Nitrous oxide flux from komatsuna (Brassica rapa) vegetated soil: a comparison between biogas digested liquid and chemical fertilizer

Biogas production generates digested slurry as a by-product. It can be used as fertilizer especially after its conversion into digested liquid. A microcosm-based study was conducted in order to compare the effects of single application of digested liquid or chemical fertilizer on N₂O flux and crop yield of komatsuna vegetable. Analysis revealed that digested liquid-treated soils released almost equal cumulative N₂O (0.43 g?N m^?2) compared to chemical fertilizer (0.39 g?N m^?2). The uncropped soils treated with the digested liquid and chemical fertilizer released more N₂O compared to corresponding cropped soils. The N₂O emission factor and soil mineral N contents were similar for the digested liquid and chemical fertilizer-treated soils. Plant biomass in the first crop after digested liquid application was significantly higher (5.59 g plant^?1) than that after applied chemical fertilizer (4.78 g plant^?1); but there was no significant difference for the second crop. Nitrogen agronomic efficiency was improved by the digested liquid compared to chemical fertilizer. This study indicates that cumulative N₂O flux was similar after application of the digested liquid and chemical fertilizer, while the overall yield from both croppings was increased in the digested liquid-treated soil compared to chemical fertilizer-treated soil.     

Application of biochar to soil and N2O emissions: potential effects of blending fast‐pyrolysis biochar with anaerobically digested slurry

Soil applications of recalcitrant biochar offer the possibility of mitigating climate change effects through long‐term carbon sequestration and potentially also by reducing emissions of the potent greenhouse gas nitrous oxide (N₂O). This laboratory study examined the effect of combining a fast‐pyrolysis biochar at small (1% by mass) and large (3%) concentrations with anaerobically digested slurry on soil N₂O and carbon dioxide (CO₂) emissions over a period of 55 days. The results showed that fast‐pyrolysis biochar applied on its own increased N₂O emissions from soil. However, when biochar was applied together with slurry, the larger biochar concentration decreased N₂O emissions by 47%, relative to those from the slurry treatment with the smaller biochar concentration. Reduced N₂O emissions coincided with enhanced soil microbial activity and immobilization of nitrogen. A combined application of biochar and anaerobic digested slurry could therefore be beneficial for cropping systems in terms of soil nitrogen retention while concurrently mitigating N₂O fluxes and sequestering carbon in soil.     

Effects of biochar addition on N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions from two paddy soils

Impacts of biochar addition on nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from paddy soils are not well documented. Here, we have hypothesized that N₂O emissions from paddy soils could be depressed by biochar incorporation during the upland crop season without any effect on CO₂ emissions. Therefore, we have carried out the 60-day aerobic incubation experiment to investigate the influences of rice husk biochar incorporation (50 t ha⁻¹) into two typical paddy soils with or without nitrogen (N) fertilizer on N₂O and CO₂ evolution from soil. Biochar addition significantly decreased N₂O emissions during the 60-day period by 73.1% as an average value while the inhibition ranged from 51.4% to 93.5% (P < 0.05–0.01) in terms of cumulative emissions. Significant interactions were observed between biochar, N fertilizer, and soil type indicating that the effect of biochar addition on N₂O emissions was influenced by soil type. Moreover, biochar addition did not increase CO₂ emissions from both paddy soils (P > 0.05) in terms of cumulative emissions. Therefore, biochar can be added to paddy fields during the upland crop growing season to mitigate N₂O evolution and thus global warming.     

