The Impact Of Different Straw Returning Forms And Rice Varieties On CH₄ And N₂O Emission In A Double Rice Field

The rice paddy ecosystem is one of the most important source of methane and nitrous oxide emission. It is significant for low carbon agriculture development to study the impact of different form of straw and different amendment of biochar into rice paddy on greenhouse gas emission and the rice yields, to study the GHGs emission reduction of different biochar amendmen based on the LCA method. Rice varieties have a significant impact on methane emissions, selecting the rice varieties which have less emissions and higher yields plays an important role in ensuring food security and slowing global warming.The research of different straw retuning forms and different amendment of biochar has been studied during 2014-2015 in the typical double rice field in south China. The research include six treatments:(1)traditional operation without biochar(CK);(2)biochar amendment at 5t·hm-2(BC1);(3)biochar amendment at 10t·hm-2(BC2);(4)biochar amendment at 20t·hm-2(BC3);(5)raw rice straw residue return(RS);(6)composted rice straw residue return(RI). Static chamber-GC(gas chromatography)method was used to monitor greenhouse gas emission of different treatments. Then, the method of LCA was applied to calculate greenhouse gas emission in each stage, including the collection of raw materials, biochar production, transportation, dissemination, carbon sequestration, rice growth season. In addition, the net income and the carbon intensity of unit net income was caculated. Finally, the feasibility in GHGs emission reduction and in the economy of different amendment of biochar was evaluated. The research of rice variety include nine common varieties in Guangdong province. Static chamber-GC(gas chromatography)method was also used to monitor greenhouse gas emission of different varieties, then combined with rice yields to select the rice variety which has less emission and higher yields. The conclusions show as follow:(1)Put the form of straw into biochar returning to field can effectively inhibit rice paddy greenhouse gas emissions. In 2014 and 2015, the average emission reduction percentage of different amendment of biochar were 25.3% and 23.1% compared with CK, respectively. Between the different biochar amendment, the high biochar amendment can effectively inhibit rice paddy greenhouse gas emissions, the average emission reduction percentage in 2014 and 2015 of BC1,BC2,BC3 were 15.1%, 25.3% and 32.3% compared with CK, respectively.(2) By the method of LCA which was used to calculate the carbon footprint of different biochar amendment, the result showed that the footprint of BC1、BC2 and BC3 are lower than CK, and that BC3 shows a better effect on carbon sequestration and carbon content. 2012a-2015 a, the cumulative amount of carbon sequestration has reached 16.4tCO2·hm-2 which is feasible in reducing of greenhouse gas emissions. The net income of different biochar amendment are still lower than CK during 2012a-2015 a, among which the treatment of BC3 is minimum and thus is not feasible in economy, while the net income gap between BC1 and CK is minimum. Therefore, the effect of biochar short-term application(4a) under the LCA evaluation method shows that the optimal recommended biochar amendment is 5t·hm-2(BC1).(3) The raw rice straw residue return and composted rice straw residue return increased the rice paddy greenhouse gas emissions. In 2014-2015, the average emission percentage of the two ways of straw returning forms were 217.3%, 107.1% compared with CK, respectively. The average emission percentage in 2014 and 2015 of the raw rice straw residue return and composted rice straw residue return were 208.1%, 116.3% compared with CK, respectively. The CO2 equivalent emissions of the treatment of returning straw to field directly was significantly higher than that of straw added inoculants returning.(4) The research of different rice varieties has showed that HFZ and YXZ-6 have less GHGs emission and higher yields and their carbon intensity of unit rice yield is lower than other rice varieties. The average carbon intensity of the two rice varieties in 2014 and 2015 were 0.23 kg·kg-1 and 0.24 kg·kg-1 respectively.