Impact Of Combining Application Of FGDG And Biochar On Carbon Emissions From Paddy Soils

Carbon and non-carbon containing greenhouse gases pose a serious threat to environmental climatic conditions.However,anthropogenic emissions from carboncontaining greenhouse gases i.e.carbon dioxide（CO₂）and methane（CH₄）are of great concern in paddy fields.The total global agriculture emissions from 2001 to 2011 were estimated to have increased from 4.7 billion tonnes of CO₂ equivalent to over 5.3 billion tonnes,indicating a 14% increase.Asia where the staple crop is mainly rice contributed about 44%.As of 2008,the global agricultural GHG emissions were estimated at 10-12% of the total anthropogenic greenhouse gas emissions.China accounts for about 19% of the world’s rice paddy field planting area.Therefore,Carbon emissions from paddy soils must be analyzed towards the implementation of mitigation measures.FGDG is a by-product of coal-fired power plants that is rich in Ca2+and SO42-ions with main chemical composition being Ca SO4.2H2 O.Its mechanism in paddy soils is that Ca2+ ions in the soil environment can react with CO₂ to produce Ca CO3 which is more chemically stable and enhances the fixation of carbon in the soil,consequently reducing CO₂ emissions.Alternatively,SO42-ions can improve the microbial community of sulfate-reducing bacteria,boost competition against hydrogen and acetic acid,which in turn impedes the activity of methanogens.Thereby,indirectly reducing CH₄ emissions and at the same time encouraging CO₂ emission.Biochar is a type of black carbon formed from carbonaceous material created with the intent to be used as a soil ameliorant.It is a stable substrate created from organic material that has been combusted under low or no oxygen conditions through the process of pyrolysis.Biochar has been commended for improving the soil structure,enhancing the soil environmental conditions,decreasing GHG emission and increasing the soil carbon sink.The improvement of soil environmental conditions such as soil moisture,low soil p H,enhances soil microbial communities.This increases metabolism and respiration,eventually resulting in soil CO₂ emissions under aerobic conditions.Other researchers have reported that utilization of biochar as a soil amendment can increase the availability of soil soluble organic carbon.Thus,providing substrate for methanogens,which may promote CH₄ emissions from the soil,under anaerobic conditions,as is the case in paddy soils.The research focused on establishing whether FGDG would counter the CO₂ emission effect promoted by Biochar.Thus,the impact of the combined use of FGDG and biochar on Carbon emission from paddy soils in Chongqing.CO₂ and CH₄ emissions from paddy soils were measured in-situ by static dark box gas chromatography during the rice-growing period and the fallow period.The experiment comprised of six treatment with different combinations of FGDG and biochar application rates,and each treatment was replicated three times.T0（no rice was planted,no FGDG and biochar was applied）,T1（rice was planted,but no FGDG and biochar was applied）,T2（rice was planted,4t hm-2 biochar was applied and no FGDG was applied）,T3（rice was planted,4t hm-2 biochar and 4t hm-2 FGDG was applied）,T4（rice was planted,4t hm-2 biochar and 8t hm-2 FGDG was applied）and T5（rice was planted,4t hm-2 biochar hm-2 and 16 t hm-2 FGDG was applied）.CO₂ and CH₄ emissions were analyzed and the NECB of paddy field ecosystem was assessed to ascertain whether FGDG can prevent the effect of biochar on carbon emissions.The research findings were as follows:1.Variations of soil properties in paddy soils.During the rice-growing period,when the single application of 4t hm-2 biochar was compared with the mixed application of 4t hm-2 biochar and 16 t hm-2 FGDG,FGDG significantly increased the average DOC in the soil by 33.21%（P<0.05）.However,there was no significant change in the DOC content for the other treatments.During the fallow period,the bare treatment（T0）was compared to treatments（T1-T5）in which rice was planted,results indicated that planting rice significantly improved the soil moisture content by 11.36%（P>0.05）.On the other hand,the other treatments showed no significant changes in the moisture content.In both the rice-growing period and fallow period,rice planting,biochar application alone,and the combination of desulfurized gypsum and biochar application had no significant effect