Wheat straw and its biochar had contrasting effects on soil C and N cycling two growing seasons after addition to a Black Chernozemic soil planted to barley

Application of crop residues and its biochar produced through slow pyrolysis can potentially increase carbon (C) sequestration in agricultural production systems. The impact of crop residue and its biochar addition on greenhouse gas emission rates and the associated changes of soil gross N transformation rates in agricultural soils are poorly understood. We evaluated the effect of wheat straw and its biochar applied to a Black Chernozemic soil planted to barley, two growing seasons or 15 months (at the full-bloom stage of barley in the second growing season) after their field application, on CO₂ and N₂O emission rates, soil inorganic N and soil gross N transformation rates in a laboratory incubation experiment. Gross N transformation rates were studied using the ¹⁵N isotope pool dilution method. The field experiment included four treatments: control, addition of wheat straw (30 t ha^?1), addition of biochar pyrolyzed from wheat straw (20 t ha^?1), and addition of wheat straw plus its biochar (30 t ha^?1 wheat straw + 20 t ha^?1 biochar). Fifteen months after their application, wheat straw and its biochar addition increased soil total organic C concentrations (p?=?0.039 and <0.001, respectively) but did not affect soil dissolved organic C, total N and NH₄ ⁺-N concentrations, and soil pH. Biochar addition increased soil NO₃ ^?-N concentrations (p?=?0.004). Soil CO₂ and N₂O emission rates were increased by 40 (p?p?=?0.03), respectively, after wheat straw addition, but were not affected by biochar application. Straw and its biochar addition did not affect gross and net N mineralization rates or net nitrification rates. However, biochar addition doubled gross nitrification rates relative to the control (p?2 and N₂O emissions and enhance soil C sequestration. However, the implications of the increased soil gross nitrification rate and NO₃ ^?-N in the biochar addition treatment for long-term NO₃ ^?-N dynamics and N₂O emissions need to be further studied.     

生物炭施用下中国农田土壤N2O排放的Meta分析

为明确施加生物炭对中国农田土壤N_2O排放的影响和主要控制因素,以公开发表的试验数据为研究对象,采用Meta-analysis法定量分析了施加生物炭条件下,气候、土壤性质、田间管理方式、生物炭性质与施加量对土壤N_2O排放的影响,并对各影响因素进行通径分析。结果表明,当年降雨量≥600 mm时,生物炭显著降低土壤N_2O排放量(P0.05),且随年降雨量的增加而增强;当年日照时数大于1 000 h时,生物炭对土壤N_2O的减排效果随年日照时数的增加而减弱。当土壤p H≥6.5时,生物炭对土壤N_2O的减排效果随土壤p H的增加呈先增后减趋势;在壤土中施加生物炭对N_2O的减排效果显著(P0.05),而砂土和黏土不显著(P0.05)。生物炭对覆膜土壤N_2O的减排效果优于不覆膜土壤;生物炭对土壤N_2O的减排效果随施氮肥量增加而减弱,而随生物炭比表面积的增加而增强。当生物炭C/N处于30~500时,生物炭施用下土壤N_2O排放量显著降低(P0.05);当生物炭施加量处于20~160 t×hm-2时,生物炭对土壤N_2O的减排效果随施加量增加而增强。生物炭对土壤N_2O减排的影响存在显著的区域性特征,对华南、华东、华中和东北地区影响显著(P0.05),而对西北地区不显著(P0.05);施氮肥量、生物炭施加量、年均温和年降雨量是影响生物炭减排效果的最主要因素,这些因素的相互作用共同影响生物炭对土壤N_2O的减排效果。该研究可为生物炭在我国农区的推广应用和农田N_2O减排提供参考。     

Impact of biochar addition to soil on greenhouse gas emissions following pig manure application

