Identifying rice varieties for mitigating methane and nitrous oxide emissions under intermittent irrigation.

CONTEXT OR PROBLEM

Most of the research evaluating rice varieties, a major global staple food, for greenhouse gas (GHG) mitigation has been conducted under continuous flooding. However, intermittent irrigation practices are expanding across the globe to address water shortages, which could alter emissions of methane (CH) compared to nitrous oxide (NO) for reducing overall global warming potential (GWP). To develop climate-smart rice production systems, it is critical to identify rice varieties that simultaneously reduce CH and NO emissions while maintaining crop productivity under intermittent irrigation.

OBJECTIVE

This study assessed CH and NO emissions, grain yield, and GWP of four rice varieties cultivated under intermittent irrigation in Colombia.

METHODS

Four common commercial rice varieties were evaluated over two seasons-wet and dry in 2020 and 2021-in two Colombian regions (Tolima and Casanare).

RESULTS

Wet-season crop productivity was similar among varieties. However, F68 in Tolima and F-Itagua in Casanare significantly reduced yields in the dry season, likely due to periods of crop water stress. Overall, CH emissions and GWP were relatively low due to frequent field drainage events, with GWP ranging from 349 to 4704 kg CO equivalents ha. Accordingly, NO emissions contributed 73% to GWP across locations, as wet-dry cycles can increase NO emissions, creating a tradeoff for GWP when reducing CH through drainage. Varieties F67 in Tolima and F-Itagua in Casanare significantly reduced GWP by 32-61% across seasons, primarily by decreasing NO rather than CH emissions.

CONCLUSIONS

Rice varietal selection achieved significant GWP mitigation with limited impacts on grain yield, mainly due to reduced NO emissions under non-continuously flooded irrigation.

IMPLICATIONS/SIGNIFICANCE: This research underscores the critical role of rice varietal selection in addressing global climate-change and water-scarcity challenges, which drive the adoption of intermittent irrigation practices. By focusing on reducing N₂O emissions through appropriate variety selection, this study provides valuable insights for rice systems worldwide that are adapting to these pressing environmental challenges.