on soil temperature,Eh and p H（P > 0.05）.2.Instantaneous variations of CH₄ emission flux from paddy fieldDuring the rice-growing period,the average CH₄ emission fluxes [mg C m-2h-1] from treatments T0,T1,T2,T3,T4 and T5 were 7.60±0.67,4.87±0.98,7.58±0.83,1.60±0.21,1.01±0.28 and 0.51±0.09,respectively.Comparing between the bare treatment（T0）and the treatments（T1-T5）in which rice was planted,planting rice reduced the average CH₄ emission flux by 35.92%,but the change was insignificant（P>0.05）.The single application of biochar in treatment T2 at 4t hm-2 showed that biochar increased the average CH₄ emission flux by 55.65%,but the change was not significant.When the single application of 4t hm-2 biochar（T2）was compared with the treatments in which biochar and FGDG were combined（T3-T5）at different application rates,there was a significant reduction on the average CH₄ emission flux from treatments T3 T4 and T5 by 78.89%,86.68% and 93.27%,respectively（P>0.05）.During the fallow period,the average CH₄ emission fluxes [mg C m-2h-1] from the paddy soils under different treatments were 0.09±0.01,0.20±0.05,0.21±0.07,0.21±0.05,0.19±0.05 and 0.18±0.02,respectively.Comparing the bare treatment T0 with treatments in which rice was planted,results indicated that planting rice increased the average CH₄ emission flux by 122.22%,but the change was insignificant（P>0.05）.The single application of biochar（T2）insignificantly increased the average CH₄ emission flux by 5%,while the combined application of FGDG and biochar（T3-T5）insignificantly decreased the average CH₄ emission flux,at a rate of 0-14.29%.3.Cumulative CH₄ emission from paddy soilsDuring the rice-growing period,the cumulative CH₄ emission fluxes from treatments T0,T1,T2,T3,T4 and T5 were 130.19,86.30,130.82,26.90,16.70 and 7.64 kg C hm-2,respectively.When the bare treatment（T0）was compared with treatments（T1-T5）in which rice was planted,results revealed that rice planting reduced CH₄ cumulative emissions by 33.71%.However,the change was insignificant,indicating that rice planting had no significant impact on CH₄ emissions from paddy soils（P>0.05）.The application of biochar alone in treatment T2 significantly increased the cumulative CH₄ emissions by 51.59%,on the other hand,the combined application of FGDG and biochar in treatments T3,T4 and T5 significantly reduced the cumulative emissions of CH₄ by 79.44%,87.23% and 94.16%,respectively（P>0.05）.The rate of reduction in cumulative CH₄ emissions increased with an increase in the rate of FGDG application,indicating that FGDG can inhibit the negative effects of biochar increased CH₄ emission,and the higher the FGDG application rate,the more noticeable were the inhibition effect.In the fallow period,the cumulative emission fluxes of CH₄ from treatments T0,T1,T2,T3,T4 and T5 were 6.24,9.63,10.90,32.18,7.45 and 8.69 kg C hm-2,respectively.Comparing the bare treatment（T1）to the treatments in which rice was planted（T1-T5）,rice planting showed an insignificant increment in cumulative CH₄ emissions by 54.33%（P>0.05）.The sole application of biochar（T2）also insignificantly increased the cumulative CH₄ emissions by 13.19%.The cumulative emissions of CH₄ increased by 195.23%,31.65% and 20.28% with the mixture of FGDG applied at the rate of 4,8 and 16thm-2 respectively,without any significant changes.During the whole experiment period,CH₄ emissions were mainly concentrated in the rice-growing period,accounting for 45.53%⁹5.4% of the whole research period.4.Instantaneous variations of CO₂ emission flux from paddy fieldDuring the rice-growing period,the average CO₂ emission fluxes [mg C m-2h-1] from paddy soils for treatments T0,T1,T2,T3,T4 and T5 were 51.71±9,60.56±7.91,64.64±8.14,74.08±10.74,68.48±8.96 and 63.07±8.92,respectively.Comparing between the bare treatment（T0）and treatments（T1-T5）in which rice was planted,planting rice increased the average CO₂ emission flux by 17.12%,but the change was insignificant（P>0.05）.The single application of biochar in treatment T2 at 4t hm-2 showed that biochar insignificantly increased the average CO₂ emission flux by 6.74%.The combined application of FGDG and biochar in treatments T3 and T4 where FGDG was applied at the rate of 4t hm-2 and 8t hm-2 increased the average CO₂ emission fluxes by 14.60% and 5.94% respectively,while FGDG applied at 16 t hm-2 decreased CO₂ emission fluxes by 2.43%,but the changes were not significant.During the fallow period,the average