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Abstract Biochar application is proposed having a potential of inhibiting greenhouse gases emissions from paddy fields, which is considered to be a main source of atmospheric greenhouse gases. However, the impacts of biochar on greenhouse gases from paddy field have not been investigated under controlled irrigation (CI). Field experiments were conducted during 2016–2017 to determine the effect of biochar application combined with controlled irrigation on rice yield and methane (CH 4) and nitrous oxide (N 2 O) emission from paddy fields in the Taihu Lake Region of China. Four treatments (0 t ha−1 biochar +CI, 20 t ha−1 biochar +CI, 40 t ha−1 biochar +CI, and 40 t ha−1 biochar + flooding irrigation (FI), named CA, CB, CC and FC, respectively) were designed in this study. The results showed that the effect of biochar application on greenhouse gases emissions from paddy fields under controlled irrigation had significant interannual differences. In the first season, CC decreased the global warming potential(GWP) of CH 4 and N 2 O emission, and the CB increased the GWP of CH 4 and N 2 O emission compared to CA, but these differences were not significant. For the second season, CB and CC decreased the GWP of CH 4 and N 2 O emission by 35.7% and 21.5% significantly compared to CA due to the significant mitigation of CH 4 and N 2 O emission. Biochar application significantly increased CH 4 emission and decreased N 2 O emission from paddy fields under flooding irrigation compared to controlled irrigation (CC), which led to the FC's GWP was 1.70 and 5.47 times higher than CC's in the first and second season. In addition, biochar application increased soil organic carbon, dissolved organic carbon and total nitrogen contents of paddy fields under controlled irrigation. And CB and CC increased rice yield by 16.7% and 24.3% and irrigation water productivity by 26.1% and 30.8% compared with CA (mean of two seasons). These results suggest that 20 and 40 t ha−1 biochar can be utilized under controlled irrigation not only for mitigation of CH 4 and N 2 O emission but also to increase rice yield, soil fertility and irrigation water productivity. Therefore, the combination of biochar amendment and controlled irrigation might be a good option for mitigating greenhouse gases emission and realizing the sustainable utilization of soil and water resources of paddy fields in the Taihu Lake Region of China. Highlights • 20 t ha−1 biochar application significantly increased soil DOC, TN, NH 4 +-N and decreased NO 3 −-N concentrations. • Biochar amendments increased rice yield and irrigation water productivity (mean of two rice seasons). • Biochar application combined with controlled irrigation reduced the mean GWP of two rice seasons. [ABSTRACT FROM AUTHOR]

This study investigates the effect of feedstock drying on the emissions of polycyclic aromatic hydrocarbons (PAHs) associated with the particulate matter (PM) produced during the co-generation of biochar and bioenergy. Raw pyrolysis volatile mixtures were generated from the pyrolysis of rice husk at 400, 500, 600, 700, and 800 °C using a laboratory-scale continuous pyrolysis-combustion system and combusted at 850 °C. PM samples from the combustion were collected and analysed for 15 priority PAH species with a gas chromatography/mass spectrometer (GC/MS). It was found that the utilization of the as received (AR) rice husk resulted in significantly greater energy-based yields of PM 10 (1.2 times at 400 °C and 1.6 times at 800 °C) than the dried rice husk. The majority of the increase was of the PM 2.1-10 size fraction. The PM-bound PAH concentration was found to be 2.1 and 2.8 times higher for the AR rice husk at 400 and 800 °C, respectively. This resulted in a significant increase in the energy-based yield of PAHs over the entire volatile production temperature range for the AR rice husk. Nevertheless, the majority of the PM-bound PAH species generated from the AR rice husk consisted of 2 and 3 ring PAHs (naphthalene, acenapthylene, and acenaphthene) with relatively low toxicity. The concentration of 4, 5, and 6 ring PAHs was generally lower than that generated from the dried rice husk. This resulted in the benzo( a )pyrene-equivalent toxicity of the PM generated from the AR rice husk being lower than the dried counterpart. [ABSTRACT FROM AUTHOR]

