Effects of Biochar Addition on CO2 and N2O Emissions following Fertilizer Application to a Cultivated Grassland Soil

Carbon (C) sequestration potential of biochar should be considered together with emission of greenhouse gases when applied to soils. In this study, we investigated CO₂ and N₂O emissions following the application of rice husk biochars to cultivated grassland soils and related gas emissions tos oil C and nitrogen (N) dynamics. Treatments included biochar addition (CHAR, NO CHAR) and amendment (COMPOST, UREA, NO FERT). The biochar application rate was 0.3% by weight. The temporal pattern of CO₂ emissions differed according to biochar addition and amendments. CO₂ emissions from the COMPOST soils were significantly higher than those from the UREA and NO FERT soils and less CO₂ emission was observed when biochar and compost were applied together during the summer. Overall N₂O emission was significantly influenced by the interaction between biochar and amendments. In UREA soil, biochar addition increased N₂O emission by 49% compared to the control, while in the COMPOST and NO FERT soils, biochar did not have an effect on N₂O emission. Two possible mechanisms were proposed to explain the higher N₂O emissions upon biochar addition to UREA soil than other soils. Labile C in the biochar may have stimulated microbial N mineralization in the C-limited soil used in our study, resulting in an increase in N₂O emission. Biochar may also have provided the soil with the ability to retain mineral N, leading to increased N₂O emission. The overall results imply that biochar addition can increase C sequestration when applied together with compost, and might stimulate N₂O emission when applied to soil amended with urea.     

Impact of six lignocellulosic biochars on C and N dynamics of two contrasting soils

Both soil and biochar properties are known to influence greenhouse gas emissions from biochar‐amended soils, but poor understanding of underlying mechanisms challenges prediction and modeling. Here, we examine the effect of six lignocellulosic biochars produced from the pyrolysis of corn stover and wood feedstocks on CO₂ and N₂O emissions from soils collected from two bioenergy cropping systems. Effects of biochar on total accumulated CO₂‐C emissions were minimal (<0.45 mg C g^?1 soil; <10% of biochar C), consistent with mineralization and hydrolysis of small labile organic and inorganic C fractions in the studied biochars. Comparisons of soil CO₂ emissions with emissions from microbially inoculated quartz–biochar mixtures (‘quartz controls’) provide evidence of soil and biochar‐specific negative priming. Five of six biochar amendments suppressed N₂O emissions from at least one soil, and the magnitude of N₂O emissions suppression varied with respect to both biochar and soil types. Biochar amendments consistently decreased final soil NO₃^? concentrations, while contrasting effects on pH, NH₄⁺, and DOC highlighted the potential for formation of anaerobic microsites in biochar‐amended soils and consequential shifts in the soil redox environment. Thus, results implicated both reduced substrate availability and redox shifts as potential factors contributing to N₂O emission suppression. More research is needed to confirm these mechanisms, but overall our results suggest that soil biochar amendments commonly reduce N₂O emissions and have little effect on CO₂ emissions beyond the mineralization and/or hydrolysis of labile biochar C fractions. Considering the large C credit for the biochar C, we conclude that biochar amendments can reduce greenhouse gas emissions and enhance the climate change mitigation potential of bioenergy cropping systems.     

Dynamic responses of nitrous oxide emission and nitrogen use efficiency to nitrogen and biochar amendment in an intensified vegetable field in southeastern China

Intensive vegetable production exhibits contrasting characteristics of high nitrous oxide (N₂O) emissions and low nitrogen use efficiency (NUE). In an effort to mitigate N₂O emissions and improve NUE, a field experiment with nine consecutive vegetable crops was designed to study the combined effects of nitrogen (N) and biochar amendment and their interaction on soil properties, N₂O emission and NUE in an intensified vegetable field in southeastern China. We found that N application significantly increased N₂O emissions, N₂O–N emission factors and yield‐scaled N₂O emissions by 51–159%, 9–125% and 14–131%, respectively. Moreover, high N input significantly decreased N partial factor productivity (PFPN) and even yield during the seventh to ninth vegetable crops along with obvious soil degradation and mineral N accumulation. To the contrary, biochar amendment resulted in significant decreases in cumulative N₂O emissions, N₂O–N emission factor and yield‐scaled N₂O emissions by 5–39%, 16–67% and 14–53%, respectively. In addition, biochar significantly increased yield, PFPN and apparent recovery of N (ARN). Although without obvious influence during the first to fourth vegetable crops, biochar amendment mitigated N₂O emissions during the fifth to ninth vegetable crops. The relative effects of biochar amendments were reduced with increasing N application rate. Hence, while high N input produced adverse consequences such as mineral N accumulation and soil degradation in the vegetable field, biochar amendment can be a beneficial agricultural strategy to mitigate N₂O emissions and improve NUE and soil quality in vegetable field.     

