Effects of long-term low-input rice-fish co-culture on soil nutrient cycling and organic carbon pool stability

Objective To investigate the changes in soil organic carbon pool, nutrient stoichiometric ratios and so on under a long-term low-input rice-fish co-culture system, deeply analyze the carbon pool dynamics in the rice-fish system, and enhance its ecological functions.

Method The study focused on the long-term low-input rice-fish co-culture system in Chenxi County, a representative county of traditional rice-fish co-culture in Hunan. The changes in soil nutrient content, physical-chemical property, nutrient storage, organic carbon component, stoichiometric ratio and carbon pool indexes within the rice-fish co-culture systems, which have been in operation for 15 years (RF15) and 50 years (RF50), were analyzed, and the key influencing factors were explored.

Result Compared to rice monoculture (RM), RF15 showed significant reductions in soil organic carbon/total nitrogen/total phosphorus/nitrate nitrogen/ammonium nitrogen/available phosphorus contents, organic carbon storage/nitrogen storage/phosphorus storage, readily oxidized organic carbon content and its proportion in organic carbon; The C∶N, pH, particulate organic carbon content and its proportion, mineral-associated organic carbon content proportion, carbon pool activity, and carbon pool activity index increased significantly by 47.98%, 13.15%, 35.47%, 72.24%, 31.68%, 58.07%, and 58.07%, respectively. FR50 experienced significant increases in total nitrogen content, C∶P, N∶P, and nitrate nitrogen content by 13.13%, 33.08%, 14.31%, and 51.52%, respectively, while total phosphorus content, volume weight, organic carbon storage, phosphorus storage, readily oxidized organic carbon content, mineral-associated organic carbon content and its proportion decreased significantly. The carbon pool management indexes in RF15 and RF50 remained stable overall, and were both greater than 100. Under the long-term rice-fish model, the environmental factors significantly related to the stability index of soil organic carbon pool were total nitrogen content, C∶N, and organic carbon storage.

Conclusion Although the low-input rice-fish co-culture system may lead to nutrient loss, the extended self-maintenance of the system enables it to recover nutrient storage autonomously. Long-term rice-fish co-culture can improve soil quality, and improve the ecological environment of rice field. The findings provide a theoretical basis for optimizing the rice-fish co-culture system, which could help enhance its ecological functions and sustainability.