Impacts Of Feeding Strategy On Gaseous Nitrogen Emission And Feed Nitrogen Utilization Of Rice-Fish Co-culture System

Eutrophication is one of the key factors restricting the rapid development of pond aquaculture.Rice-fish co-culture is a typical ecological farming model in our country,which has unique advantages in terms of complementary utilization of nutrients and reduction of nitrogen pollution.Feed strategy（feeding rate and feed protein content）is the key parameter that determines the nitrogen input in the rice-fish co-culture system,which directly affects the growth of fish and the emission of nitrogen pollutants in the system.However,the effects of feeding rate and feed protein content on gaseous nitrogen emissions and feed nitrogen utilization in rice-fish co-culture systems are still lacking in in-depth research.To this end,this study took the yellow catfish ponds to grow rice as an example,a simulation experiment was conducted to investigate the impact of feeding strategy on the N₂O and NH₃ emission characteristics,nitrogen contents in the water and soil,growth performance of yellow catfish（Pelteobagrus fulvidraco）,and feed nitrogen utilization of the rice-yellow catfish co-culture system,to provided theoretical references for the use of feeding rate and feed protein content in the rice-yellow catfish co-culture system.The main results of this study are as follows:1.The increase in the feeding rate will promote the N₂O emission in the rice-yellow catfish co-culture treatment,and has no significant effect on NH₃ volatilization.In the rice-yellow catfish co-culture treatment,the non-feeding treatment showed a net N₂O absorption state(-0.01 kg·ha^-1),while the feeding rate of 2%(0.11 kg·ha^-1)and the feeding rate of 4%(0.19 kg·ha^-1),6%feeding rate(0.33 kg·ha^-1)and 8%feeding rate(0.72 kg·ha^-1)were treated as net N₂O emissions.Under the conditions of the same feeding rate,the N₂O emissions of the rice-yellow catfish co-culture treatment were significantly reduced by 32.10%compared with the yellow catfish monoculture.The content of total nitrogen,ammonium nitrogen,nitrate nitrogen and nitrite nitrogen in the water body in the treatment of rice-yellow catfish co-culture increased with the increase of feeding rate,indicating that the increase in feeding rate will weaken the mitigation effect of rice-yellow catfish co-culture system on N₂O emissions and nitrogen pollution in water bodies.2.The increase in feeding rate can promote the growth performance of yellow catfish.The specific growth rate,crude protein content and protein gain of yellow catfish increased first and then decreased with the increase of feeding rate;the utilization rate of feed nitrogen of yellow catfish showed a downward trend with the increase of feeding rate.Regression analysis results showed that the maximum specific growth rate of yellow catfish,the maximum increase in protein gain,and the minimum N₂O emission per unit yield corresponded to feeding rates of 5.49%,5.16%,and 1.00%,respectively.Combining with actual production,under the premise of ensuring the growth performance of yellow catfish,reducing N₂O emissions per unit yeild as much as possible,it is recommended that the feeding rate of the rice-yellow catfish co-culture does not exceed 5.49%.3.The increase of feed protein content will promote the N₂O emission in the rice-yellow catfish co-culture treatment,and has no significant effect on NH₃ volatilization.The content of total nitrogen,ammonium nitrogen,nitrate nitrogen and nitrite nitrogen in the water body in the treatment of rice-yellow catfish co-culture increased with the increase of feed protein content.The N₂O emission and water nitrogen content of the rice-yellow catfish co-culture treatments fed the same feed were significantly lower than that of the yellow catfish monoculture treatment.4.The increase of feed protein content can promote the growth performance of yellow catfish in the rice-yellow catfish co-culture.Regression analysis shows that when the feed protein content is 25.00%-37.07%,the growth performance and N₂O emission per unit yeild of yellow catfish increased with the increase of feed protein content,while further increasing the feed protein content has no significant effect on the growth of yellow catfish.Taking into account the N₂O emission factors,the protein content for rice-yellow catfish co-culture should be as low as 37.07%.5.Feed protein content has a significant effect on ammonia excretion and digestive enzyme activity of yellow catfish.The pepsin activity of yellow catfish increased with the increase of feed protein content,on the contrary,the amylase activity decreased with the increase of protein level.The protein content of different feeds had no significant effect on the lipase activity of yellow catfish.With the increase of feed protein content,the average ammonia excretion rate of yellow catfish was also significantly increased.Among them,the average ammonia excretion rate in the 40%and 45%protein content feeding treatments was higher than that of the 25%,30%and 35%protein content feeding treatments.