Effect of biochar amendment on maize yield and greenhouse gas emissions from a soil organic carbon poor calcareous loamy soil from Central China Plain

Aims

A field experiment was conducted to investigate the effect of biochar on maize yield and greenhouse gases (GHGs) in a calcareous loamy soil poor in organic carbon from Henan, central great plain, China.

Methods

Biochar was applied at rates of 0, 20 and 40?t?ha^?1 with or without N fertilization. With N fertilization, urea was applied at 300?kg?N ha^?1, of which 60% was applied as basal fertilizer and 40% as supplementary fertilizer during crop growth. Soil emissions of CO₂, CH₄ and N₂O were monitored using closed chambers at 7?days intervals throughout the whole maize growing season (WMGS).

Results

Biochar amendments significantly increased maize production but decreased GHGs. Maize yield was increased by 15.8% and 7.3% without N fertilization, and by 8.8% and 12.1% with N fertilization under biochar amendment at 20?t?ha^?1 and 40?t?ha^?1, respectively. Total N₂O emission was decreased by 10.7% and by 41.8% under biochar amendment at 20?t?ha^?1 and 40?t?ha^?1 compared to no biochar amendment with N fertilization. The high rate of biochar (40?t?ha^?1) increased the total CO₂ emission by 12% without N fertilization. Overall, biochar amendments of 20?t?ha^?1 and 40?t?ha^?1 decreased the total global warming potential (GWP) of CH₄ and N₂O by 9.8% and by 41.5% without N fertilization, and by 23.8% and 47.6% with N fertilization, respectively. Biochar amendments also decreased soil bulk density and increased soil total N contents but had no effect on soil mineral N.

Conclusions

These results suggest that application of biochar to calcareous and infertile dry croplands poor in soil organic carbon will enhance crop productivity and reduce GHGs emissions.     

Impact of biochar application on nitrogen nutrition of rice, greenhouse-gas emissions and soil organic carbon dynamics in two paddy soils of China

Aims

Two field microcosm experiments and ¹⁵N labeling techniques were used to investigate the effects of biochar addition on rice N nutrition and GHG emissions in an Inceptisol and an Ultisol.

Methods

Biochar N bioavailability and effect of biochar on fertilizer nitrogen-use efficiency (NUE) were studied by ¹⁵N-enriched wheat biochar (7.8803 atom% ¹⁵N) and fertilizer urea (5.0026 atom% ¹⁵N) (Experiment I). Corn biochar and corn stalks were applied at 12 Mg?ha^?1 to study their effects on GHG emissions (Experiment II).

Results

Biochar had no significant impact on rice production and less than 2 % of the biochar N was available to plants in the first season. Biochar addition increased soil C and N contents and decreased urea NUE. Seasonal cumulative CH₄ emissions with biochar were similar to the controls, but significantly lower than the local practice of straw amendment. N₂O emissions with biochar were similar to the control in the acidic Ultisol, but significantly higher in the slightly alkaline Inceptisol. Carbon-balance calculations found no major losses of biochar-C.

Conclusion

Low bio-availability of biochar N did not make a significantly impact on rice production or N nutrition during the first year. Replacement of straw amendments with biochar could decrease CH₄ emissions and increase SOC stocks.     

Can biochar reduce soil greenhouse gas emissions from a Miscanthus bioenergy crop?

