red acidic soil

With the growing awareness of environmental impacts of land degradation, pressure is mounting to improve the health and productivity of degrading soils, which could be achieved through the use of raw and modified biochar materials. The primary objective of the current study was to investigate the efficiency of pristine and Mg-modified rice-straw biochar (RBC and MRBC) for the reduction of greenhouse gases (GHG) emissions and improvement of soil properties. A 90 days' incubation experiment was conducted using treatments which included control (CK), two RBC dosages (1% and 2.5%), and two MRBC doses (1% and 2.5%). Soil physico-chemical and biological properties were monitored to assess the effects due to the treatments. Results showed that both biochars improved soil physicochemical properties as the rate of biochar increased. The higher rates of biochar (RBC_2.5 and MRBC_2.5) particularly increased enzymatic activities (Catalase, Invertase and Urease) in comparison to the control. Data obtained for phospholipid fatty acid (PLFA) concentration indicated an increase in the Gram-negative bacteria (G-), actinomycetes and total PLFA with the increased biochar rate, while Gram-positive bacteria (G+) showed no changes to either level of biochar. As regards fungi concentration, it decreased with the biochar addition, whereas arbuscular mycorrhizal fungi (AMF) showed non-significant changes. The release of CO₂, CH₄ and N₂O showed a decreasing trend over the time. CO₂ cumulative emission decreased for MRBC₁ (5%) and MRBC_2.5 (9%) over the pristine biochar treatments. The cumulative N₂O emission decreased by 15-32% for RBC₁ and RBC_2.5 and by 22-33% for MRBC₁ and MRBC_2.5 as compared to the control, whereas CH₄ emission showed non-significant changes. Overall, the present study provides for the first-time data that could facilitate the correct use of Mg-modified rice biochar as a soil additive for the mitigation of greenhouse gas emission and improvement of soil properties.

Management Strategies to Mitigate N2O Emissions in Agriculture

The concentration of greenhouse gases (GHGs) in the atmosphere has been increasing since the beginning of the industrial revolution. Nitrous oxide (N2O) is one of the mightiest GHGs, and agriculture is one of the main sources of N2O emissions. In this paper, we reviewed the mechanisms triggering N2O emissions and the role of agricultural practices in their mitigation. The amount of N2O produced from the soil through the combined processes of nitrification and denitrification is profoundly influenced by temperature, moisture, carbon, nitrogen and oxygen contents. These factors can be manipulated to a significant extent through field management practices, influencing N2O emission. The relationships between N2O occurrence and factors regulating it are an important premise for devising mitigation strategies. Here, we evaluated various options in the literature and found that N2O emissions can be effectively reduced by intervening on time and through the method of N supply (30–40%, with peaks up to 80%), tillage and irrigation practices (both in non-univocal way), use of amendments, such as biochar and lime (up to 80%), use of slow-release fertilizers and/or nitrification inhibitors (up to 50%), plant treatment with arbuscular mycorrhizal fungi (up to 75%), appropriate crop rotations and schemes (up to 50%), and integrated nutrient management (in a non-univocal way). In conclusion, acting on N supply (fertilizer type, dose, time, method, etc.) is the most straightforward way to achieve significant N2O reductions without compromising crop yields. However, tuning the rest of crop management (tillage, irrigation, rotation, etc.) to principles of good agricultural practices is also advisable, as it can fetch significant N2O abatement vs. the risk of unexpected rise, which can be incurred by unwary management.

