Optimizing water and nitrogen management to balance greenhouse gas emissions and yield in Chinese rice paddies

Context

Irrigation and fertilizer applications, the two most common practices to ensure high yield, affect almost all soil biogeochemical processes including greenhouse gas (GHG) emissions. How to balance irrigation and nitrogen application in farmland to synergize GHG emissions and crop yield is an inherent requirement for achieving sustainability, particularly in China rice paddy fields.

Objective

In this study, we first acquired data on GHG emissions and crop yield from rice field experiments worldwide under various irrigation and nitrogen application conditions. Subsequently, based on this dataset, we conducted modeling analysis using machine learning techniques to assess the optimization potential of irrigation and nitrogen fertilizer application in Chinese rice fields, aiming to achieve synergistic reductions in GHG emissions and improvements in crop yield under both historical and future climate scenarios.

Results and conclusions

The results indicated that the selected input features provided good predictive accuracy for rice yield and Global Warming Potential (GWP) in rice fields, with R² of 0.71 and 0.85, respectively. Furthermore, upon optimizing irrigation water usage in China rice fields to concurrently address GHG emissions and crop yield, the potential reductions in irrigation water were found to be −21.5 %, −29.1 %, and −13 % under past climate conditions, the SSP126 scenario, and the SSP585 scenario, respectively. After jointly optimizing both irrigation water and nitrogen fertilizer application, the reduction in irrigation water under past climate conditions, the SSP126 scenario, and the SSP585 scenario were −23 %, −31.4 %, and −16.9 % respectively. Correspondingly, the reductions in nitrogen fertilizer application were −22.9 %, −27.3 %, and −24.84 % for each scenario. Additionally, the study revealed a significant regional disparity between the northern and southern regions of China in these optimizations. Overall, southern China exhibits greater potential for irrigation water savings and rice yield increases compared to northern regions, while the potential for greenhouse gas emission reduction is higher in the north.

Significant

The findings provided both direction and quantifiable data support for the sustainable production of rice.