Energy production from bioenergy crops may significantly reduce greenhouse gas (GHG) emissions through substitution of fossil fuels. Biochar amendment to soil may further decrease the net climate forcing of bioenergy crop production, however, this has not yet been assessed under field conditions. Significant suppression of soil nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions following biochar amendment has been demonstrated in short‐term laboratory incubations by a number of authors, yet evidence from long‐term field trials has been contradictory. This study investigated whether biochar amendment could suppress soil GHG emissions under field and controlled conditions in a Miscanthus × Giganteus crop and whether suppression would be sustained during the first 2 years following amendment. In the field, biochar amendment suppressed soil CO₂ emissions by 33% and annual net soil CO₂ equivalent (eq.) emissions (CO₂, N₂O and methane, CH₄) by 37% over 2 years. In the laboratory, under controlled temperature and equalised gravimetric water content, biochar amendment suppressed soil CO₂ emissions by 53% and net soil CO₂ eq. emissions by 55%. Soil N₂O emissions were not significantly suppressed with biochar amendment, although they were generally low. Soil CH₄ fluxes were below minimum detectable limits in both experiments. These findings demonstrate that biochar amendment has the potential to suppress net soil CO₂ eq. emissions in bioenergy crop systems for up to 2 years after addition, primarily through reduced CO₂ emissions. Suppression of soil CO₂ emissions may be due to a combined effect of reduced enzymatic activity, the increased carbon‐use efficiency from the co‐location of soil microbes, soil organic matter and nutrients and the precipitation of CO₂ onto the biochar surface. We conclude that hardwood biochar has the potential to improve the GHG balance of bioenergy crops through reductions in net soil CO₂ eq. emissions.     

Effect of biochar amendment on the soil-atmosphere exchange of greenhouse gases from an intensive subtropical pasture in northern New South Wales, Australia

We assessed the effect of biochar incorporation into the soil on the soil-atmosphere exchange of the greenhouse gases (GHG) from an intensive subtropical pasture. For this, we measured N₂O, CH₄ and CO₂ emissions with high temporal resolution from April to June 2009 in an existing factorial experiment where cattle feedlot biochar had been applied at 10 t ha^?1 in November 2006. Over the whole measurement period, significant emissions of N₂O and CO₂ were observed, whereas a net uptake of CH₄ was measured. N₂O emissions were found to be highly episodic with one major emission pulse (up to 502 ??g N₂O-N m^?2 h^?1) following heavy rainfall. There was no significant difference in the net flux of GHGs from the biochar amended vs. the control plots. Our results demonstrate that intensively managed subtropical pastures on ferrosols in northern New South Wales of Australia can be a significant source of GHG. Our hypothesis that the application of biochar would lead to a reduction in emissions of GHG from soils was not supported in this field assessment. Additional studies with longer observation periods are needed to clarify the long term effect of biochar amendment on soil microbial processes and the emission of GHGs under field conditions.     

Variation in Soil Methane Release or Uptake Responses to Biochar Amendment: A Separate Meta-analysis

Agricultural soils play an important role in the atmospheric methane (CH₄) budget, where paddy soils can contribute significant CH₄ to atmosphere whereas upland soils may act as a source or sink of atmospheric CH₄, dependent on soil water conditions. Biochar amendments have effects on soil CH₄ production or oxidation processes in individual experiments, but the causative mechanisms are yet to be fully elucidated. To synthesize the response of soil CH₄ release or uptake to biochar amendment, we performed a meta-analysis using data from 61 peer-reviewed papers with 222 updated paired measurements. When averaged across all studies, biochar amendment significantly decreased CH₄ release rates by 12% for paddy soils and 72% for upland soils, and CH₄ uptake rates by 84% for upland soils. Neither soil CH₄ release nor uptake responses to biochar amendment were significant in field soils. Nitrogen (N) fertilizer application would weaken the response of soil CH₄ release or uptake to biochar amendment. Biochar-incurred decreases in soil CH₄ release and uptake rates were the largest in medium-textured soils or neutral-pH soils. Soil CH₄ release or uptake responses to biochar were also significantly altered by biochar characteristics, such as feedstock source, C/N ratio, pH, and pyrolysis temperature. The results of this synthesis suggest that the role of biochar in soil CH₄ mitigation potential might have been exaggerated, particularly in fields when biochar is applied in combination with N fertilizer.     

Successive straw biochar application as a strategy to sequester carbon and improve fertility: A pot experiment with two rice/wheat rotations in paddy soil

Aims

A pot study spanning four consecutive crop seasons was conducted to compare the effects of successive rice straw biochar/rice straw amendments on C sequestration and soil fertility in rice/wheat rotated paddy soil.

Methods

We adopted 4.5 t ha^?1, 9.0 t ha^?1 biochar and 3.75 t ha^?1 straw for each crop season with an identical dose of NPK fertilizers.