Mitigation of greenhouse gas emissions from a red acidic soil by using magnesium-modified wheat straw biochar

To mitigate greenhouse gas (GHG) emissions, different strategies have been proposed, including application of dolomite, crop straw and biochar, thus contributing to cope with the increasing global warming affecting the planet. In the current study, pristine wheat straw biochar (WBC) and magnesium (MgCl₂.6H₂O) modified wheat straw biochar (MWBC) were used. Treatments included control (CK), two WBC dosages (1% and 2.5%), and two MWBC doses (1% and 2.5%). After 90 days of incubation, WBC and MWBC improved the soil physiochemical properties, being more pronounced with increasing rates of biochar. MWBC_2.5 significantly decreased microbial biomass carbon (MBC), while microbial biomass nitrogen (MBN) increased when both biochar materials (WBC₁ and MWBC₁) were applied at low rate. Compared to control soil, Urease and Alkaline phosphatase activities increased with the increasing rate of WBC and MWBC. The activities of dehydrogenase and β-glucosidase decreased with the WBC and MWBC application, compared to CK. The fluxes of all the three GHGs evaluated (CO₂, CH₄ and N₂O) decreased with time for both biochar amendments, while cumulative emission of CO₂ increased by 58% and 45% for WBC, and by 54% and 41% for MWBC, as compared to CK. The N₂O cumulative emissions decreased by 18 and 34% for WBC, and by 25 and 41% for MWBC, compared to CK, whereas cumulative methane emission showed non-significant differences among all treatments. These findings indicate that Mg-modified wheat straw biochar would be an appropriate management strategy aiding to reduce GHG emissions and improving the physiochemical properties of affected soils, and specifically of the red dry land soil investigated in the current work.

Biochar-induced reduction of N2O emission from East Asian soils under aerobic conditions: Review and data analysis

Global meta-analyses showed that biochar application can reduce N₂O emission. However, no relevant review study is available for East Asian countries which are responsible for 70% of gaseous N losses from croplands globally. This review analyzed data of the biochar-induced N₂O mitigation affected by experimental conditions, including experimental types, biochar types and application rates, soil properties, and chemical forms and application rates of N fertilizer for East Asian countries. The magnitude of biochar-induced N₂O mitigation was evaluated by calculating N₂O reduction index (R_index, percentage reduction of N₂O by biochar relative to control). The R_index was further standardized against biochar application rate by calculating R_index per unit of biochar application rate (ton ha^-1) (Unit R_index). The R_index averaged across different experimental types (n = 196) was -21.1 ± 2.4%. Incubation and pot experiments showed greater R_index than column and field experiments due to higher biochar application rate and shorter experiment duration. Feedstock type and pyrolysis temperature also affected R_index; either bamboo feedstock or pyrolysis at > 400 °C resulted in a greater R_index. The magnitude of R_index also increased with increasing biochar rate. Soil properties did not affect R_index when evaluated across all experimental types, but there was an indication that biochar decreased N₂O emission more at a lower soil moisture level in field experiments. The magnitude of R_index increased with increasing N fertilizer rate up to 500-600 kg N ha^-1, but it decreased thereafter. The Unit R_index averaged across experimental types was -1.2 ± 0.9%, and it was rarely affected by experimental type and conditions but diminished with increasing biochar rate. Our results highlight that since N₂O mitigation by biochar is affected by biochar application rate, R_index needs to be carefully evaluated by standardizing against biochar application rate to suggest the best conditions for biochar usage in East Asia.

Growth, secondary metabolite production, and in vitro antiplasmodial activity of Sonchus arvensis L. callus under dolomite [CaMg(CO3)2] treatment

Malaria is still a global health problem. Plasmodium is a single-cell protozoan parasite that causes malaria and is transmitted to humans through the female Anopheles mosquito. The previous study showed that Sonchus arvensis L. callus has antiplasmodial activity. Several treatments are needed for callus quality improvement for antimalarial compound production. This study aimed to examine the effect of dolomite [CaMg(CO3)2] on growth (morpho-anatomical structure and biomass), secondary metabolite production, and in vitro antiplasmodial activity of S. arvensis L. callus. In this study, leaf explants were grown in Murashige and Skoog medium with a combination of 2,4-dichlorophenoxyacetic acid (2,4-D, one mg/L) and 6-benzyl amino purine (BAP, 0.5 mg/L) with dolomite (50, 75, 100, 150, and 200 mg/L). The 21 days callus ethanolic and methanolic extract were analyzed by gas chromatography-mass spectrometry (GC-MS) and thin-layer chromatography (TLC). The antiplasmodial test was performed on a blood culture infected with Plasmodium falciparum strain 3D7 using the Rieckmann method. The results showed that dolomite significantly affected callus growth, metabolite profile, and in vitro antiplasmodial activity. Dolomite (150 mg/L) showed the highest biomass (0.590 ± 0.136 g fresh weight and 0.074 ± 0.008 g dry weight). GC-MS analysis detected four compounds from callus ethanolic extract. Pelargonic acid, decanoic acid, and hexadecanoic acid were major compounds. One new terpenoid compound is based on TLC analysis. S. arvensis L. callus has antiplasmodial activity with the IC50 value of 5.037 μg/mL. It was three times lower than leaf methanolic extract and five times lower than leaf ethanolic extract.

