Split N and P addition decreases straw mineralization and the priming effect of a paddy soil: a 100-day incubation experiment

The effect of mineral fertilization and its application pattern on microbial activity and the subsequent CO₂ and CH₄ emissions arising from soil organic matter (SOM) or added substrate remains unclear. We quantified the decomposition of ¹³C-labeled straw and the priming effect (PE) governed by the N and P fertilizer application pattern during a 100-day experiment in a flooded soil. Straw addition increased the total CO₂ and CH₄ emissions. Straw mineralization increased by 30% and decreased by 19% after full and split NP application, respectively, compared with only straw addition. However, application of NP fertilization (full or split) inhibited straw-derived CH₄ emissions compared with only straw addition. SOM decomposition was increased by straw addition, yielding a positive PE for CO₂ emission. The application of split NP fertilization along with straw addition improved microbial activity, yielding the highest positive PE for CO₂ emission. In contrast, compared with the control (no addition), split NP application decreased the positive PE for CH₄ emission. Therefore, the straw-C-derived total CO₂ equivalent emission was decreased by split NP application. These results were mainly attributable to the increased Olsen P, microbial biomass, enzyme activity, and straw-derived C microbial use efficiency of split NP application, which negatively affected the PE for CH₄ emission; this was supported by the results of standardized total effects determined from structural equation models. Overall, compared with full application, split NP fertilizer application significantly decreased the straw-C mineralization rate and PE for CH₄ emission, thereby mitigating greenhouse gas emission and SOM storage in paddy soil.