  Flooded rice production is crucial to global food security, but there are
associated environmental concerns. In particular, it is a significant source of
methane and nitrous oxide emissions and a large consumer of water resources,
while arsenic, cadmium and lead levels in the grain are a serious health
concern. There is also a tendency to use more organic fertilisers to close
nutrient cycles, posing a threat of even higher greenhouse gas emissions and
grain arsenic levels. It has been shown that alternate wetting and drying (AWD)
water management reduces both water use and greenhouse gas emissions, but
success at maintaining yields varies. This study tested the effect of early AWD
(e-AWD) versus continuous flooding (CF) water management practices on grain
yields, greenhouse gas emissions and grain arsenic, cadmium and lead levels in
a split plot field experiment with organic fertilisers under organic
management. The e-AWD water regime showed no difference in yield for the
organic treatments. Yields significantly increased by 5 to 16 percent in the
combination treatments. Root biomass and root length increased in the e-AWD
treatments up to 72 and 41 percent, respectively. The e-AWD water regime
reduced seasonal methane emissions by 71 to 85 percent for organic treatments
and by 51 to 76 percent for combination treatments; this was linked to a 15 to
47 percent reduction in dissolved organic carbon. Nitrous oxide emissions
increased by 23 to 305 percent but accounted for less than 20 percent of global
warming potential. Area and yield scaled global warming potentials were reduced
by 67 to 83 percent. The e-AWD regime altered soil redox potentials, resulting
in a reduction in grain arsenic and lead concentrations of up to 66 % and 73 %
respectively. Grain cadmium levels were also reduced up to 33 % in organic
treatments.
