Rice-soft shell turtle coculture effects on yield and its environment

• Yields and environmental quality in rice–turtle coculture (RT) were tested.
• Turtle and rice yields in RT were similar to those in turtle monoculture (TM) and rice monoculture (RM).
• N and P increased in field water and soil in TM but not in RT or RM.
• Only about 20% of feed-N and 23% of feed-P were assimilated by turtles.
• The unconsumed feed-N and -P were used by rice plants in RT.

Although traditional rice-fish farming (involving extensive aquaculture and low fish yields) can supply food and protect the environment, the economic viability and environmental effects are unknown for intensive rice-aquaculture systems that use high quantities of feed to produce high fish yields. Here, we studied an intensive, soft-shelled turtle (Pelodiscus sinensis) farm to determine whether an intensive rice-turtle system can produce high yields of turtle and rice without negatively affecting water and soil quality. Using a 6-year field survey and a 2-year field experiment, we compared the three production systems: rice monoculture (RM), rice-turtle coculture (RT), and turtle monoculture (TM). The field survey indicated that turtle yield did not significantly differ between RT and TM, and that rice yield did not significantly differ between RM and RT. The field survey also showed that soil nitrogen (N) and phosphorus (P) were increased in TM but not in RT even though the same quantities of N and P were applied to TM and RT. In the field experiment, yields were similar for rice in RT vs. RM and were similar for turtles in RT vs. TM. Levels of N and P in field water were significantly higher in TM than in RT or RM. At the end of the field experiment, N and P levels in soil had significantly increased in TM but not in RM or RT. Only 20.4% of feed-N and 22.8% of feed-P were used by turtles in TM, resulting in large quantities of feed-N and feed-P remaining in the environment. In RT, however, some of the feed-N and -P that was unused by turtles was taken up by the rice plants. The results suggest that integrating intensive turtle aquaculture with rice culture can result in high yields and low environmental impacts.