UC Davis

CONTEXT Manure recycling to cropland reduces synthetic fertilizer use and nitrogen (N) waste while increasing soil carbon (C) sequestration, which is important for sustainable crop production. However, few studies have systematically integrated long-term N budgets with changes of soil C and N stocks and the greenhouse gas (GHG) balance. OBJECTIVE We aim to quantify the long-term responses of crop productivity, changes of soil C and N stock, reactive N losses and the GHG balance to various C and N management practices, thus providing evidence for sustainable crop production. METHODS We used a 15-year wheat-maize double cropping system in the North China Plain. The experiment included eight fertilization treatments with contrasting C and N management practices. Crop productivity, N losses, changes of soil C and N stock; and the GHG balance were evaluated. RESULTS AND CONCLUSIONS Compared with conventional fertilization with excess synthetic N, long-term balanced organic and synthetic N fertilization (in which N rates were determined using an N balance approach and target N yield, and the rates of synthetic N equal to the difference between above N rate and mineralized N from manure) increases crop yield and N harvest by 8–11%, and soil C and N sequestration by 191–230%, while reducing N inputs by 23%, thus also reducing reactive N losses by 40% and the GHG balance from 59 to −2143 kg CO2-eq ha−1. Although the N surplus was relatively high in the balanced organic and synthetic N fertilization, it did not cause high N losses but achieved high soil C and N sequestration and crop yield, which were not achieved under the optimum synthetic N fertilization. SIGNIFICANCE This study emphasizes the benefits of combining organic and synthetic N within an appropriate N management framework, offering a global model for sustainable crop production in croplands. Site-specific adjustments could be necessary when applying these findings to other regions with distinctly different soil or climatic conditions. We should interpret N surplus cautiously because a high N surplus does not necessarily lead to high N losses with manure recycling to croplands.