Coupled incorporation of maize (Zea mays L.) straw with nitrogen fertilizer increased soil organic carbon in Fluvic Cambisol

Soil organic carbon (SOC) level is influenced by incorporation of crop straw and application of nitrogen (N) fertilizer, which are typical farming practices in intensive agricultural regions. However, the interaction between the N fertilization and crop straw incorporation on SOC levels is still not univocally established, especially for calcareous soils. We therefore conducted a 224-day laboratory incubation experiment with four levels of 13C-labeled maize straw amendment (0, 1 ×, 3 × and 5 × of maize straw yield) and three N fertilization rates (0, 300, and 600 kg N ha− 1 a− 1) on a Fluvic Cambisol to investigate the short-term response of SOC content. The 13C-labeled straw allowed partitioning of the CO2 produced from native SOC or crop straw for application to a two-compartment exponential decay model to simulate the addition of new SOC from the straw and the decomposition of the native SOC. The addition of maize straw caused immobilization of inorganic N during the incubation. Increased mineral N fertilization significantly inhibited the decomposition of maize straw, which led to the increased new SOC from maize straw amendment. Priming effect (PE) of native SOC decomposition peaked at 40 days after incubation, and then decreased until the end of the incubation. N fertilization significantly enhanced the cumulative PE when maize straw was not added (N2 induced PE at C0 was + 19% of C0N0 SOC decomposition), but had no significant effect when the highest rate maize straw was amended (N2 induced PE at C5 was 8% of C0N0 SOC decomposition), indicating that maize straw amendment can moderate the PE promoted by N fertilization. There was a positive linear correlation between the cumulative PE and the input of maize straw C. An increase in maize straw incorporation with N fertilization caused the largest increase in total SOC content at the end of 224-day incubation (the highest 23.7% for C5N2 treatment, i.e., 5 × maize straw yield + 600 kg N ha− 1 a− 1). Our findings highlight that in intensively managed agricultural regions, integrating N fertilization with crop residue amendment can promote SOC sequestration and the retention of fertilizer N in the soil. The results are particularly relevant for developing new or improved farming methods in areas with calcareous soils, such as northern China.