The application of biochar produced from wood and crop residues, such as sawdust, straw, sugar bagasse and rice hulls, to highly weathered soils under tropical conditions has been shown to influence soil greenhouse gas (GHG) emissions. However, there is a lack of data concerning GHG emissions from soils amended with biochar derived from manure, and from soils outside tropical and subtropical regions. The objective of this study was to quantify the effect on emissions of carbon dioxide (CO₂), nitrous oxide (N₂O) and methane (CH₄) following the addition, at a rate of 18 t ha⁻¹, of two different types of biochar to an Irish tillage soil. A soil column experiment was designed to compare three treatments (n = 8): (1) non-amended soil (2) soil mixed with biochar derived from the separated solid fraction of anaerobically digested pig manure and (3) soil mixed with biochar derived from Sitka Spruce (Picea sitchensis). The soil columns were incubated at 10 °C and 75% relative humidity, and leached with 80 mL distilled water, twice per week. Following 10 weeks of incubation, pig manure, equivalent to 170 kg nitrogen ha⁻¹ and 36 kg phosphorus ha⁻¹, was applied to half of the columns in each treatment (n = 4). Gaseous emissions were analysed for 28 days following manure application. Biochar addition to the soil increased N₂O emissions in the pig manure-amended column, most likely as a result of increased denitrification caused by higher water filled pore space and organic carbon (C) contents. Biochar addition to soil also increased CO₂ emissions. This was caused by increased rates of C mineralisation in these columns, either due to mineralisation of the labile C added with the biochar, or through increased mineralisation of the soil organic matter.     

生物质炭添加对不同pH紫色土硝化作用及N2O排放的影响

生物质炭施用可能对土壤中氮素硝化过程和N₂O排放产生影响。本研究通过室内培养试验,研究铵态氮肥与玉米秸秆生物质炭施用量(0、1%、2%、5%、10%,m/m)对酸性(pH 5.10)和石灰性(pH 8.15)紫色土氮素硝化率、净硝化速率及N₂O排放特征的影响。结果表明:①酸性和石灰性紫色土生物质炭处理平均净硝化速率相比对照分别降低了33.7%～93.7%和7.5%～40.9%,生物质炭添加抑制了酸性和石灰性紫色土硝化作用,在酸性紫色土中生物质炭对硝化作用的抑制作用随施用量的增加而增强,在石灰性紫色土中无明显规律。②与对照相比,酸性紫色土N₂O累计排放量在1%生物质炭和2%生物质炭处理下降幅分别为15.9%和27.7%,在5%和10%生物质炭处理下增幅分别为60.1%和93.2%;石灰性紫色土生物质炭各处理N₂O累积排放量均显著高于对照。③综合考虑,在酸性紫色土中1%、2%生物质炭施用对硝化作用抑制和N₂O减排综合效果最好,但在石灰性紫色土中无明显抑制和减排效果。     

Short-term effects of raw rice straw and its derived biochar on greenhouse gas emission in five typical soils in China

Abstract

A short-term study was conducted to investigate the greenhouse gas emissions in five typical soils under two crop residue management practices: raw rice straw (Oryza sativa L., cv) and its derived biochar application. Rice straw and its derived biochar (two biochars, produced at 350 and 500°C and referred to as BC350 and BC500, respectively) were incubated with the soils at a 5% (weight/weight) rate and under 70% water holding capacity for 28 d. Incorporation of BC500 into soils reduced carbon dioxide (CO₂) and nitrous oxide (N₂O) emission in all five soils by 4?40% and 62?98%, respectively, compared to the untreated soils, whereas methane (CH₄) emission was elevated by up to about 2 times. Contrary to the biochars, direct return of the straw to soil reduced CH₄ emission by 22?69%, whereas CO₂ increased by 4 to 34 times. For N₂O emission, return of rice straw to soil reduced it by over 80% in two soils, while it increased by up to 14 times in other three soils. When all three greenhouse gases were normalized on the CO₂ basis, the global warming potential in all treatments followed the order of straw > BC350 > control > BC500 in all five soils. The results indicated that turning rice straw into biochar followed by its incorporation into soil was an effective measure for reducing soil greenhouse gas emission, and the effectiveness increased with increasing biochar production temperature, whereas direct return of straw to soil enhanced soil greenhouse gas emissions.     