Results

We found no major losses of biochar-C over the 2-year experimental period. Obvious reductions in CH₄ emission were observed from rice seasons under the biochar application, despite the fact that the biochar brought more C into the soil than the straw. N₂O emissions with biochar were similar to the controls without additives over the 2-year experimental period. Biochar application had positive effects on crop growth, along with positive effects on nutrient (N, P, K, Ca and Mg) uptake by crop plants and the availability of soil P, K, Ca and Mg. High levels of biochar application over the course of the crop rotation suppressed NH₃ volatilization in the rice season, but stimulated it in the wheat season.

Conclusions

Converting straw to biochar followed by successive application to soil is viable for soil C sequestration, CH₄ mitigation, improvements of soil and crop productivity. Biochar soil amendment influences NH₃ volatilization differently in the flooded rice and upland wheat seasons, respectively.     

Influence of Willow Biochar Amendment on Soil Nitrogen Availability and Greenhouse Gas Production in Two Fertilized Temperate Prairie Soils

The potential of biochar to improve numerous soil physical, chemical and biological properties is well known. However, previous research has concentrated on old and highly weathered tropical soils with poor fertility, while reports regarding the influence of biochar application on relatively young and fertile temperate prairie soils are limited. Furthermore, the mechanism(s) underlying biochar-induced effects on the plant availability of inorganic nitrogen (N) fertilizers and their relationship to greenhouse gas production is not well understood. The objective of this study was to determine the effect of a biochar soil amendment, produced by slow pyrolysis using shrub willow (Salix spp.) bioenergy feedstock, on CO₂, N₂O and CH₄ fluxes by two contrasting marginal soils from Saskatchewan, Canada with and without added urea, over a 6-week incubation period. Biochar decreased soil N availability after 6 weeks only in the lower organic matter (Brown) soil, with no effect on the Black soil, regardless of fertilizer N addition, which was attributed to soil N immobilization by heterotrophs mineralizing the labile biochar-carbon. There appeared to be a synergistic effect when combining biochar and urea, evidenced by enhanced urease activity and higher initial nitrification rates compared to biochar or fertilization alone. The accelerated urea hydrolysis in the presence of biochar may increase NH₃ volatilization losses associated with urea fertilization and, therefore, warrants further investigation. The decreased N₂O emissions following biochar addition, with (both soils) or without (Black soil) fertilizer N, could be due to decreased ammonium and nitrate availability, along with changes in denitrification potential as related to improved aeration. Biochar significantly reduced the water-filled pore space, which concurrently increased CH₄ consumption in both soils. The lack of biochar effect on CO₂ emissions from either soil, with or without fertilizer N, suggests enhanced CO₂ consumption by autotrophic nitrifiers. Biochar application appears to be an effective management approach for improving N₂O and CH₄ fluxes in temperate prairie soils.     

Soil greenhouse gas emissions from inorganic fertilizers and recycled oil palm waste products from Indonesian oil palm plantations

A continuous rise in the global demand for palm oil has resulted in the large‐scale expansion of oil palm plantations and generated environmental controversy. Efforts to increase the sustainability of oil palm cultivation include the recycling of oil mill and pruning residues in the field, but this may increase soil methane (CH₄) emissions. This study reports the results of yearlong field‐based measurements of soil nitrous oxide (N₂O) and CH₄ emissions from commercial plantations in North Sumatra, Indonesia. One experiment investigated the effects of soil‐water saturation on N₂O and CH₄ emissions from inorganic fertilizers and organic amendments by simulating 25 mm rainfall per day for 21 days. Three additional experiments focused on emissions from (a) inorganic fertilizer (urea), (b) combination of enriched mulch with urea and (c) organic amendments (empty fruit bunches, enriched mulch and pruned oil palm fronds) applied in different doses and spatial layouts (placed in inter‐row zones, piles, patches or bands) for a full year. The higher dose of urea led to a significantly higher N₂O emissions with the emission factors ranging from 2.4% to 2.7% in the long‐term experiment, which is considerably higher than the IPCC standard of 1%. Organic amendments were a significant source of both N₂O and CH₄ emissions, but N₂O emissions from organic amendments were 66%–86% lower than those from inorganic fertilizers. Organic amendments applied in piles emitted 63% and 71% more N₂O and CH₄, respectively, than when spread out. With twice the dose of organic amendments, cumulative emissions were up to three times greater. The (simulated) rainwater experiment showed that the increase in precipitation led to a significant increase in N₂O emissions significantly, suggesting that the time of fertilization is a critical management option for reducing emissions. The results from this study could therefore help guide residue and nutrient management practices to reduce emissions while ensuring better nutrient recycling for sustainable oil palm production systems.     

