| China government has committed to reduce total carbon dioxide (CO2) emission per unit of GDP by40%-45%by2020over a baseline in2005. Agro-ecosystems play an important role in the land-atmosphere flux of greenhouse gases. Enhancement of soil C stock was supposed in the Kyoto Protocol to be a ratified and important strategy in carbon sequestration and mitigation, which offers a win-win effect on sustaining crop production and mitigating climatic change. There have been increasing studies on application of biochar from crop residues to croplands as one of the effective countermeasures for enhancing soil C stock and reducing greenhouse gases emission as well as improving crop production in agriculture for the last5years. However, the effects of biochar in the extent and sustainability of such a multiple effect may vary with crop type, soil property and climate conditions as well as feedstocks of crop straw biochar.In order to elucidate the potential of and explore the feasible approaches of biochar application in China’s croplands, two field experiments were respectively initiated with rice paddies in2009from Jiangsu and dry croplands in2010from Henan provinces of China. The field experiments were conducted to study the effect of wheat straw biochar amendment with and without nitrogen fertilizer on crop yield, soil and ecosystem greenhouse gases (CO2, CH4and N2O) emissions from Cd/Pb contaminated and a non-contaminated rice paddy in Tai Lake plain and dry cropland without heavy metal pollution in the Central Great plain of Yellow-Huaihe River. The changes in carbon intensity and the intra-annual variability were assessed in order to address the rational approach for using biochar to enhance soil C stock and to mitigate greenhouse gas emission from croplands. The main results are as fellows:1, Effect of biochar amendment on rice yield and soil methane (CH4) and nitrous oxide (N2O) emissions from a rice paddy in Tai Lake plain (1) Biochar amendment significantly improved soil properties and nutrients content. Biochar amendment at40t ha-1caused an increase in soil pH (H2O) without N fertilization, but no significant difference under biochar amendment with N fertilization. Soil organic carbon (SOC) was increased by17%and57%, and by27%and55%under biochar amendment at rate of20t ha-1and40t ha-1without and with N fertilization, respectively. Hot water extract carbon (HWEC) was found increase under biochar treatment, but no change in labile oxidation carbon (LOC). Total N was increased by23%～39%under biochar amendment. Soil bulk density was decreased from1.01g cm"3without biochar amendment to0.89g cm-3under biochar amendment at40t ha-1.(2) Biochar amendment significantly increased rice yield and agronomic N use efficiency (AEn), decreased N2O emission but increased CH4emission. Without and with N fertilization, rice yield was increased by10%～14%and9%～12%following biochar amendment at10t ha-1,20t ha-1and40t ha-1, respectively. The agronomic N fertilizer use efficiency was observed increase (the value of AEn were1.40kg (kg N)-1,3.54kg (kg N)-1,4.08kg (kg N)-1and4.43kg (kg N)-1under biochar amendment at0t ha-1,10t ha-1,20t ha-1and40t ha-1, respectively). Seasonal amount of N2O emission were sharply decreased by40%～58%under biochar amendment with N fertilization, but without N fertilization (p>0.05). The emission factor (EF) was reduced by48%～69%following biochar treatment. On the contrary, seasonal amount of CH4emission were increased by64%～173%and54%～153%under biochar amendment without and with N fertilization, the value of CH4emission was the highest under20t ha-1treatment without and with N fertilization plot.(3) The greenhouse gas intensity (GHGI) was observed no significant increase. An increase in global warming potential(GWP) and GHGI of CH4and N2O over a100-year horizon was observed under biochar amendment at20t ha-1, but there is no significant difference under biochar amendment at10t ha-1and40t ha-1as corresponding to control (p>0.05).2, Effect of biochar amendment on soil quality, rice yield and greenhouse gas emission in2consecutive rice growing cycles(1) A sustainable effect for consecutive two years was observed on improving soil properties and rice yield. Soil pH (H2O) was increased by0.24unit and0.36unit under biochar amendment at20t ha-1and40t ha-1, respectively; SOC was increased by23%and 54%; by9.1%and15%of total N; by60%and51%of HWEC; however, there is no significant change in LOC under biochar amendment at20t ha-1and40t ha-1, respectively (p>0.05). Soil bulk density was reduced by8.5%and6.4%, respectively. Rice yield was found increased by9.2%~28%under biochar amendment at10t ha-1,20t ha-1and40t ha-1, respectively.(2) Biochar amendment decreased greenhouse gas (CO2, CH4and N2O) intensity of the second rice growing cycle as compared to the first year’s. Soil respiration was observed no significant difference between biochar amendment and no biochar treatment (p>0.05). Seasonal amount of N2O emission from soil was reduced by31%,44%and56%under biochar amendment at10t ha-1,20t ha-1and40t ha-1, respectively. The cumulative CH4emission from soil was lower in the second rice growing cycle than that of the fist rice growing cycle while CH4emission was observed increase by54%and38%under biochar amendment at20t ha-1and40t ha-1as compared to the corresponding control, respectively. No significant difference in GWP and GHGI of CO2, CH4and N2O were observed between the biochar treatment and no biochar amendment in the first rice growing cycle though the GWP and GHGI of CO2, CH4and N2O was increased at rate of20t ha-1treatment; However, both of GWP and GHGI of CO2, CH4and N2O were observed significantly decreased under biochar amendment as compared to the corresponding control in the second rice growing cycle. The higher of rice yield and the lower GHGI was observed under biochar amendment at101ha-1.