N2O emission mitigation and microbial activity after Biochar and Cao application in a flooded nitrate-rich vegetable soil

Adding easily decomposable organic materials into flooded nitrate-rich soils can effectively decrease the soil nitrate concentration and repair nitrate-rich soil. However, nitrate reduction is usually accompanied with an increase in N₂O emission. This study was conducted to reduce N₂O emission in a nitrate-rich vegetable soil flooded for remediation and amended with biochar. Nitrate-rich vegetable soil was placed in five treatment groups: flooding (F); flooding with rice straw (F?+?RS); flooding with rice straw and 1% biochar (F?+?RS?+?1% biochar); flooding with rice straw and 3% biochar (F?+?RS?+?3% biochar); flooding with rice straw and CaO (F?+?RS?+?CaO). Biochar and CaO reduced the N₂O emission levels relative to the F?+?RS group, with the former being more effective than the latter, achieving reduction of 40.70% (3% biochar) and 17.35% (CaO) of cumulative N₂O emission. The 3% biochar was more effective than the 1% biochar. Regression analysis showed a positive correlation between the abundance of NO reductase gene (norB) and soil N₂O emission flux. In general, biochar and CaO could effectively reduce N₂O emissions from a nitrate-rich vegetable soil during flooding remediation, duo to elevating soil pH and altering denitrifying activity. The norB gene was the most important denitrifying gene driving soil N₂O emission in the remediation.     

Influence of water depth and soil amelioration on greenhouse gas emissions from peat soil columns

Recently, large areas of tropical peatland have been converted into agricultural fields. To be used for agricultural activities, peat soils need to be drained, limed and fertilized due to excess water, low nutrient content and high acidity. Water depth and amelioration have significant effects on greenhouse gas (GHG) production. Twenty-seven soil samples were collected from Jabiren, Central Kalimantan, Indonesia, in 2014 to examine the effect of water depth and amelioration on GHG emissions. Soil columns were formed in the peatland using polyvinyl chloride (PVC) pipe with a diameter of 21 cm and a length of 100 cm. The PVC pipe was inserted vertically into the soil to a depth of 100 cm and carefully pulled up with the soil inside after sealing the bottom. The treatments consisting of three static water depths (15, 35 and 55 cm from the soil surface) and three ameliorants (without ameliorant/control, biochar+compost and steel slag+compost) were arranged using a randomized block design with two factors and three replications. Fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from the soil columns were measured weekly. There was a linear relationship between water depth and CO₂ emissions. No significant difference was observed in the CH₄ emissions in response to water depth and amelioration. The ameliorations influenced the CO₂ and N₂O emissions from the peat soil. The application of biochar+compost enhanced the CO₂ and N₂O emissions but reduced the CH₄ emission. Moreover, the application of steel slag+compost increased the emissions of all three gases. The highest CO₂ and N₂O emissions occurred in response to the biochar+compost treatment followed by the steel slag-compost treatment and without ameliorant. Soil pH, redox potential (Eh) and temperature influenced the CO₂, CH₄ and N₂O fluxes. Experiments for monitoring water depth and amelioration should be developed using peat soil as well as peat soil–crop systems.     

Effects of biochar application on greenhouse gas emissions,carbon sequestration and crop growth in coastal saline soil

To evaluate the benefits of application of biochar to coastal saline soil for climate change mitigation, the effects on soil organic carbon (SOC), greenhouse gases (GHGs) and crop yields were investigated. Biochar was applied at 16 t ha^?1 to study its effects on crop growth (Experiment I). The effects of biochar (0, 3.2, 16 and 32 t ha^?1) and corn stalk (7.8 t ha^?1) on SOC and GHGs were studied using ¹³C stable isotope technology and a static chamber method, respectively (Experiment II). Biochar increased grain mass per plant of the wheat by 27.7% and increased SOC without influencing non‐biochar SOC. On average, 92.3% of the biochar carbon and 16.8% of corn‐stalk carbon were sequestered into the soil within 1 year. The cumulative emissions of CO₂, CH₄ and N₂O were not affected significantly by biochar but cornstalk application increased N₂O emissions by 17.5%. The global warming mitigation potential of the biochar treatments (?3.84 to ?3.17 t CO₂‐eq. ha^?1 t^?1 C) was greater than that of the corn stalk treatment (?0.11 t CO₂‐eq ha^?1 t^?1 C). These results suggest that biochar application improves saline soil productivity and soil carbon sequestration without increasing GHG emissions.     

