Reducing greenhouse gas emissions and grain arsenic and lead levels without compromising yield in organically produced rice

TL;DR

This study demonstrates that early alternate wetting and drying (e-AWD) water management in organic rice farming significantly reduces greenhouse gas emissions and grain toxic metal levels without compromising yield, offering an environmentally sustainable practice.

Contribution

It provides evidence that e-AWD effectively decreases methane emissions and grain arsenic and lead levels in organic rice cultivation, with minimal impact on yield.

Findings

Methane emissions reduced by up to 85% with e-AWD.

Grain arsenic and lead levels decreased by up to 66% and 73%.

Yield remained unaffected by e-AWD in organic treatments.

Abstract

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.