炉渣与生物炭施加对稻田土壤产甲烷菌群落结构的影响

为了了解废弃物施加处理影响稻田甲烷排放通量的微生物学机制,对稻田分别进行炉渣、生物炭单一施加和混合施加处理,分析施加处理条件下早、晚稻拔节期稻田土壤的理化性质,并采用PCR-RFLP技术及克隆测序对稻田土壤中的产甲烷菌群落组成多样性及其结构进行分析。研究结果表明:早稻拔节期,混施处理显著提高土壤盐度和pH;晚稻拔节期,混施处理显著提高土壤盐度,炉渣和混施处理显著提高pH。香农-威纳指数(H')和辛普森指数(D)显示:炉渣、生物炭和混施处理提高了稻田土壤产甲烷菌的多样性。群落组成分析结果表明:稻田土壤产甲烷菌主要含有甲烷微菌目(Methanomicrobiales)、甲烷杆菌目(Methanobacteriales)、甲烷八叠球菌目(Methanosarcinales)、甲烷球菌目(Methanococcales)、甲烷胞菌目(Methanocellales)和Methanomassiliicoccales等6大类群,其中甲烷微菌目(Methanomicrobiales)为优势类群。从属水平的群落结构来看,与对照相比,3种施加处理均降低了早稻土壤Methanomassiliicoccus相对丰度;生物炭处理还降低了Methanosarcina相对丰度。初步认为Methanomassiliicoccus和Methanosarcina这2个菌属与CH_4排放量减少密切相关。     

Experimental evidence for sequestering C with biochar by avoidance of CO2 emissions from original feedstock and protection of native soil organic matter

There is a need for further studies to compare the decomposition of biochar to that of the original feedstock and determine how these amendments affect the cycling of native organic matter (NOM) of different soils to improve our understanding of the resulting net C sequestration potential. A 510‐days incubation experiment was conducted (i) to investigate the evolution of CO₂ from soils amended with either fresh corn stover (CS) or with biochars produced from fresh CS at either 350 (CS‐350) or 550 °C (CS‐550), and (ii) to evaluate the priming effect of these amendments on NOM decomposition. Two soil types were studied: an Alfisol and an Andisol, with organic C contents of 4% and 10%, respectively. Except for the controls (with no C addition), all treatments received 7.18 t C ha^?1. We measured C efflux in short‐term intervals and its isotopic signature to distinguish between C evolved from C₄ amendments and C₃‐dominated NOM. Emission rates were then integrated for the whole time period to cover total emissions. Total CO₂‐C evolved from the original C in fresh CS, CS‐350 and CS‐550 was greater in the Andisol (78%, 13% and 14%) than in the Alfisol (66%, 8% and 7%). For both soils, (i) no significant differences (P > 0.05) were observed in the rate of CO₂ evolution between controls and biochar treatments; and (ii) total accumulated CO₂ evolved from the uncharred amendment was significantly higher (P < 0.05) than that from the other treatments. In the Alfisol, a significant (P < 0.05) net positive priming effect on NOM decomposition was observed when amended with fresh CS, while the opposite was detected in biochar treatments. In the Andisol, no significant (P > 0.05) net priming effect was observed. A C balance indicated that the C lost from both biochar production and decomposition ‘broke even’ with that lost from fresh residue decomposition after <35 weeks. The ‘break‐even’ point was reached earlier in the Andisol, in which the fresh CS mineralizes faster. These results provided experimental evidence for the potential of biochar to sequester C and avoid CO₂ emissions from original feedstock while protecting native soil organic matter.     

Carbon footprint of rice production under biochar amendment – a case study in a Chinese rice cropping system