The contrasting effects of biochar and straw on N2O emissions in the maize season in intensively farmed soil

This study evaluated the combined effects of biochar and straw on N2O flux and the community compositions of nitrifiers and denitrifiers in the maize season in an intensively farmed area in northern China. The experiment consisted of four treatments: (1) CK (only chemical fertilizer application); (2) C (biochar application); (3) SR (straw application to the field); and (4) C+SR (the application of both biochar and straw). The results indicated that during the maize growing season, N2O flux decreased by 30.3% in the C treatment and increased by 13.2% and 37.0% in the SR and C+SR treatments compared with CK, respectively. NO3--N, NH4+-N, and microbial biomass carbon (MBC) were the main soil factors affecting N2O flux, and they were positively correlated with NO3--N and negatively correlated with MBC in the C treatment and positively correlated with NH4+-N in the SR and C+SR treatments. Both biochar addition and straw return shifted the community compositions of nitrifiers and denitrifiers. N2O production was mainly reduced by promoting the ammonia-oxidizing bacteria (AOB) gene abundance and inhibiting the nirK gene abundance in the C treatment but promoted by inhibiting the AOB and nosZ gene abundances in the SR and C+SR treatments. Nitrosospira (AOB) and Rhizobium (nirK) were the main contributors among the treatments. NO3--N, NH4+-N, and MBC were the main soil factors affecting the denitrifier communities. The predominant species associated with the nirK, nirS, and nosZ genes were positively correlated with NO3--N and MBC and negatively correlated with NH4+-N. These results provide valuable information on the mechanism of N2O production and reduction in biochar- and straw-amended soil under field conditions.

Combined application of biochar and nitrogen fertilizer improves rice yield, microbial activity and N-metabolism in a pot experiment

The excessive use of synthetic nitrogen (N) fertilizers in rice (Oryza sativa L.) has resulted in high N loss, soil degradation, and environmental pollution in a changing climate. Soil biochar amendment is proposed as a climate change mitigation tool that supports carbon sequestration and reduces N losses and greenhouse gas (GHG) emissions from the soil. The current study evaluated the impact of four different rates of biochar (B) (C/B₀-0 t ha⁻¹, B₁-20 t ha⁻¹, B₂-40 t ha⁻¹, and B₃-60 t ha⁻¹) and two N levels (N₁; low (270 kg N ha⁻¹) and N₂; high (360 kg N ha⁻¹)), on rice (cultivar Zhenguiai) grown in pots. Significant increases in the average soil microbial biomass N (SMBN) (88%) and carbon (87%) were recorded at the highest rate of 60-ton ha⁻¹B and 360 kg N ha⁻¹ compared to the control (N₁C) during both seasons (S1 and S2). The photochemical efficiency (Fv/Fm), quantum yield of the photosystem (PS) II (ΦPS II), electron transport rate (ETR), and photochemical quenching (qP) were enhanced at low rates of biochar applications (20 to 40 t B ha⁻¹) for high and low N rates across the seasons. Nitrate reductase (NR), glutamine synthetase (GS), and glutamine 2-oxoglutarate aminotransferase (GOGAT) activity were, on average, 39%, 55%, and 63% higher in the N₁B₃, N₂B₂, and N₂B₃ treatments, respectively than the N₁C. The grain quality was higher in the N1B₃ treatment than the N₁C, i.e., the protein content (PC), amylose content (AC), percent brown rice (BRP), and percent milled rice (MRP) were, on average, 16%, 28%, 4.6%, and 5% higher, respectively in both seasons. The results of this study indicated that biochar addition to the soil in combination with N fertilizers increased the dry matter (DM) content, N uptake, and grain yield of rice by 24%, 27%, and 64%, respectively, compared to the N₁C.

