The environmental and agronomic benefits and trade-offs linked with the adoption alternate wetting and drying in temperate rice paddies

Context

Alternating wetting and drying (AWD) is an irrigation practice, alternative to continuous flooding, to improve the agro-environmental sustainability of rice cultivation. Benefits include reduction in water consumption, methane (CH₄) emissions and arsenic (As) concentrations in grain. However, drainage periods during AWD can negatively affect nitrogen (N) use efficiency by the crop and grain yields, while increasing nitrous oxide (N₂O) emissions and cadmium (Cd) contents in grain.

Objective

The objective of this study was to provide a holistic evaluation of AWD adoption in temperate rice cropping systems, including associated trade-offs. We hypothesized that the adoption of AWD in water seeded rice paddies can reduce the global warming potential (GWP) without affecting plant N uptake or introducing yield gaps, and also maintain a high quality of rice grain by limiting the uptake of metal(loid)s present in the soil, thereby resulting in an overall positive agro-environmental performance.

Methods

In a two-year field experiment in NW Italy two alternative irrigation practices involving water seeding followed by AWD management of different severity (AWD_safe and AWD_strong) were evaluated relative to the conventional water seeding and continuous flooding (WFL), comparing three different rice varieties. Yields and yield components, plant N uptake, apparent N recovery (ANR), metal(loid) concentrations in grain, and CH₄ and N₂O emissions were evaluated.

Results

AWD_safe and AWD_strong maintained or increased yields compared to WFL depending on varieties, despite an increase in sterility. There were no consistent differences in N uptake and ANR. Both AWD_safe and AWD_strong significantly reduce As concentration in grain, but significantly increase Cd and nickel (Ni). AWD_safe and AWD_strong reduced CH₄ emissions by 45–55 % and 40–73 %, respectively, compared toWFL, while no increase in N₂O emissions was observed. This resulted in a reduction in the GWP of 46 and 54 % with AWD_safe and AWD_strong, respectively.

Conclusions and Implications

AWD was shown to be effective for mitigating GHG emissions from temperate rice cropping systems while maintaining high yield performance comparable or higher than WFL. AWD may represent a viable alternative to continuous flooding to improve agro-environmental sustainability of temperate rice cropping systems, but the trade-off between decreasing As and increasing Cd and Ni contents in the grain may represent an important concern for food safety with the adoption of this alternative water management practice.