Effects of biochar amendment on greenhouse gas emissions,net ecosystem carbon budget and properties of an acidic soil under intensive vegetable production

Biochar addition to soils has been frequently proposed as a means to increase soil fertility and carbon (C) sequestration. However, the effect of biochar addition on greenhouse gas emissions from intensively managed soils under vegetable production at the field scale is poorly understood. The effects of wheat straw biochar amendment with mineral fertilizer or an enhanced‐efficiency fertilizer (mixture of urea and nitrapyrin) on N₂O efflux and the net ecosystem C budget were investigated for an acidic soil in southeast China over a 1‐yr period. Biochar addition did not affect the annual N₂O emissions (26–28 kg N/ha), but reduced seasonal N₂O emissions during the cold period. Biochar increased soil organic C and CO₂ efflux on average by 61 and 19%, respectively. Biochar addition greatly increased C gain in the acidic soil (average 11.1 Mg C/ha) compared with treatments without biochar addition (average ?2.2 Mg C/ha). Biochar amendment did not increase yield‐scaled N₂O emissions after application of mineral fertilizer, but it decreased yield‐scaled N₂O by 15% after nitrapyrin addition. Our results suggest that biochar amendment of acidic soil under intensive vegetable cultivation contributes to soil C sequestration, but has only small effects on both plant growth and greenhouse gas emissions.     

Nitrogen fertilization and liming increased CO2 and N2O emissions from tropical ferralsols,but not from a vertisol

The application of nitrogen (N) fertilizers and liming (CaCO₃) to improve soil quality and crop productivity are regarded as effective and important agricultural practices. However, they may increase greenhouse gas (GHG) emissions. There is limited information on the GHG emissions of tropical soils, specifically when liming is combined with N fertilization. We therefore conducted a full factorial laboratory incubation experiment to investigate how N fertilizer (0 kg N ha⁻¹, 12.5 kg N ha⁻¹ and 50 kg N ha⁻¹) and liming (target pH = 6.5) affect GHG emissions and soil N availability. We focussed on three common acidic soils (two ferralsols and one vertisol) from Lake Victoria (Kenya). After 8 weeks, the most significant increase in cumulative carbon dioxide (CO₂) and nitrous oxide (N₂O) fluxes compared with the unfertilized control was found for the two ferralsols in the N + lime treatment, with five to six times higher CO₂ fluxes than the control. The δ¹³C signature of soil-emitted CO₂ revealed that for the ferralsols, liming (i.e. the addition of CaCO₃) was the dominant source of CO₂, followed by urea (N fertilization), whereas no significant effect of liming or of N fertilization on CO₂ flux was found for the vertisol. In addition, the N₂O fluxes were most significantly increased by the high N + lime treatment in the two ferralsols, with four times and 13 times greater N₂O flux than that of the control. No treatment effects on N₂O fluxes were observed for the vertisol. Liming in combination with N fertilization significantly increased the final nitrate content by 14.5%–39% compared with N fertilization alone in all treatment combinations and soils. We conclude that consideration should be given to the GHG budgets of agricultural ferralsols since liming is associated with high liming-induced CO₂ and N₂O emissions. Therefore, nature-based and sustainable sources should be explored as an alternative to liming in order to manage the pH and the associated fertility of acidic tropical soils.     

