Effects of biochar amendment on soil quality, crop yield and greenhouse gas emission in a Chinese rice paddy: A field study of 2 consecutive rice growing cycles

Abstract: Biochar production and application from crop straw had been proposed as one effective countermeasure to mitigate climate change. We conducted a 2-year consecutive field experiment in 2009 and 2010 in rice paddy to gain insight into the consistency over years of biochar effects on rice production and greenhouse gases emissions. Biochar was amended in 2009 before rice transplanting at rates of 0, 10, 20 and 40tha−1, soil emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were monitored with closed chamber method at 7 days interval throughout the whole rice growing season (WRGS) both in 2009 and 2010. The results showed that biochar amendment increased rice productivity, soil pH, soil organic carbon, total nitrogen but decreased soil bulk density in both cycles of rice growth. Soil respiration observed no significant difference between biochar amendment and the corresponding control both in the first and second cycle, respectively. However, biochar amendment decreased nitrous oxide emission but increased methane emission in both cycles. No significant difference in carbon intensity of rice production (GHGI) and global warming potential (GWP) were observed between the biochar amendment at the rate of 10tha−1 and 40tha−1 and control though the GWP and GHGI was increased by 39% and 26% at the rate of 20tha−1 respectively, in the first cycle. However, in the second cycle, both of overall GWP and GHGI were observed significantly decreased under biochar amendment as compared to control, ranging from 7.1% to 18.7% and from 12.4% to 34.8%, respectively. The biochar effect intensity on global warming potential were observed from −2.5% to 39.2% in the first cycle, and from −18.7% to −7.1% in the second cycle. However, the biochar effect intensity on C intensity of rice production was observed from −10.2% to 25.8% in the first cycle, and from −36.9% to −18.6% in the second cycle. Therefore, biochar effect on reducing the overall C intensity of rice production could become stronger in the subsequent cycles than that in the first cycle though a consistently strong effect on reducing N2O emission in a single crop cycle after biochar amendment. Nevertheless, these effects were not found in proportional to biochar amendment rates and a high rice yield but lowest C intensity was achieved under biochar amendment at 10tha−1 in both cycles of the rice paddy in the present study. [Copyright &y& Elsevier]