To understand the impacts of wood vinegar (WV), a by-product of biochar production, on N 2 O and CH 4 emissions and their total global warming potential (GWP t ) from N-fertilized rice paddy soil, a soil column experiment was conducted using three treatments: 240 kg urea-N ha −1 accompanied with 0, 5, and 10 t WV ha −1 , respectively. Results showed that N 2 O and CH 4 emission flux patterns were dominated by water regime of rice growth cycle, which was independent with WV application. The total N 2 O, CH 4 emission loads and GWP t over rice season of three N received treatments were 6.41–8.85 kg ha −1 , 127.7–405.0 kg ha −1 , and 5.24–12.03 t CO 2 -e ha −1 , respectively. Rice seasonal N 2 O and CH 4 emissions were synchronously mitigated by 22.4% and 36.4%, respectively, when WV was applied at 5 t ha −1 . Consequently, 5 t ha −1 WV treatment reduced 31.5% of GWP t compared with the urea treatment. In addition, 10 t ha −1 WV treatment exerted a more positive effect on suppressing N 2 O with 27.6% reduction. However, it increased GWP t by 57.2% because its CH 4 emission load was increased by 101.8%. In conclusion, WV amendment applied at an appropriate rate (5 t ha −1 ) or combination with other CH 4 control technologies were suggested to reduce both N 2 O and CH 4 emissions and thereby the GWP t in N-fertilized rice paddy soil. [ABSTRACT FROM AUTHOR]

It is increasingly recognized that the addition of biochar to soil has potential to mitigate climate change and increase soil fertility by enhancing carbon (C) storage. However, the effect of biochar on yield and nitrous oxide (N 2 O) emissions from upland fields remains unclear. In this study, a one-year field experiment was conducted in an area of calcareous fluvo-aquic soil to assess and quantify the effect of maize straw biochar in reducing N 2 O loss during 2014–2015 in the North China Plain. Eight treatments were designed as follows: no nitrogen (N) fertilizer (control, CK); biochar application at rates of 3 (B3), 6 (B6) and 12 (B12) t ha −1 ; chemical fertilizer (NPK) application at 200 kg N ha −1 (F); and fertilizer plus biochar application at rates of 3 (FB3), 6 (FB6) and 12 (FB12) t ha −1 . Crop yield, N 2 O fluxes, soil mineral N concentrations, and soil auxiliary parameters were measured following the application of treatments during each season. During the maize growing season, N 2 O emission was 0.57 kg N 2 O-N ha −1 under CK treatment, and increased to 0.88, 0.93 and 1.10 kg N 2 O-N ha −1 under B3, B6 and B12, respectively. In contrast, N 2 O emissions were significantly reduced by 31.4–39.9% ( P < 0.05) under FB treatments compared with F, and the N 2 O emission factor of the applied N was reduced from 1.36% under F to 0.71–0.85% under FB. There was also a significant interaction effect of fertilizer and biochar on N 2 O emissions ( P < 0.01). During the wheat growing season, biochar had no effect on N 2 O emissions regardless of the fertilizer regime. Biochar application did not affect maize yield; however, a significant increase in wheat yield of 16.6–25.9% ( P < 0.05) was observed without N fertilization. Nevertheless, a reduction in wheat yield was measured at a biochar rate of 12 t ha −1 with fertilization. Overall, under maize cropping, N 2 O emissions per unit yield of grain, biomass, grain N and biomass N (yield-scaled N 2 O emissions) were significantly reduced by 32.4–39.9% under FB compared with F treatment, regardless of the biochar application rate. Biochar did not affect yield-scaled N 2 O emissions in wheat. Decreased soil bulk density with biochar is suggested to reduce the denitrification potential and N 2 O emissions; while increased retention capacity of fertilizer N in biochar-added soil decreased wheat growth and yield. These findings suggest that N fertilization plus biochar application at 3 t ha −1 is a practical strategy for reducing yield-scaled N 2 O emissions from maize fields in the North China Plain. [ABSTRACT FROM AUTHOR]