CO₂ emission fluxes from paddy soils were 63.97±7.16,58.89±8,61.43±7.56,74.93±8.45,55.24±9.11 and 41.96±6.33 mg C m-2h-1,respectively.Comparing between the bare treatment（T0）and treatments（T1-T5）in which rice was planted,planting rice reduced the average CO₂ emission flux by 7.94%,but the change was insignificant（P>0.05）.The single application of biochar in treatment T2 at 4t hm-2 showed that biochar insignificantly increased the average CO₂ emission flux by 4.31%.When 4t hm-2 FGDG was mixed with biochar,the average CO₂ emission flux increased by 21.98%,while the average CO₂ emission flux decreased by 10.08% and 31.70% when 8 and 16 t hm-2 of FGDG combined with biochar,all changes were not significant.However,it should be noted that CO₂ analyzed in this study was from microbial respiration and soil organic matter decomposition.5.Cumulative CO₂ emission from paddy soilThrough the rice-growing period,the cumulative CO₂ emissions from treatments T0,T1,T2,T3,T4 and T5 treatment were 923.70,1084.41,1028.16,1301.07,1220.63 and 1091.76 kg C hm-2,respectively.Comparing between the bare treatment（T0）and treatments（T1-T5）in which rice was planted,planting rice increased the cumulative CO₂ emissions by 17.40%,but the change was not significant, demonstrating that planting rice had an insignificant effect on CO₂ emissions in the paddy soils（P>0.05）.The cumulative CO₂ emissions were somewhat reduced by 5.19% by the sole application of biochar and slightly increased by the combined application of FGDG and biochar.The cumulative CH₄ emissions from treatments T3,T4 and T5 increased by 26.54%,18.72% and 6.19%,respectively,however,there were no significant changes（P>0.05）.Throughout the fallow period,cumulative CO₂ emission fluxes from each treatment were 2678.3,3215.31,3130.76,4032.53,2783.47 and 2326.62 kg C hm-2,respectively.Comparing between the bare treatment（T0）and treatments（T1-T5）in which rice was planted,planting rice increased the cumulative CO₂ emissions by 20.05%,but the change was not significant（P>0.05）.The single application of biochar in treatment T2 insignificantly reduced the cumulative CO₂ emissions by 2.63%.on the other hand,the cumulative CO₂ emissions were increased by 28.80% under the combined application of 4t hm-2 FGDG,and decreased by 11.09% and 25.69% with the mixed application of 8 and 16 t hm-2 FGDG respectively,and the changes were not significant.Throughout the entire observation period,the cumulative CO₂ emission flux from paddy soils was mainly concentrated in the fallow period,accounting for about 68.06%⁷5.6% of the whole research period.6.Net ecosystem carbon budget of paddy fieldsThroughout the rice-growing period,the single application of biochar and combined application of FGDG and Biochar had no significant effect on the net carbon balance in paddy fields（P>0.05）.In the fallow period,the mixed application of 4t hm-2 FGDG increased the carbon expenditure significantly,while the mixed application of 16 t hm-2 FGDG reduced the carbon expenditure significantly（P < 0.05）.In summary,during the rice-growing period,the single application of biochar increased CH₄ emission and reduced CO₂ emission to a certain degree,but the change was insignificant.Additional application of FGDG significantly reduced CH₄ emission from the paddy soils（P<0.05）,while CO₂ emission slightly increased.During the fallow period,there was no significant effect on CH₄ and CO₂ emissions from solely applying biochar or the combined application with FGDG（P>0.05）.The decrease in CH₄ emission can be attributed to the addition of FGDG which increased SO42-in the paddy soils,boosted sulfate-reducing bacteria,which enhanced the competitive advantage with methanogens,and inhibited the generation and emission of CH₄.In contrast,hydrogen and acetic acid are important substrates for CH₄ production,but they are also consumed by SO42-oxidation,and their concentration can be reduced below the threshold available for methanogens,which may have contributed to the inhibition of CH₄ production.Also,the reduction product S2-from SO42-may be toxic to methanogens.Simultaneously,the application of biochar may intensify the population of methane-oxidizing bacteria and reduce the ratio of methane-producing bacteria to methane-oxidizing bacteria,and may also inhibit the production of CH₄.The effects of the combined application of FGDG and biochar on carbon-containing greenhouse gases requires further attention.