The role of biochars in sustainable crop production and soil resiliency

Biochar is a promising soil additive for use in support of sustainable crop production. However, the high level of heterogeneity in biochar properties and the variations in soil composition present significant challenges to the successful uptake of biochar technologies in diverse agricultural soils. An improved understanding of the mechanisms that contribute to biochar-soil interactions is required to address issues related to climate change and cultivation practices. This review summarizes biochar modification approaches (physical, chemical, and biochar-based organic composites) and discusses the potential role of biochar in sustainable crop production and soil resiliency, including the degradation of soil organic matter, the improvement of soil quality, and reductions in greenhouse gas emissions. Biochar design is crucial to successful soil remediation, particularly with regard to issues arising from soil structure and composition related to crop production. Given the wide variety of feedstocks for biochar production and the resultant high surface heterogeneity, greater efforts are required to optimize biochar surface functionality and porosity through appropriate modifications. The design and establishment of these approaches and methods are essential for the future utilization of biochar as an effective soil additive to promote sustainable crop production.

Agro-environmental impacts, carbon sequestration and profit analysis of blended biochar pellet application in the paddy soil-water system

The application of biochar pellet blended with pig manure compost was investigated to estimate its agro-environmental impacts and to evaluate its soil carbon sequestration and profit analysis during rice cultivation. The experiment consisted of four different treatments such as control as pig manure compost only, pig manure compost pellet (PMCP), biochar pellet blended with biochar and pig manure compost (4: 6 ratios, BCP), and slow release fertilizer (SRF). The application of chemical fertilizer and pig manure compost in the whole treatment except the BCP were 90-45-57 kg ha^-1 (N-P-K) and 2600 kg ha^-1, respectively, based on the recommended rates for rice cultivation at National Institute of Agricultural Sciences (NIAS). The BCP and SRF were applied with N 90 kg ha^-1 basis only as basal application before transplanting. The pig manure compost, phosphorous and potassium were applied at basal application while nitrogen fertilizer was applied with three separations as basal and two additional applications. Results showed that concentrations of ammonium nitrogen (NH₄-N) and nitrate nitrogen (NO₃-N) in the BCP at an early stage of rice growth were lowest among the treatments, but their concentrations in the paddy water rapidly decreased at 21 days after transplanting. For paddy soil, NH₄-N concentration in the SRF was continuously high compared to the BCP until 20 days of rice cultivation. For paddy water, phosphate phosphorous (PO₄-P) concentrations in the BCP were three fold lower than the SRF at an early stage of rice growth. Similar pattern between potassium (K) concentrations in paddy water and potassium oxide (K₂O) contents in surface soil was also observed during rice cultivation where their concentrations decreased abruptly 41 days after transplanting. Carbon sequestration and mitigation of carbon dioxide equivalency (CO₂-eq.) emission in the BCP were higher at 1.65 tons ha^-1 and 6.06 tons ha^-1, respectively, than the control while result of its profit analysis was $145.59 (KAU, Korean Allowance Unit) per hectare during rice cultivation. The rice yield were not significantly different (p > 0.05) among all treatments.