Controlling the production and subsequent emissions of greenhouse gases (GHGs) from paddy fields is crucial to minimize the climatic impacts arising from crop production. The application of chemical or biological amendments is one possible way to limit the production of GHGs in paddy soils. Yet, few existing studies have examined the impacts of applying fertilizers originated from industrial and agricultural wastes on soil GHG production and its governing factors in subtropical paddy fields. In this study, we examined the effects of various agricultural and industrial amendments, including biochar, steel slag, shell slag, gypsum slag, and slag-derived silicate and calcium fertilizers, on the production potential of GHGs in an early paddy field in southeast China. The mean CO 2 production rates from soils amended with steel slag as well as silicate and calcium fertilizers were significantly higher than those of the controls by 13.4% and 18.6%, respectively ( P < 0.05). Mean soil CH 4 production rates from the plots amended with steel slag, biochar, shell slag, and gypsum slag were significantly lower than those of the controls by 42.5%, 36.1%, 60.8%, and 61.8%, respectively ( P < 0.05). Meanwhile, we found no significant difference in mean soil N 2 O production rates between the control and any of the treatments ( P > 0.05). Overall, the soil production rate of CO 2 was positively correlated with that of CH 4 ( P < 0.05), but negatively correlated with that of N 2 O ( P < 0.05). When compared to the controls, the ratio of soil CO 2 :CH 4 production increased significantly in the plots receiving biochar, and silicate and calcium fertilizer amendments ( P < 0.05), while that of CO 2 :N 2 O production increased significantly only in the biochar-amended plots. Soil CH 4 :N 2 O production ratio decreased significantly in the plots amended with steel slag and gypsum slag, as compared to the controls ( P < 0.05). Our results suggest that the application of biochar, shell slag and gypsum slag would help reduce greenhouse gas production and mitigate climate change impacts of rice cultivation, largely attributable to the reduction in methanogenesis. [ABSTRACT FROM AUTHOR]

Biochar, i.e. pyrolysed biomass, as a soil conditioner is gaining increasing attention in research and industry, with guidelines and certifications being developed for biochar production, storage and handling, as well as for application to soils. Adding water to biochar aims to reduce its susceptibility to become air-borne during and after the application to soils, thereby preventing, amongst others, human health issues from inhalation. The Bagnold model has previously been modified to explain the threshold friction velocity of coal particles at different moisture contents, by adding an adhesive effect. However, it is unknown if this model also works for biochar particles. We measured the threshold friction velocities of a range of biochar particles (woody feedstock) under a range of moisture contents by using a wind tunnel, and tested the performance of the modified Bagnold model. Results showed that the threshold friction velocity can be significantly increased by keeping the gravimetric moisture content at or above 15% to promote adhesive effects between the small particles. For the specific biochar of this study, the modified Bagnold model accurately estimated threshold friction velocities of biochar particles up to moisture contents of 10%. [ABSTRACT FROM AUTHOR]

Field experiments were conducted to determine the effects of nitrogen (N) fertilization and biochar addition on the net global warming potential (net GWP), greenhouse gas intensity (GHGI) and net ecosystem economic budget (NEEB). These experiments were conducted in an intensive vegetable field with 4 consecutive vegetable crops in 2012 and 2013 in southeastern China. The experiment was conducted with a 3 2 factorial design in triplicate at N fertilizer rates of 0, 1475, 1967 kg N ha −1 and biochar rates of 0, 20, and 40 t ha −1 . Although CH 4 emissions were not obviously affected by N fertilization, N 2 O emissions increased by 27.2–116.2% and the net GWP increased by 30.6–307.2%. Consequently, the GHGI increased significantly, but vegetable yield and the NEEB did not improve. Furthermore, biochar amendments did not significantly influence CH 4 emissions, but significantly decreased the N 2 O emissions by 1.7–25.4%, the net GWP by 89.6–700.5%, and the GHGI by 89.5–644.8%. In addition, vegetable yields significantly increased by 2.1–74.1%, which improved the NEEB. Thus, N fertilization did not increase vegetable yields or the NEEB. However, N fertilization did increase the net GWP and GHGI. In contrast, biochar additions resulted in lower N 2 O emissions and net GWP and GHGI, but increased vegetable yield and the NEEB in the intensive vegetable production system. Therefore, appropriate biochar amendment should be studied to combat changing climate and to improve the economic profits of vegetable production. [ABSTRACT FROM AUTHOR]