Biochar enhances mitigation of CH4 and N2O emissions from rice fields under different irrigation and tillage managements

The present field study assessed the effects of different managements on greenhouse gas (GHG) emissions in Mediterranean rice crop. Given the pressing need to identify sustainable agricultural practices that mitigate GHG emissions while maintaining productivity, the effects on GHG emisions of two irrigation methods (permanent flooding and sprinkler) and two tillage practices (conventional tillage and no-tillage), with or without biochar application (28 t ha-1) (short term and medium term effect) were analyzed. Over two years, emissions of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) were measured, and global warming potential (GWP), yield-scaled GWP (GWP-y), and net ecosystem carbon balance (NECB) were calculated under these different treatments: flooding with tillage (FST), sprinkler irrigation with tillage (SST), sprinkler irrigation without tillage (SSNT), and the corresponding biochar amendment treatments (FST-B, SST-B and SSNT-B). The results showed that flooding irrigation generated significant CH4 emissions (with a mean value of 350 kg CH4-C ha-1 across biochar and non-biochar treatments), while sprinkler irrigation acted as a sink of CH4 (mean value of-2.40 kg CH4-C ha-1). However, the transition from flooding to sprinkler irrigation, regardless of tillage systems, led to a significant increase in N2O emissions (whose values reached up to 10.7 N2O-N kg ha-1), which can be counteracted by biochar application (at both short or me<acute accent>dium term), to values statistically similar to those of permanent flooding. Furthermore, throughout the study, the lowest values of GWP-y was observed under SST-B treatment. In addition, biochar contributed to a further rise in the NECB, regardless of irrigation and tillage methods. Therefore, the implementation of sprinkler irrigation, especially under tillage system, with biochar represents a effective strategy to greehouse gas mitigation, as well as to enhance the C inputs into NECB of rice crop.