Ecological legacy in the agricultural heritage rice-fish co-culture system

Background/Question/Methods Modern agriculture now faces challenges in producing sufficient food while minimizing its negative environmental effects, and therefore requires “rethinking”. Such rethinking should include reconsideration of traditional agricultural systems, which have contributed to food and livelihood security throughout the world for centuries. Recognizing the ecological legacy in the traditional agricultural systems may help us develop novel methods of sustainable agriculture. Here, we describe how rice-fish co-culture, a "globally important agricultural heritage system”,, has been maintained for over 1200 years in south China. We first conducted a 6-year field survey to assess and compare the ecosystem stability of rice monoculture (RM) and rice-fish co-culture (RF). We then conducted a 5-year field experiment to determine the mechanism of the stability in RF. We compared three treatments without pesticide application: RM, RF, and fish monoculture (FM). We measured rice yield (in RM and RF) and fish yield (in RF and FM), occurrence of rice pests in RM and RF and the interaction between rice and fish in RF. We conducted another field experiment to determine how RF can maintain the same yield stability as RM with a low input of chemical fertilizers. We examined the fate of applied N in RM, RF, and FM.

Results/Conclusions We found that RF maintained the same rice yield and stability as RM but required 68% less pesticide and 24% less chemical fertilizer than RM. The first experiment confirmed that the temporal stability of rice yield is higher in RF than in RM in the absence of pesticide application. We found that this higher stability of rice yield in RF is associated with the reduction of insect pests, diseases, and weeds. The 26% of reduction in rice planthoppers was partly due to fish activity. The second experiment found that the reduced input of N fertilizer in RF can be explained by complementary N use by rice and fish. A comparison of RF with and without fish feed indicated that 32% of the N contained in rice grain and straw was from fish feed. The comparison of RF and FM indicated that 2.1% of the fertilizer-N was assimilated into fish bodies in RF. Our results suggest that modern agricultural systems might be improved by adding species to monocultures that result in positive interactions and complementary use of resources.