Nitrogen-Phosphorus Balance And Aquaculture Water Quality Of Rice-Crayfish Co-Culture

In recent years,rice-crayfish integrated farming has been rapidly developed in the Middle-Lower Yangtze plains.Improving the nutrient management of paddy field is of great significance for regulating the culture environment and improving the utilization rate of fertilizer.Based on previous research,on the one hand,we took field plots as the research object and set different fertilization modes to explore water quality characteristics and N/P balance of rice-crayfish co-culture under different fertilization modes.On the other hand,organic fertilizer was used as the base fertilizer,and different microbial agents were put into it to explore its regulating effect on water quality in the spring and summer breeding season.The results show that:（1）Under the rice-crayfish co-culture,three fertilization treatments were adopt which are organic fertilizer（T1）,controlled-release fertilizer（T2）and humate fertilzere with bacillus bacteria agent（T3）.The rice yield of the three fertilization modes ranged from 6937 kg·hm^-2to 8062 kg·hm^-2,and there was a great difference among different fertilization modes.The treatment with the highest yield was T2.Among the three treatments,the highest yield of crayfish at co-culture stage was T3.In terms of economic benefit,T3 has the best profit,which is 46 098.5 yuan/hm^-2,19.7%higher than T1.The optimal N and P balances were T1 and T3,respectively.Fertilizer application is crucial to the yield of crayfish and rice.Controlled-release fertilizer is a better choice from the perspective of"keeping food in the ground",which can increase farmers’income on the premise of ensuring rice yield.The yield of crayfish can be increased by applying Bacterial culture in crayfish stage and Humic fertilizer in rice stage.（2）Applying appropriate amount of organic-inorganic compound bacterial fertilizer and organic fertilizer during the spring crayfish stage,and the water quality can meet the growth requirements of crayfish;the value of the main water quality indicators during crayfish farming is 0.053～0.22 mg·L^-1for ammonia nitrogen,0.004～0.022 mg·L^-1for nitrite nitrogen,20～35 cm for water transparency,and about7.8for p H;the plankton biomass of the water body is significantly higher than that of the pond without fertilization.Especially,organic-inorganic compound bacterial fertilizer had the best effect in improving aquaculture environment.Under the condition of rice-crayfish co-culture,no basal fertilizer was applied before rice transplanting or direct seeding,and a large amount of fertilizer was spread over the field during the rice turning green and tillering stage,which seriously affected the aquaculture water quality and caused the time lag for crayfish to enter the field activities by 15 days.As mentioned above,Fertilizers must be applied to the soil before rice transplanting or direct seeding to increase the time for crayfish to co-exist with rice in the field.（3）In the rice-crayfish co-culture mode,using organic fertilizer combined with photosynthetic bacteria could effectively improve water quality and reduce the stress response of seedling casting;The concentration of ammonia nitrogen and nitrite nitrogen in water can be significantly reduced in the middle and late stage of the aquaculture.In addition,organic fertilizer combined with photosynthetic bacteria can significantly increase the body length and catch quantity of crayfish.