Agricultural soil is the main source of greenhouse gas emissions, among which carbon dioxide (CO2) is an important greenhouse gas, impacting the global climate. In China, as a large rice-producing country, carbon sequestration and CO2 mitigation in paddy soil are crucial for the mitigation of global climate change. While biochar has been widely used in the mitigation of soil greenhouse gas emissions, the application site of biochar, i.e., whether or not it is the same as its feedstocks, may generate different effects on soil CO2 emissions due to the differences in the element and nutrient concentrations in its feedstocks, especially when applied in fertilized soil. In order to explore the effects of biochar application with different feedstocks on the mitigation of CO2 emissions from paddy soil, this experiment took paddy soil in a red soil area as the research object, using rice straw and Camellia oleifera fruit shell as raw materials to produce biochar (adding an amount of 40 g kg−1 soil) and urea as an external nitrogen source (adding an amount of 200 mg kg−1 soil). The effects of two different types of biochar derived from feedstocks with different producing origins on the CO2 emissions from paddy soil were studied via laboratory control incubation studies. The results showed that (1) the effects of rice straw biochar addition on the soil pH, NO3−-N and total available nitrogen (AN) content were significantly higher than those of Camellia oleifera fruit shell biochar (the scale of the increase was higher by 6.40%, 579.7% and 180.1%, respectively). (2) The CO2 emission rate and cumulative emissions of soil supplemented with rice straw biochar were significantly lower than in that supplemented with Camellia oleifera fruit shell biochar (decreases of 28.0% and 27.5%, respectively). Our findings suggest that the efficiency of emission mitigation of rice straw biochar is better than that of Camellia oleifera fruit shell applied to paddy soil. While future studies considering more types of greenhouse gases will be necessary to expand these findings, this study indicates that biochar prepared from in situ feedstock can be used to reduce greenhouse gas emissions in rice fields, so as to ensure sustainable development and achieve energy conservation and emission reduction goals. This study will benefit future agricultural practices when choosing biochar as a greenhouse gas mitigation strategy in the context of global warming, as well as other global changes following global warming, caused by elevated atmospheric greenhouse gases.