Combined effects of nitrogen deposition and biochar application on emissions of N2O,CO2 and NH3 from agricultural and forest soils

Abstract

Both nitrogen (N) deposition and biochar can affect the emissions of nitrous oxide (N₂O), carbon dioxide (CO₂) and ammonia (NH₃) from different soils. Here, we have established a simulated wet N deposition experiment to investigate the effects of N deposition and biochar addition on N₂O and CO₂ emissions and NH₃ volatilization from agricultural and forest soils. Repacked soil columns were subjected to six N deposition events over a 1-year period. N was applied at rates of 0 (N0), 60 (N60), and 120 (N120) kg Nh a^?1 yr^?1 without or with biochar (0 and 30 t ha^?1 yr^?1). For agricultural soil, adding N increased cumulative N₂O emissions by 29.8% and 99.1% (p < 0.05) from the N60 and N120 treatments, respectively as compared to without N treatments, and N120 emitted 53.4% more (p < 0.05) N₂O than the N60 treatment; NH₃ volatilization increased by 33.6% and 91.9% (p < 0.05) from the N60 and N120 treatments, respectively, as compared to without N treatments, and N120 emitted 43.6% more (p < 0.05) NH₃ than N60; cumulative CO₂ emissions were not influenced by N addition. For forest soil, adding N significantly increased cumulative N₂O emissions by 141.2% (p < 0.05) and 323.0% (p < 0.05) from N60 and N120 treatments, respectively, as compared to without N treatments, and N120 emitted 75.4% more (p < 0.05) N₂O than N60; NH₃ volatilization increased by 39.0% (p < 0.05) and 56.1% (p < 0.05) from the N60 and N120 treatments, respectively, as compared to without N treatments, and there was no obvious difference between N120 and N60 treatments; cumulative CO₂ emissions were not influenced by N addition. Biochar amendment significantly (p < 0.05) decreased cumulative N₂O emissions by 20.2% and 25.5% from agricultural and forest soils, respectively, and increased CO₂ emissions slightly by 7.2% and NH₃ volatilization obviously by 21.0% in the agricultural soil, while significantly decreasing CO₂ emissions by 31.5% and NH₃ volatilization by 22.5% in the forest soil. These results suggest that N deposition would strengthen N₂O and NH₃ emissions and have no effect on CO₂ emissions in both soils, and treatments receiving the higher N rate at N120 emitted obviously more N₂O and NH₃ than the lower rate at N60. Under the simulated N deposition circumstances, biochar incorporation suppressed N₂O emissions in both soils, and produced contrasting effects on CO₂ and NH₃ emissions, being enhanced in the agricultural soil while suppressed in the forest soil.     

Effects of biochar,earthworms, and litter addition on soil microbial activity and abundance in a temperate agricultural soil

Biochar application to arable soils could be effective for soil C sequestration and mitigation of greenhouse gas (GHG) emissions. Soil microorganisms and fauna are the major contributors to GHG emissions from soil, but their interactions with biochar are poorly understood. We investigated the effects of biochar and its interaction with earthworms on soil microbial activity, abundance, and community composition in an incubation experiment with an arable soil with and without N-rich litter addition. After 37 days of incubation, biochar significantly reduced CO₂ (up to 43 %) and N₂O (up to 42 %), as well as NH₄ ⁺-N and NO₃ ^?-N concentrations, compared to the control soils. Concurrently, in the treatments with litter, biochar increased microbial biomass and the soil microbial community composition shifted to higher fungal-to-bacterial ratios. Without litter, all microbial groups were positively affected by biochar × earthworm interactions suggesting better living conditions for soil microorganisms in biochar-containing cast aggregates after the earthworm gut passage. However, assimilation of biochar-C by earthworms was negligible, indicating no direct benefit for the earthworms from biochar uptake. Biochar strongly reduced the metabolic quotient qCO₂ and suppressed the degradation of native SOC, resulting in large negative priming effects (up to 68 %). We conclude that the biochar amendment altered microbial activity, abundance, and community composition, inducing a more efficient microbial community with reduced emissions of CO₂ and N₂O. Earthworms affected soil microorganisms only in the presence of biochar, highlighting the need for further research on the interactions of biochar with soil fauna.     

