Ecosystem Functioning Of Species Interactions In Farming System

Modern agriculture has greatly increased global crop yields which mainly resulting from the greater inputs of chemical fertilizers and pesticides, new crop strains and other technologies of the "Green Revolution", but the continuous and heavy application of chemical fertilizers and pesticides has negatively affected the environment, induced pests resistant to pesticides and raised the costs of agriculture. The shortage of modern agriculture requires "rethinking agriculture" and learning back from traditional agricultural systems. Rice-fish co-culture system, practiced by local farmers for over1200years in south Zhejiang province, China, is one of the outstanding traditional agricultural systems in the world. In2005, this specific rice-fish co-culture was identified by FAO and UNDP as one of the five "globally important agricultural heritage systems, GIAHS". The main aim of our present study is to estimate the ecosystem stability of this rice-fish co-culture, and to examine how this co-culture system maintains the stability. We hypothesis that a co-evolutionary positive interaction between species (rice and fish, a nontrophic interaction) may generate multi-functioning of ecosystem and lead this ancient rice-fish co-culture still viable today with lower chemical application. The study was conducted at the GIAHS pilot site of the rice-fish system in China.1Temporal stability of rice yield and pesticides use in rice-fish co-cultureThrough household assessments in farmer's field, we found that no significant difference of rice yield between rice monoculture (RM) and rice fish co-culture (RF), but annual pesticide utilization was significantly higher in RM than that in RF during the study. Temporal stability (S) of rice yield was the same in RF and in RM, but pesticides application was greater in RM than RF. Temporal stability (S) of rice yield among samples in RM but not in RF was significantly positively dependent on pesticides. In our experiment without pesticide application, both rice yield and temporal stability (S) of rice yield were higher in RF than in RM over the5field experimental years. 2Occurrence of rice pests in rice-fish co-cultureData from light-trap survey showed that the population of rice planthoppers was higher in RM than that in RF, specifically in2006when rice planthoppers were outbreak. Field experiment showed that although density of some insect pests and diseases (e.g. rice case worm, rice false smut) did not reduce, the density of rice planthoppers, incidence of rice sheath blight and biomass of weeds significantly reduced by44.74%,54.35%and93.75%respectively due to fish presented in rice field.3Positive interactions between rice and fishOur field experiment showed that rice and fish can help each other in rice-fish co-culture system. On one hand, fishes create optimum environment for rice by removing insect pests, diseases and weeds. Active hitting behavior of fish on rice stem could explain26.04%reduction of rice planthopper. On the other hand, rice had a substantial positive impact on activities of fishes. First, rice creates an optimum environment for fish by providing shading and reducing field water temperature during the hot season. Compared to fish monoculture without rice (FM), water temperature and light intensity of water surface in RF reduced2.56℃and1456.29μmol m-2s-1around12:00-14:00. This ameliorated environment resulted in that the frequency of fish activity was57.6%higher in RF than that in FM. Second, rice acts as a nitrogen sink and helps reduce the ammonia (some of them excreted by the fish) in water and total N accumulated in soil, making the water cleaner for fish.4Nitrogen fertilizer application and Nitrogen use efficiencyIn our experiment, rice yield was significantly higher in rice-fish with feed input than that in rice-fish without feed applied and rice monoculture (RM) with36.51%higher N application. Fish feed input significantly increased fish yield in both fish monoculture and rice-fish co-culture. In RF and FM, only11.10%and14.20%contained N in fish feed was transferred into fish body respectively. In RF, however, rice plants can use the unconsumed N, resulting in less fish feed-N remaining in environment (e.g. soil or water). Compared to RF without fish feed application,31.84%N contained in rice grain and straw were from fish feed.5Traditional rice varieties conserved in rice-fish co-culture systemOur survey showed that small areas of traditional rice varieties were planted with hybrid varities. Only19%of the farmers who practiced rice monoculture planted traditional varieties while52%of farmers who practiced rice-fish co-culture planted traditional varieties. Traditional varieties represented13%of the total land planted to rice in the rice-fish system but only2%in the rice monoculture system. Our field experiment showed that in the rice-fish system without pesticides, rice planthopper numbers and sheath blight incidence were lower from traditional varieties than the hybrid varieties; no significant difference of rice yield was found between the traditional varieties and the hybrid varieties. Our results suggested that traditional rice varieties can be preserved through conserving GIAHS rice-fish co-culture.