Mitigating greenhouse gas emissions by replacing inorganic fertilizer with organic fertilizer in wheat–maize rotation systems in China

Combining organic and inorganic fertilizer applications can help reduce inorganic fertilizer use and increase soil fertility. However, the most suitable proportion of organic fertilizer is unknown, and the effect of combining organic and inorganic fertilizers on greenhouse gas (GHG) emissions is inconclusive. This study aimed to identify the optimum ratio of inorganic fertilizer to organic fertilizer in a winter wheat–summer maize cropping system in northern China to achieve high grain yields and low GHG intensities. The study compared six fertilizer treatments: no fertilization (CK), conventional inorganic fertilization (NP), and constant total nitrogen input with 25% (25%OF), 50% (50%OF), 75% (75%OF), or 100% (100%OF) organic fertilizer. The results showed that the 75%OF treatment increased the winter wheat and summer maize yields the most, by 7.2–25.1% and 15.3–16.7%, respectively, compared to NP. The 75%OF and 100%OF treatments had the lowest nitrous oxide (N₂O) emissions, 187.3% and 200.2% lower than the NP treatment, while all fertilizer treatments decreased methane (CH₄) absorption (by 33.1–82.0%) compared to CK. Carbon dioxide flux increased in the summer maize growing season (by 7.7–30.5%) compared to CK but did not significantly differ between fertilizer treatments. The average global warming potential (GWP) rankings across two wheat–maize rotations were NP > 50%OF > 25%OF > 100%OF > 75%OF > CK, and greenhouse gas intensity (GHGI) rankings were NP > 25%OF > 50%OF > 100%OF > 75%OF > CK. We recommend using 75% organic fertilizer/25% inorganic fertilizer to reduce GHG emissions and ensure high crop yields in wheat–maize rotation systems in northern China.