Effects of digestate from anaerobically digested cattle slurry and plant materials on soil microbial community and emission of CO2 and N2O

Anaerobic digestion of animal manure and crop residues may be employed to produce biogas as a climate-neutral source of energy and to recycle plant nutrients as fertilizers. However, especially organic farmers are concerned that fertilizing with the digestates may impact the soil microbiota and fertility because they contain more mineral nitrogen (N) and less organic carbon (C) than the non-digested input materials (e.g. raw animal slurry or fresh plant residues). Hence, an incubation study was performed where (1) water, (2) raw cattle slurry, (3) anaerobically digested cattle slurry/maize, (4) anaerobically digested cattle slurry/grass-clover, or (5) fresh grass-clover was applied to soil at arable realistic rates. Experimental unites were sequentially sampled destructively after 1, 3 and 9 days of incubation and the soil assayed for content of mineral N, available organic C, emission of CO₂ and N₂O, microbial phospholipid fatty acids (biomass and community composition) and catabolic response profiling (functional diversity). Fertilizing with the anaerobically digested materials increased the soil concentration of NO₃⁻ ca. 30–40% compared to when raw cattle slurry was applied. Grass-clover contributed with four times more readily degradable organic C than the other materials, causing an increased microbial biomass which depleted the soil for mineral N and probably also O₂. Consequently, grass-clover also caused a ∼10 times increase in emissions of CO₂ and N₂O greenhouse gasses compared to any of the other treatments during the 9 days. Regarding microbial community composition, grass-clover induced the largest changes in microbial diversity measures compared to the controls, where raw cattle slurry and the two anaerobically digested materials (cattle slurry/maize, cattle slurry/grass-clover) only induced minor and transient changes.     

Effect of biochar and nitrapyrin on nitrous oxide and nitric oxide emissions from a sandy loam soil cropped to maize

A field experiment was conducted to evaluate the combined or individual effects of biochar and nitrapyrin (a nitrification inhibitor) on N₂O and NO emissions from a sandy loam soil cropped to maize. The study included nine treatments: addition of urea alone or combined with nitrapyrin to soils that had been amended with biochar at 0, 3, 6, and 12 t ha^?1 in the preceding year, and a control without the addition of N fertilizer. Peaks in N₂O and NO flux occurred simultaneously following fertilizer application and intense rainfall events, and the peak of NO flux was much higher than that of N₂O following application of basal fertilizer. Mean emission ratios of NO/N₂O ranged from 1.11 to 1.72, suggesting that N₂O was primarily derived from nitrification. Cumulative N₂O and NO emissions were 1.00 kg N₂O-N ha^?1 and 1.39 kg NO-N ha^?1 in the N treatment, respectively, decreasing to 0.81–0.85 kg N₂O-N ha^?1 and 1.31–1.35 kg NO-N ha^?1 in the biochar amended soils, respectively, while there was no significant difference among the treatments. NO emissions were significantly lower in the nitrapyrin treatments than in the N fertilization-alone treatments (P?<?0.05), but there was no effect on N₂O emissions. Neither biochar nor nitrapyrin amendment affected maize yield or N uptake. Overall, our results showed that biochar amendment in the preceding year had little effect on N₂O and NO emissions in the following year, while the nitrapyrin decreased NO, but not N₂O emissions, probably due to suppression of denitrification caused by the low soil moisture content.     

Contrasting effects of wheat straw and its biochar on greenhouse gas emissions and enzyme activities in a Chernozemic soil

Biochar produced from plant biomass through pyrolysis has been shown to be much more resistant to biodegradation in the soil as compared with the raw biomass, such as cereal straw that is routinely shredded and discharged on to farm fields in large amounts. Biochar application to soil has also been reported to decrease greenhouse gas (GHG) emissions, although the mechanisms are not fully understood. In this study, the emissions of three main GHGs (CO₂, CH₄, and N₂O) and enzyme activities (urease, β-glycosidase, and dehydrogenase) were measured during a 100-day laboratory incubation of a Chernozemic soil amended with either straw or its biochar at rates of 0.67 and 1.68 % (based on the amount of C added) for the low and high rates, respectively. The biochar application dramatically reduced N₂O emissions, but CO₂ or CH₄ emissions were not different, as compared with the un-amended soil. At the same C equivalent application rate, CO₂ and N₂O emission rates were greater while CH₄ emission rates were lower in straw than in biochar application treatments. The activities of both the dehydrogenase and β-glycosidase significantly declined while that of urease significantly increased with the biochar as compared with the straw treatment. We conclude that pyrolysis of cereal straw prior to land application would significantly reduce CO₂ and N₂O emissions, in association with changed enzyme activities, while increasing the soil C pool through the addition of stable C in the form of biochar.     