As a controversial strategy to mitigate global warming, biochar application into soil highlights the need for life cycle assessment before large‐scale practice. This study focused on the effect of biochar on carbon footprint of rice production. A field experiment was performed with three treatments: no residue amendment (Control), 6 t ha^?1 yr^?1 corn straw (CS) amendment, and 2.4 t ha^?1 yr^?1 corn straw‐derived biochar amendment (CBC). Carbon footprint was calculated by considering carbon source processes (pyrolysis energy cost, fertilizer and pesticide input, farmwork, and soil greenhouse gas emissions) and carbon sink processes (soil carbon increment and energy offset from pyrolytic gas). On average over three consecutive rice‐growing cycles from year 2011 to 2013, the CS treatment had a much higher carbon intensity of rice (0.68 kg CO₂‐C equivalent (CO₂‐C_e) kg^?1 grain) than that of Control (0.24 kg CO₂‐C_e kg^?1 grain), resulting from large soil CH₄ emissions. Biochar amendment significantly increased soil carbon pool and showed no significant effect on soil total N₂O and CH₄ emissions relative to Control; however, due to a variation in net electric energy input of biochar production based on different pyrolysis settings, carbon intensity of rice under CBC treatment ranged from 0.04 to 0.44 kg CO₂‐C_e kg^?1 grain. The results indicated that biochar strategy had the potential to significantly reduce the carbon footprint of crop production, but the energy‐efficient pyrolysis technique does matter.     

Biochar co-compost improves nitrogen retention and reduces carbon emissions in a winter wheat cropping system

Organic amendments, such as compost and biochar, mitigate the environmental burdens associated with wasting organic resources and close nutrient loops by capturing, transforming, and resupplying nutrients to soils. While compost or biochar application to soil can enhance an agroecosystem's capacity to store carbon and produce food, there have been few field studies investigating the agroecological impacts of amending soil with biochar co-compost, produced through the composting of nitrogen-rich organic material, such as manure, with carbon-rich biochar. Here, we examine the impact of biochar co-compost on soil properties and processes by conducting a field study in which we compare the environmental and agronomic impacts associated with the amendment of either dairy manure co-composted with biochar, dairy manure compost, or biochar to soils in a winter wheat cropping system. Organic amendments were applied at equivalent C rates (8 Mg C ha⁻¹). We found that all three treatments significantly increased soil water holding capacity and total plant biomass relative to the no-amendment control. Soils amended with biochar or biochar co-compost resulted in significantly less greenhouse gas emissions than the compost or control soils. Biochar co-compost also resulted in a significant reduction in nutrient leaching relative to the application of biochar alone or compost alone. Our results suggest that biochar co-composting could optimize organic resource recycling for climate change mitigation and agricultural productivity while minimizing nutrient losses from agroecosystems.     

Mitigation of ammonia,nitrous oxide and methane emissions from manure management chains: a meta‐analysis and integrated assessment

Livestock manure contributes considerably to global emissions of ammonia (NH₃) and greenhouse gases (GHG), especially methane (CH₄) and nitrous oxide (N₂O). Various measures have been developed to mitigate these emissions, but most of these focus on one specific gas and/or emission source. Here, we present a meta‐analysis and integrated assessment of the effects of mitigation measures on NH₃, CH₄ and (direct and indirect) N₂O emissions from the whole manure management chain. We analysed the effects of mitigation technologies on NH₃, CH₄ and N₂O emissions from individual sources statistically using results of 126 published studies. Whole‐chain effects on NH₃ and GHG emissions were assessed through scenario analysis. Significant NH₃ reduction efficiencies were observed for (i) housing via lowering the dietary crude protein (CP) content (24–65%, compared to the reference situation), for (ii) external slurry storages via acidification (83%) and covers of straw (78%) or artificial films (98%), for (iii) solid manure storages via compaction and covering (61%, compared to composting), and for (iv) manure application through band spreading (55%, compared to surface application), incorporation (70%) and injection (80%). Acidification decreased CH₄ emissions from stored slurry by 87%. Significant increases in N₂O emissions were found for straw‐covered slurry storages (by two orders of magnitude) and manure injection (by 26–199%). These side‐effects of straw covers and slurry injection on N₂O emission were relatively small when considering the total GHG emissions from the manure chain. Lowering the CP content of feed and acidifying slurry are strategies that consistently reduce NH₃ and GHG emissions in the whole chain. Other strategies may reduce emissions of a specific gas or emissions source, by which there is a risk of unwanted trade‐offs in the manure management chain. Proper farm‐scale combinations of mitigation measures are important to minimize impacts of livestock production on global emissions of NH₃ and GHG.     

