Balancing non-CO2 GHG emissions and soil carbon sequestration in U.S.
rice paddies: implications for natural climate solutions
Abstract
The U.S. rice paddy systems play an increasingly vital role in ensuring
food security, which also contribute massive anthropogenic non-CO2 (CH4
and N2O) greenhouse gas (GHG) emissions with expanding cultivation area.
Yet, the full assessment of GHG balance, considering trade-offs between
soil organic carbon (SOC) sequestration and non-CO2 GHG emissions, is
lacking. Integrating an improved agricultural ecosystem model with a
meta-analysis of multiple field studies, we found that U.S. rice paddy
was a rapidly growing net GHG emission source, increased 138% to 8.88 ±
2.65 Tg CO2eq yr-1 in the 2010s. CH4 emission made the most significant
contribution (10.12 ± 2.28 Tg CO2eq yr-1) to this increase in net GHG
emissions in the 2010s, but increasing N2O emissions, accounting for
~2.4% (0.21 ± 0.03 Tg CO2eq yr-1), cannot be ignored.
SOC sequestration could offset about 14.0% (1.45 ± 0.46 Tg CO2eq yr1)
of the climate-warming effects of soil non-CO2 GHG emissions in the
2010s. The aggravation of net GHG emissions stemmed from intensified
land use/cover changes, rising atmospheric CO2, and heightened synthetic
N fertilizer and manure application. Climate change exacerbated around
~21% of soil N2O emissions and ~10% of
soil CO2 release in the 2010s. Nonetheless, adopting no/reduced tillage
resulted in a substantial decrease of ~10 % in net soil
GHG emissions, and non-continuous irrigation exhibited the potential to
mitigate around 39% of soil non-CO2 GHG emissions. Great potential for
emissions reduction in the mid-South U.S. by optimizing synthetic N
fertilizer and manure ratios, reducing tillage, and implementing
non-continuous irrigation.