Fig. P1.

Positive interactions and complementary use of nitrogen (N) between rice and fish explain why the rice–fish coculture system maintains productivity for long time periods with low input of chemicals. (A) Positive interactions between rice and fish: Fish remove pests from rice through feeding activity, while rice plants moderate the field environment for fish, which in turn promotes fish activity and pest removal. (B) Complementary use of N by rice and fish: Unused fertilizer N promotes plankton in paddy fields that is consumed by fish. The unconsumed fish feed acts as an organic fertilizer, with the N in the unconsumed feed being gradually used by the rice. Thus, rice and fish use different forms of N, resulting in a high efficiency of N utilization in RF.