Reducing the carbon intensity of crop production is an important component of sustainable agriculture, but management practices capable of mitigating greenhouse gas emissions (GHG) can have undesirable ecological and economic impacts. Intensive GHG emissions from flooded rice, for instance, can be substantially reduced through implementation of alternate wetting and drying cycles (AWD) during the growing season. However, adoption of this strategy in the U.S. has been slow due to farmer concerns over adverse yield impacts and increased resource demands. AWD can increase nitrogen (N) losses, induce water stress, and encourage weed proliferation. Determining strategies that avoid these adverse impacts is therefore paramount to encouraging widespread and successful implementation of GHG mitigation practices. The objective of our work is to evaluate the environmental and yield impacts associated with AWD in rice relative to continuous flooding (CF) and identify practices with the greatest potential for maintaining yields and minimizing adverse impacts. Using data aggregated by UCANR’s Agronomy Research Information Center for Rice, we modeled rice production under CF and five AWD schedules varying in the frequency and severity of dry-down events. We then determined the carbon intensity and pollutant loads associated with each production scenario using life cycle assessment models.
Results/Conclusions
Preliminary results indicate AWD can reduce yield-scaled GHGs by up to 40% under the range of scenarios simulated. Implementation of two moderately severe, mid-season dry-downs resulted in the lowest GHG emissions. Grain yield was relatively unaffected for moderate and severe but infrequent AWD scenarios. More frequent and severe schedules required increased herbicide and N inputs to achieve similar yields to CF. When these irrigation scenarios were simulated with sufficient N and herbicides to result in yields comparable to those achieved under CF, GHGs varied by only 8% across all AWD scenarios and were roughly 37% lower than those under CF. While these increased N and pesticide demands minimally impacted GHGs, they increased emissions to other air and water pollutants by ~10 – 25%. Together, our results suggest that AWD, when practiced with moderate and/or infrequent dry-down events, is a win-win management practice capable of maintaining yields and mitigating GHGs without contributing to additional adverse environmental impacts. Implementation of AWD schedules with high dry-down severity and frequency, however, can reduce yields, curtailing yield-scaled GHG mitigation. While additional agrochemical inputs can compensate for yield reductions with minimal impact on life cycle GHGs, these inputs come at economic and environmental costs.