The Utilization Of Nutrients In Traditional Rice-fish Go-culture System

Modern agriculture has greatly increased global crop yields. However, the over use of modern crop varieties has resulted in a decrease of crop species and genetic diversity in agricultural system. The intensified use of agrochemicals and fertilizers also produced some negative effects such as environmental pollution. The shortage of modern agriculture requires "rethinking agriculture" and learning back from traditional agricultural systems. Rice-fish co-culture system, be practiced by local farmers for over 1200 years in south Zhejiang province, China, is one of the outstanding traditional agricultural systems in the world. In 2005, this specific rice-fish co-culture was identified by FAO and UNDP as one of the five "globally important agricultural heritage system, GIAHS". This study is to examine how the nutrients are utlized in rice-fish co-culture. The results are as follows:1 The utlization of nutrients in rice-fish co-cultureIn this experiment, total nitrogen (TN), total phosphorus (TP), total ammonia nitrogen (NH4-N) and chemical oxygen demand (COD) in the field water were significant higher in fish monoculture system (FM) than that in rice-fish co-culture system (RF) when the fish stocking density of these two systems was the same. These results indicated that the presence of rice reduced nutrient loss and promoted nutrient use efficiency. The contained N in rice is significantly higher in rice-fish co-culture (RF) than that in rice monoculture (RM), which imply that stocking fish in paddy field can increase rice intake of nitrogen.2 The utlization of nutrients in rice-fish coculture with higher density of fish stockingNo significant differences of TN, TP, NH4+-N and COD were found in the field water between RF and RM under low stocking density, but these parameter values were significantly higher in RF than that in RM under high stocking density. These results suggested that improving the productivity of this system may resulted in negative effects on environment.3 Effects of fish feeds and chemical fertilizers on nutrient-use in rice-fish co-cultureA field experiment with three treatments was set up to test the effects of fish feed-N and chemical fertilizer-N on utilization of nutrints. The three treatments were RFa (fertilizer-N 195kg/ha; feed- N 30kg/ha), RFb (fertilizer-N 175.5kg/ha; feed-N 49.5kg/ha) and RFc (fertilizer-N 157.5kg/ha; feed-N 67.5kg/ha) respectively. The total N input (including fertilizer-N feed- N 225kg/ha) was the same in the three treatments. The results showed that TN, TP, NH4+-N and COD in field water were positively correlated to feed-N input. Nutrients maintaining in the environment increased with feed-N increaseing. Experiment also showed that N contained in fish and rice increased with fertilizer-N and feed-N increasing. The efficiency of N utilization was significantly higher in RFc than other treatments.4 Effects of types of fish feed on nutrient use in rice-fish co-cultureFour types of fish feeds (compound formula feed, puffing compound formula, local fish feed and 50% compound formula+50% local fish feed) were used in this experiment to test whether types of fish feed affect the efficiency of N use in rice-fish coculture. The results showed that fish yield, efficiency of total N use. efficiency of feed N use and conversion rate of fish feed were significantly higher in treatment puffing compound formula than other treatments. Using puffing compound formula in rice-fish coculture could increase fish and yields, also reduced N staying in the environment.