Soil greenhouse gas,carbon content,and tree growth response to biochar amendment in western United States forests

Restoring overstocked forests by thinning and pyrolyzing residual biomass produces biochar and other value‐added products. Forest soils amended with biochar have potential to sequester carbon (C), improve soil quality, and alter greenhouse gas (GHG) emissions without depleting nutrient stocks. Yet, few studies have examined the effects of biochar on GHG emissions and tree growth in temperate forest soils. We measured GHG emissions, soil C content, and tree growth at managed forest sites in Idaho, Montana, and Oregon. We applied biochar amendments of 0, 2.5, or 25 Mg/ha to the forest soil surface. Flux of carbon dioxide and methane varied by season; however, neither were affected by biochar amendment. Flux of nitrous oxide was not detected at these nitrogen‐limited and unfertilized forest sites. Biochar amendment increased soil C content by 41% but did not affect tree growth. Overall, biochar had no detrimental effects on forest trees or soils. We conclude that biochar can be used harmlessly for climate change mitigation in forests by sequestering C in the soil.     

Annual net greenhouse gas balance in a halophyte (Helianthus tuberosus) bioenergy cropping system under various soil practices in Southeast China

A full accounting of net greenhouse gas balance (NGHGB) and greenhouse gas intensity (GHGI) was examined in an annual coastal reclaimed saline Jerusalem artichoke-fallow cropping system under various soil practices including soil tillage, soil ameliorant, and crop residue amendments. Seasonal fluxes of soil carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) were measured using static chamber method, and the net ecosystem exchange of CO₂ (NEE) was determined by the difference between soil heterotrophic respiration (R_H) and net primary production (NPP). Relative to no-tillage, rotary tillage significantly decreased the NPP of Jerusalem artichoke while it had no significant effects on the annual R_H. Rotary tillage increased CH₄ emissions, while seasonal or annual soil N₂O emissions did not statistically differ between the two tillage treatments. Compared with the control plots, soil ameliorant or straw amendment enhanced R_H, soil CH_4, and N₂O emissions under the both tillage regimes. Annual NGHGB was negative for all the field treatments, as a consequence of net ecosystem CO₂ sequestration exceeding the CO₂-equivalents released as CH₄ and N₂O emissions, which indicates that Jerusalem artichoke-fallow cropping system served as a net sink of GHGs. The annual net NGHGB and GHGI were estimated to be 11–21% and 4–8% lower in the NT than in RT cropping systems, respectively. Soil ameliorant and straw amendments greatly increased NPP and thus significantly decreased the negative annual net NGHGB. Overall, higher NPP but lower climatic impacts of coastal saline bioenergy production would be simultaneously achieved by Jerusalem artichoke cultivation under no-tillage with improved saline soil conditions in southeast China.     

Chloropicrin Emission Reduction by Soil Amendment with Biochar

Biochar has sorption capacity, and can be used to enhance the sequestration of volatile organic contaminants such as pesticides in soil. Chloropicrin (CP) is an important soil fumigant for the production of many fruit and vegetable crops, but its emissions must be minimized to reduce exposure risks and air pollution. The objective of this study was to determine the capacity of biochar to adsorb CP and the effect of biochar amendments to soil on CP emission, concentration in the soil gas phase, degradation in soil and CP bioactivity for controlling soil borne pests. CP emission and concentration in the soil air phase were measured from packed soil columns after fumigant injection at 20-cm depth and application of selected doses of biocharto the surface 5 cm soil. Laboratory incubation and fumigation experiments were conducted to determine the capacity of biochar to adsorb CP, the effects on CP degradation and, separately, CP’s bioactivity on soil borne pests in soil amended with biochar. Biochar amendment at 2% to 5% (w/w) greatly reduced total CP emission losses by 85.7% - 97.7% compared to fumigation without biochar. CP concentrations in the soil gas-phase, especially in the top 5 cm of soil, were reduced within 48 h following application. The half-life of CP decreased from 13.6 h to 6.4 h as the biochar rate increased from 0% to 5%. CP and its metabolite (dichloronitromethane) both degraded more rapidly in pure biochar than in soil. The biochar used in the present study had a maximum adsorption capacity for CP of less than 5 mg g^-1. There were no negative effects on pathogen and nematode control when the biochar used in this study was less than 1% (on a weight basis) in soil. Biochar amendment to soil reduced the emissions of CP. CP concentrations in the top 5 cm of soil gas-phase were reduced. CP degradation was accelerated with the addition of biochar. The biochar used in the present study had a low adsorption capacity for CP. There were no negative effects on pathogen and nematode control when the biochar amendment rate was less than 1% (by weight). The findings would be useful for establishing guidelines for biochar use in soil fumigation.