Abstract:
Few studies have explored greenhouse gas (GHG) emissions from arable land in subSaharan Africa (SSA), and particularly from rice paddy fields, which can be a major source of methane
(CH4
) and nitrous oxide (N2O) emissions. This study examined the effect of drainage on CH4 and
N2O emissions from rice fields in Rwanda under shallow drainage to 0.6 m, with the drain weir open
four times per week, and deep drainage to 1.2 m with the weir open four times or two times per week.
CH4 and N2O fluxes from the soil surface were measured on nine occasions during rice flowering
and ripening, using a closed chamber method. Measured fluxes made only a minor contribution
to total GHG emissions from rice fields. However, drainage depth had significant effects on CH4
emissions, with shallow drainage treatment giving significantly higher emissions (~0.8 kg ha−1 or
~26 kg CO2
-equivalents ha−1
) than deep drainage (0.0 kg) over the 44-day measurement period. No
treatment effect was observed for N2O fluxes, which ranged from low uptake to low release, and were
generally not significantly different from zero, probably due to low nitrogen (N) availability in soil
resulting from low N fertilization rate (in the region). Overall, the results suggest that deep drainage
can mitigate CH4 emissions compared with traditional shallow drainage, while not simultaneously
increasing N2O emissions
