Nonlinear dependency of N2O emissions on nitrogen input in dry farming systems may facilitate green development in China

China's green development has advanced national strategic requirements for excessive nitrogen application, greenhouse gas emission reduction, and efficient production in food systems. However, large challenges still exist in achieving these goals. In this study, a comprehensive meta-analysis and random forest identification were conducted to integrate nitrogen fertilization based nitrous oxide (N2O) emission data from field experiments in the dry farming system of China (DFSC), and to analyze the dependency of N2O emissions and crop yield on nitrogen inputs. We then quantified the potential reasonable nitrogen dose in the DFSC that would simultaneously reduce N2O emissions and favor China's green development. The results showed an absolute impact of nitrogen input on N2O emissions, and a significant nonlinear response between N2O emissions and nitrogen dose in the DFSC. However, the crop yield exhibited a different pattern: yields of cereal and cash crops in response to nitrogen input were modeled by a quadratic polynomial, especially at extremely high nitrogen rates (>300 kg N ha(-1) for cereals and >600 kg N ha(-1) for cash crops). The yield enhancing effect tended to be flat or even decrease. We propose to achieve a reasonable nitrogen dose by reducing the 1/3 nitrogen surplus in the DFSC, according to the various soil-climatic conditions. For cereal, cash, vegetable, tea and orchard crops, the values should be 98.72 - 133.46, 67.66 - 107.4, 258.53 - 470.57, 159.61-296.09 and 269.08-383.48 kg N ha(-1), respectively. The findings of our investigation indicate that implementation of a reasonable nitrogen dosage will not give rise to a large yield decrease and will better contribute to meeting the requirements of N2O mitigation and a national green development strategy.

Automated summary

China's green development emphasizes the need for reduced nitrogen application, greenhouse gas emission reduction, and efficient food production. However, challenges remain in achieving these goals. Research in China's dry farming system revealed a strong impact of nitrogen input on N2O emissions, with a significant nonlinear relationship between N2O emissions and nitrogen dose. By reducing nitrogen surplus, a reasonable nitrogen dose can be achieved without significantly decreasing crop yield, contributing to N2O mitigation and national green development goals.