Influence of rice-husk biochar and Bacillus pumilus strain TUAT-1 on yield, biomass production, and nutrient uptake in two forage rice genotypes

Biochar is widely used as a soil amendment to increase crop yields. However, the impact of the interaction between the biochar and microbial inoculants (e.g., biofertilizer) on plant nutrient uptake and yield in forage rice is not fully understood. A greenhouse study was conducted to evaluate the synergistic effects of rice-husk biochar and Bacillus pumilus strain TUAT-1 biofertilizer application on growth, yield, and nutrient uptake in two forage rice genotypes; Fukuhibiki and the newly bred line, LTAT-29. Positive effects of biochar and biofertilizer, alone or in a combination, on growth traits, nutrient uptake, and yield components were dependent on the rice genotypes. Biochar and TUAT-1 biofertilizer influenced the overall growth of plants positively and increased straw and above-ground biomass in both genotypes. However, although biochar application significantly increased grain yield in LTAT-29, this was not the case in Fukuhibiki. Biochar and TUAT-1 biofertilizer, either alone or combined, significantly affected plant nutrient uptake but the effect largely depended on rice genotype. Results of this study indicate that biochar amendment and TUAT-1 biofertilizer can enhance forage rice productivity depending on genotypes, and therefore, there is a need to consider plant genetic composition when evaluating the potential for crop response to these soil amendments before application on a commercial scale.

Effects of biochar addition on the NEE and soil organic carbon content of paddy fields under water-saving irrigation

The addition of biochar has been reported as a strategy for improving soil fertility, crop productivity, and carbon sequestration. However, information regarding the effects of biochar on the carbon cycle in paddy fields under water-saving irrigation remains limited. Thus, a field experiment was conducted to investigate the effects of biochar addition on the net ecosystem exchange (NEE) of CO₂ and soil organic carbon (SOC) content of paddy fields under water-saving irrigation in the Taihu Lake region of China. Four treatments were applied: controlled irrigation (CI) without biochar addition as the control (CA), CI with biochar addition at a rate of 20 t·ha^-1 (CB), CI with biochar addition at a rate of 40 t·ha^-1 (CC), and flooding irrigation (FI) with biochar addition at a rate of 40 t·ha^-1 (FC). Biochar addition increased rice yield and irrigation water use efficiency (IWUE) by 24.0-36.3 and 33.4-42.5%, respectively, compared with the control. In addition, biochar addition increased the NEE of CI paddy fields. The average NEE of paddy fields under CB and CC was 2.41 and 30.6% higher than that under CA, respectively. Thus, the increasing effect of biochar addition at a rate of 40 t·ha^-1 was considerably better than those of the other treatments. Apart from biochar addition, irrigation mode was also identified as an influencing factor. CI management increased the NEE of paddy fields by 17.6% compared with FI management. Compared with CA, CB increased total net CO₂ absorption by 10.0%, whereas CC decreased total net CO₂ absorption by 13.8%. Biochar addition also increased SOC, dissolved organic carbon, and microbial biomass carbon contents. Therefore, the joint regulation of biochar addition and water-saving irrigation is a good technique for maintaining rice yield, increasing IWUE, and promoting soil fertility. Furthermore, when amended at the rate of 20 t·ha^-1, biochar addition will be a good strategy for sequestering carbon in paddy fields.

A concise review of biochar application to agricultural soils to improve soil conditions and fight pollution

Application of biochar to soil can play a significant role in the alteration of nutrients dynamics, soil contaminants as well as microbial functions. Therefore, strategic biochar application to soil may provide agronomic, environmental and economic benefits. Key environmental outcomes may include reduced availability of toxic metals and organic pollutants, reduced soil N losses and longer-term storage of carbon in soil. The use of biochar can certainly address key soil agronomic constraints to crop production including Al toxicity, low soil pH and may improve nutrient use efficiency. Biochar application has also demerits to soil properties and attention should be paid when using a specific biochar for a specific soil property improvement. This review provides a concise assessment and addresses impacts of biochar on soil properties.

