Estimation of N2O and CH4 emissions in field study and DNDC model under optimal nitrogen level in rice-wheat rotation system

Abstract

The rice-wheat rotation system in the lower-and-middle section of the Yangtze River Basin plays a crucial role in ensuring China's food security, contributing significantly to the nation's grain production. However, in recent years, the overuse of nitrogen fertilizers to boost yields has led to growing environmental concerns, particularly with respect to greenhouse gas (GHG) emissions, such as nitrous oxide (N₂O) and methane (CH₄). To optimize the management of the rice-wheat system and ensure the attainment of the goal of greenhouse gas emission reduction without compromising crop yields, in this study, we combined field experiments and DNDC model to estimate comprehensively the economic and reduced-emission benefits. Our results showed that N₂O emissions increased significantly as nitrogen application rose, demonstrating a positive linear relationship between nitrogen input and N₂O release. However, CH₄ emissions followed a more complex trend, initially decreasing and then rising as nitrogen increased, likely due to the intricate interactions between soil nitrogen availability, organic matter decomposition, microbial processes and plant growth. The DNDC model simulation exhibited a high degree of accuracy in predicting crop yields and N₂O emissions, particularly at higher nitrogen application levels. However, the model's performance was less reliable for lower nitrogen application scenarios and for simulating CH₄ emissions, suggested further refinement of the model's underlying mechanisms is required. Based on field data and simulation results, this study identified an optimized fertilization strategy for reducing GHG emissions while maintaining crop productivity. By reducing nitrogen application rates to 223 kg N ha for wheat and 222 kg N ha for rice, and controlling the straw return to 10 %, which might be possible to significantly lower N₂O and CH₄ emissions without yield loss and input cost. This strategy would offer a potential practice for balancing agricultural productivity with environmental sustainability, promoting the development of low-carbon farming practices in the region and contributing to the global effort to mitigate climate change.