Rice-fish systems (RFS, ‘fish’ refers to carp, crab, crayfish and turtle) have been widely practiced in China recently. Whether rice-fish systems would affect rice yield and soil fertility is concerned. In this study, we examined four types of RFS (Rice-carp, rice-crab, rice-crayfish, and rice-turtle) systems that account for about 80% of the total RFS area. We assessed the sustainability of these 4 types of RFSs via nationwide surveys of 86 farms (536 pairs of paddy fields) and a multi-year study conducted at four farms (4 randomized blocks at each farm’s experiment) in China, each pair and block consisted of an RFS field and a rice monoculture (RM) field. Rice yield was measured as air-dried weight, and fish yield was measured as fresh weight. The temporal stability of rice yield (S) was compared for 7 years (2012–2018). The application of nitrogen fertilizers was recorded in each surveyed farm. Soil samples were collected and determined soil organic matter (SOM), total nitrogen (N), total phosphorus (P) and the total amount of reducing substances.
Results/Conclusions
The nationwide field survey showed that rice yields in RFSs (6-10 tons ha-1) were equivalent to or greater than rice yields in RMs, and simultaneously produce aquatic fish (0.64-2.18 tons ha-1). This nationwide field survey showed that fertilizer -N input was 11-62% lower in the RFSs than in the corresponding RMs. The multi-year field experiment showed that the temporal stability of rice yield was higher under RFSs than under RMs. Although fertilizer-N input was lower in RFSs, soil fertility in RFSs, indicating in SOM, total N and total P, was similar to that in RMs under both field survey and field experiment. This result can be explained by the complementary use of feed-N between rice and fish. The total amount of reducing substances in the soil was higher in the rice-crayfish RFSs than in the RMs. In the other RFSs, which are not flooded in winter, the amount of reducing substances was similar in RFSs and RMs. The above results indicated that rice-fish systems can maintain yield and soil fertility with low fertilizer input.