Aerated Irrigation and Pruning Residue Biochar on N2O Emission, Yield and Ion Uptake of Komatsuna

After irrigation in intensive vegetable cultivation, the soil is filled with water leading to reduced oxygen content of the soil air which will affect vegetable growth and soil N2O emission. In this study, the effect of aerated irrigation and residue biochar on soil N2O emission, yield, and ion uptake of komatsuna grown in Andosol was explored. The experiment included four treatments; control (tap water irrigation), aerated water irrigation, pruning residue biochar with tap water irrigation, and a combination of aerated irrigation and biochar. The results showed that aerated irrigation had no effect on plant growth, but it also increased N2O emission by 12.3% for several days after planting. Plant ion uptake was not affected by aerated irrigation. Biochar amendment increased shoot dry weight and significantly reduced soil N2O emission by 27.9% compared with the control. Plant uptake of N and K also increased with biochar. This study showed that pruning residue biochar has the potential to mitigate N2O emission while increasing vegetable growth and plant nutrient uptake. However, the study soil, Andosol, already has high soil porosity with low bulk density. Thus, further injection of air through irrigation showed no effect on plant growth but increased N2O emission, hence soil aeration was not a limiting factor in Andosol.

Returning Tea Pruning Residue and Its Biochar Had a Contrasting Effect on Soil N2O and CO2 Emissions from Tea Plantation Soil

A laboratory incubation experiment is conducted for 90 days under controlled conditions where either pruning residue or its biochar is applied to determine which application generates the lowest amount of greenhouse gas from tea plantation soil. To study the effect of incorporation depth on soil N2O and CO2 emissions, experiment 1 is performed with three treatments: (1) control; (2) tea pruning residue; and (3) residue biochar mixed with soil from two different depths (0–5 cm and 0–10 cm layers). In experiment 2, only the 0–10 cm soil layer is used to study the effect of surface application of tea pruning residue or its biochar on soil N2O and CO2 emissions compared with the control. The results show that biochar significantly increases soil pH, total C and C/N ratio in both experiments. The addition of pruning residue significantly increases soil total C content, cumulative N2O and CO2 emissions after 90 days of incubation. Converting pruning residue to biochar and its application significantly decreases cumulative N2O emission by 17.7% and 74.2% from the 0–5 cm and 0–10 cm soil layers, respectively, compared to their respective controls. However, biochar addition increases soil CO2 emissions for both the soil layers in experiment 1. Surface application of biochar to soil significantly reduces both N2O and CO2 emissions compared to residue treatment and the control in experiment 2. Our results suggest that converting pruning residue to biochar and its addition to soil has the potential to mitigate soil N2O emissions from tea plantation.

Influence of pruning waste biochar and oyster shell on N2O and CO2 emissions from Japanese pear orchard soil

Two incubation experiments were conducted under controlled moisture and temperature conditions to determine the effects of soil amendment treatments based on pruning waste biochar and oyster shell, on N2O and CO2 emissions from an orchard soil. In experiment 1, four treatments were tested including, control (CK), pruning waste biochar at 2% (B2%), at 10% (B10%), and oyster shell (OS), mixed with soil from two different depths, namely, from the 0-5 cm and the 0-10 cm layers. In experiment 2, only the 0-10 cm soil layer was used to study the effect of surface application of pruning waste biochar (B2% and B10%) on soil N2O and CO2 emissions. The results showed that soil pH, total C and C: N ratio increased with biochar amendment treatments. Significant reduction in soil NO3- content was observed for the B10% treatment. Although OS application increased soil pH, no effect was observed on soil mineral N content, total C or C: N ratio. The rate of N2O emissions from the 0-5 cm soil layer after B2% and B10% addition, significantly declined by 12.5% and 26.3%, respectively. However, only the B10% treatment caused significant reduction in N2O emissions from the 0-10 cm soil layer and from surface soil, by 15.1% and 13.8%, respectively. Oyster shell application had no effect on either soil N2O or CO2 emissions from either soil layer tested. Our results suggest that the addition of pruning waste biochar at a high rate has the potential to mitigate N2O emissions from orchard soils; while, oyster shell can be used for liming without altering soil N2O nor CO2 emissions.