Studies On The Effect Of Biochar Application On Paddy Greenhouse Gas Emissions

In order to explore the impact of biochar application on the greenhouse gas (GHG) emissions in paddy field and the influence to the physical-chemical properties of soil and the crop yield, so as to reveal the role of biochar in rice field ecosystems, provide theoretical guidance for agricultural environment protection, and provide new ideas for mitigation of global climate change, three kind of biochar made from rice straw, bamboo charcoal waste and pecan shell were used in this study, typical paddy soil from Ningshao plain, Zhejiang Province was collected to conduct pot and field experiment. Furthermore, we use DNDC (De-Nitrification and De-Composition) model version9.5research the paddy field CO2, CH4, and N2O emissions, by the fitting degree between the simulated values and the measured values of the field to estimate the emission reduction potential of biochar. The main conclusions are as follows:(1)Filed experiments results:①Conventional fertilizer application resulted in paddy greenhouse gases (CH4, N2O and CO2) emission increases, while returing the carbonized biomass to paddy soil can significantly inhibit the greenhouse gas emission. In the field trials we use three kinds of biochar, but their inhibition effect of three kinds of greenhouse gas emissions are different. For CH4, pecan shell charcoal works best,the low application amount(2t.hm-2) has the most significant inhibition effect,55.95%lower than the conventional treatment; as to N2O emission reduction, straw charcoal (2t.hm-2) is the most effective,70.7%lower than the conventional treatment; compare with the soil CH4, N2O emission reduction, the effect of CO2emissions reduction by charcoal application is not obvious, only if applying high-level amount(10t·hm-2) bamboo charcoal, the effect is obvious,41.7%lower than conventional fertilization, straw and bamboo charcoal’s effect is not significant, and different application amount did not present a significant difference.②Fresh straw application is one of the important reasons leading to CH4emissions, but carbon emission can be decreased efficiently by returning carbonized straw biomass. Experimental results showed that, compared with directly applying fresh straw, applying biochar can reduce CH4emissions by18.2%; applying carbonized straw biochar can make accumulated N2O emissions reduced by33.6%. Adding straw did not result in accumulated CO2emissions higher than normal processing without straw. Compared with returning straw directly, returning carbonized rice straw(2t.hm-2) only decrease flooded paddy soil CO2emissions by about9.3%,with no significant difference.③The influence of biochar application on soil properties. During the period of two years field trials, straw charcoal, bamboo-char and pecan shell charcoal application can increase rice paddy soil organic matter content, and it increased with the increase of biochar application amount. Biochar application can also increase the soil’s other nutrient content, and has certain nutrient preserving function. In addition, biochar application can effectively reduce the soil’s bulk density, and with larger application amount, the effect is more significant, and straw-char’s effect is the most obvious.(2)Pot experiment results:①Compared with the blank control, conventional fertilizer application resulted in paddy greenhouse gases (CH4, N2O and CO2) emissions increase by17%,168%,58%respectively, while returing the carbonized bamboo waste biomass to paddy soil can significantly inhibit the CH4and N2O emissions, compared with conventional fertilizer application, it decreased by64.3%-92.9%and72.3%～93.9%respectively, with larger application amount,the effect is more significant; but the meantime, the emissions of CO2only decreased by15.3%-39.4%.②The influence of biochar application on soil properties:the pot experiment get the same conclusion with field experiment. The organic matter content of pot experiment soil is1.4%originally, after planting one season,the organic content of the control group soil increased to1.5%, Compared to the CK treatment, three bamboo-char treatments’organic content increased to1.7%、1.9%and2.2%respectively. At the same time, the soil bulk density decreased with the application of bamboo-char. At the begining of the test, mix up the soil with biochar, the soil bulk density of all the treatments are1.25g.cm-3, after planting one year, the bulk density respectively are1.24g·cm-3(CK)、1.23g·cm-3(TT)、1.16g·cm-3(BC1)、1.12g·cm-3(BC2)、1.11g·cm-3(BC3).Thus it can be seen that bulk density of the CK and conventional treatment is almost of no change, and compared with the CK treatment, the soil bulk density of bamboo charcoal application treatments were significantly decreased, and soil porosity increased, so the soil air permeability improved.(3)Contrast between the DNDC simulation value and field measured values showed that DNDC model can estimate the field rice yield. The greenhouse gas simulation results showed that the DNDC model fit well with the measured values of conventional treatment, but there has no located input parameters specially according to the biochar characteristics, so the simulation results cannot express the effect of biochar amendment. The future research should pay more attention on perfecting the DNDC model of biochar’s impact in rice field ecosystems.