Biochar suppresses N2O emissions while maintaining N availability in a sandy loam soil

Nitrous oxide (N₂O) from agricultural soil is a significant source of greenhouse gas emissions. Biochar amendment can contribute to climate change mitigation by suppressing emissions of N₂O from soil, although the mechanisms underlying this effect are poorly understood. We investigated the effect of biochar on soil N₂O emissions and N cycling processes by quantifying soil N immobilisation, denitrification, nitrification and mineralisation rates using ¹⁵N pool dilution techniques and the FLUAZ numerical calculation model. We then examined whether biochar amendment affected N₂O emissions and the availability and transformations of N in soils.Our results show that biochar suppressed cumulative soil N₂O production by 91% in near-saturated, fertilised soils. Cumulative denitrification was reduced by 37%, which accounted for 85–95 % of soil N₂O emissions. We also found that physical/chemical and biological ammonium (NH₄⁺) immobilisation increased with biochar amendment but that nitrate (NO₃⁻) immobilisation decreased. We concluded that this immobilisation was insignificant compared to total soil inorganic N content. In contrast, soil N mineralisation significantly increased by 269% and nitrification by 34% in biochar-amended soil.These findings demonstrate that biochar amendment did not limit inorganic N availability to nitrifiers and denitrifiers, therefore limitations in soil NH₄⁺ and NO₃⁻ supply cannot explain the suppression of N₂O emissions. These results support the concept that biochar application to soil could significantly mitigate agricultural N₂O emissions through altering N transformations, and underpin efforts to develop climate-friendly agricultural management techniques.     

Impacts of straw biochar additions on agricultural soil quality and greenhouse gas fluxes in karst area,Southwest China

Understanding and improving environmental quality by reducing soil nutrient leaching losses, sequestering carbon (C), reducing greenhouse gas (GHG) emissions, and enhancing crop productivity in highly weathered or degraded soils have always been the goals of agroecosystem researchers and producers. Biochar production and soil incorporation strategies have been recently proposed to help attain these goals. However, the effect of such approaches on soil GHG fluxes is highly uncertain and needs to be further assessed before biochar can be used on a large scale. In addition, the duration of these GHG reductions is not known and is of pivotal importance for the inclusion of biochar in climate abatement strategies. In a field trial cultivated with Chinese cabbage (Brassica campestris ssp. pekinensis) and radish (Daucus carota L. var. Sativa Hoffm), rapeseed (Brassica campestris L.) and maize (Zea mays L.) straw-derived biochar was added to the soil at rates of 0, 26, 64 and 128 t ha^?1, in the whole growing season (October 2011–March 2012) to monitor the effect of treatments on soil GHG production/consumption and soil quality 16 months after biochar addition. The results showed that biochar amendment increased soil pH, nitrate nitrogen content, available phosphorus content and soil water content, but decreased soil bulk density. In biochar-treated plots, soil carbon dioxide (CO₂) fluxes were from 20.1 to 87.0% higher than in the control. Soil methane (CH₄) uptakes were increased significantly, by 33.2 and 80.1%, between the biochar amendment at the rate of 64 and 128 t ha^?1 and the control. Soil nitrous oxide (N₂O) fluxes showed no significant difference between biochar amendment and the control. Overall only the CH₄ uptake-promoting effect continued into the long term, 16 months after biochar incorporation. This study demonstrates that the beneficial effects of biochar addition might first come through soil quality improvement and carbon sequestration, rather than through effects on the repression of soil C mineralization or the nitrogen cycle.