Objective The aim was to explore the effects of high nitrogen organic material- Myriophyllum aquaticum (M. aquaticum) addition on soil carbon and pH.

Method The effects of M. aquaticum (M), rice straw (R), and a combination of both, M. aquaticum and rice straw (MR) added to the soil on soil pH, dissolved organic carbon (DOC), soil organic carbon (SOC) and microbial biomass carbon (MBC) were examined and their correlations were analyzed.

Results ① After the addition of organic materials, the contents of DOC, SOC and MBC were significantly increased in weakly acidic soil. Meanwhile, the most pronounced increase in DOC observed in the M. aquaticum treatment, which increased by 18.25% and 21.09% compared to rice straw application alone and the mixed treatment, respectively. ② SOC content was significantly increased for all treatments in strongly acidic soil. Compared with straw and the mixed treatment, soil DOC contents were significantly increased by 26.48% and 34.33% for the M. aquaticum treatment, respectively. ③The soil pH was significantly increased with M. aquaticum addition treatment in both acidic soils, particularly in strongly acidic soil, which could raise soil pH from 4.89 to 6.02. These were increased 6.34% and 8.88% higher than that with straw alone and the mixed treatments, respectively. ④ The correlation analysis showed a significant positive correlation between soil pH and DOC in strongly acidic soil, while a significant negative correlation was observed between MBC and pH in weakly acidic soil.

Conclusion The application of M. aquaticum as a high-nitrogen organic material could significantly promote soil carbon and improve soil pH in acidic soils, showing that it could be a high-quality organic fertilizer for farmland to facilitate the resource re-utilization of agricultural waste.