(3) Seasonal amount of CH4emission was observed decrease but increase in N2O emission from direct seeding paddy soil, overall the GWP of CH4and N2O was reduced under direct seeding treatment as compared to transplanting treatment.3, Biochar amendment decreased annual net exchange of CO2between wheat-rice ecosystem and atmosphere (NEE) of the second rice growing cycle(1) Biochar amendment increased net primary production (NPP) of rice and wheat. The maxium yield and crop biomass of rice and wheat was observed under biochar amendment at rate of10t ha"1. Rice yield and biomass was increased by27.6%and28.7%, by29.1%and24.9%of wheat yield and biomass under biochar amendment at10t ha-1as compared to the corresponding control, respectively.(2) Annual amount of CO2emission from soil, CH4and N2O emissions from ecosystem. Annual amount of CO2emission from soil and CH4emission from rice/wheat ecosystem were observed no significant difference under biochar amendment as compared to no biochar treatment. But annual amount of N2O emission from rice/wheat ecosystem was decreased by39%and41%under biochar amendment at20t ha-1and40t ha-1as compared to control, respectively; but no significant difference was observed under10t ha-1treatment (p>0.05).(3) Golbal warming potential of rice/wheat ecosystem. Biochar amendment decreased annual net exchange of CO2between rice-wheat ecosystem and atmosphere. NEE was decreased by54%,24%and45%; by68%,38%and67%of GWP; by31%,22%and34%of GHGI under biochar amendment at10t ha-1,20t ha-1and40t ha-1as compared to the corresponding control, respectively.4, The effect of biochar amendment on greenhouse gas emissions from soil and ecosystem of Cd/Pb contaminated rice paddy(1) Biochar amendment improved soil properties and decreased Cd/Pb availability. Biochar amendment increased soil pH (H2O) and soil organic carbon; but decreased soil bulk density; DTPA Cd concentration was decreased by25.3%,21.3%and48.7%; by11.9%,17.3%and23.6%of DTPA Pb concentration was observed under biochar amendment at10t ha-1,20t ha-1and40t ha-1as compared to the corresponding control, respectively. CaCl2Cd concentration was decreased by43.5%and40.0%under biochar amendment at20t ha-1and40t ha-1as compared to control, respectively. But no significant difference was observed in CaCl2Pb concentration (p>0.05).(2) Biochar amendment decreased soil respiration but increased carbon sink of Cd/Pb contaminated rice ecosystem. Seasonal amount of N2O emission from soil and ecosystem were reduced by34%～48%and11%～50%, respectively; but increased by30%～49%of seasonal amount of CH4emission from soil under biochar amendment at10t ha-1,20t ha-1and40t ha-1as compared to corresponding control. Seasonal amount of CH4emission from ecosystem was observed increased by31%under biochar amendment at40t ha-1. Seasonal amount of CO2emission from soil was decreased by16%and24%under biochar amendment at20t ha-1and40t ha-1as compared to control, respectively. But seasonal amount of CO2emission from ecosystem was observed increased. Ecosystem carbon sink of Cd and Pb contaminated paddy was observed increased under biochar treatment. The GWP of ecosystem was decreased by54%and63%under biochar amendment at20t ha-1and40t ha-1as compared to control, respectively. No significant difference was observed under biochar amendment at10t ha-1.5, Effect of biochar amendment on maize yield and greenhouse gas emissions from a low fertility dry cropland(1) Biochar amendment improved soil properties and increased maize yield. Biochar amendment increased SOC and total N but decreased soil bulk density and had no effect on soil pH(H2O) and mineral N (NH4+and NO3-) in treatments both with and without N fertilization. Without N fertilization, SOC was found to increase by57.8%and44.0%; by42.2%and25.0%with N fertilization under biochar amendment at40t ha’1and20t ha-1as compared to control, respectively. Without N fertilization, total soil N content was enhanced by31.0%under biochar amendment at40t ha-1and by24.1%at20t ha-1as compared to no biochar treatment, respectively, while there was no significant difference between the biochar treatments with N fertilization. Maize yield was increased by15.8%and7.3%without N fertilization, and by12.1%and8.8%with N fertilization under biochar amendment at20t ha-1and40t ha-1, respectively. The estimated AEn value was increased from1.25kg (kg N)-1under no biochar treatment to2.28kg (kg N)-1under biochar amendment at40t ha-1.(2) Biochar amendment decreased N2O emission, and decreased the global warming potential and greenhouse gas intensity of CH4and N2O. There was no effect on soil CO2emission under biochar amendment (p=0.19); N fertilization reduced soil CO2emission (p<0.0001). Total N2O emission was decreased by10.7%and by41.8%under biochar amendment at20t ha-1and40t ha" as compared to no biochar amendment with N fertilization. The EF was observed decreased. But increased seasonal amount of CH4emission. Overall, total GWP and GHGI of CH4and N2O was observed decreased by9.8%and41.5%, by23.8%and47.6%under biochar amendment at20t ha-1and40t ha-1with N fertilization, respectively, while no change in without N fertilization (p>0.05).6, An approach for measurement the carbon sequestration and mitigation of straw biochar amendmentThe comparative effect of straw burned (baseline) and biochar amendment (program) on greenhouse gas emission and carbon sink in relation to agricultural application was evaluated on the basis of the manufacturing process of Sanli New Energy Company, Henan, China. The stoichimetric coefficient of non-CO2emission was based on the results from the authors study and from publications. The effect of soil type and farmland management (paddy soil and dry crop) on non-CO2emission, and the consecutive effect of biochar amendment on CH4and N2O emission were integratedly taken into account. Using this method, the overall carbon sink is from249kg CO2-Ce t-1to398kg CO2-Ce t-1per ton of straw, indicating that straw biochar has a substantial effect on carbon sequestration and mitigation. |
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