Effects Of Feeding On Nitrogen Utilization In Rice-Crayfish Co-Culture System

Rice-crayfish co-culture models（RC）is an important form of comprehensive rice farming.It organically combines rice production with crayfish farming.Because of its high economic benefits,it is an important agricultural extension model to improve agricultural output and farmers’income in the middle and lower reaches of the Yangtze River.However,due to farmers’blind pursuit of crayfish production and unreasonable application of foreign material inputs such as feed,the loss of nutrients such as nitrogen and phosphorus increases and the risk of environmental pollution intensifies.Therefore,it is necessary to standardize the feeding management of crayfish and clarify the effects of feeding on the yield of rice and crayfish,the environmental N content of paddy field（water body and soil）,nitrogen utilization rate,and the transformation and flow direction of nitrogen in feed.Based on the RC,two types of experiments were set up respectively:1)field experiment with different feed rates,Four different feed rates were set in the crayfish season:66.7kg/667m²（Feed-3）,,44.5kg/667m²（Feed-2）,22.2kg/667m²（Feed-1）,0kg/667m²（Feed-0）;In the rice season,two fertilization treatments of pure N 6kg/667m²（6N）and0kg/667m²（0N）were set respectively,and all treatments were set for three repetitions.2)Isotopic micro zone test:by feeding ¹⁵N labeled feed,two treatments with different feed rates were set.The total feed rates were 160g/mesocosm（F-1）and 0g/mesocosm（F-0）respectively.All treatments were set for 5 repetitions.Relevant test conclusions are as follows:（1）The study on the effect of feeding on yield showed that feeding could significantly improve rice yield.In the field experiment in 2021,the rice yield of feed-3 was 16.77%higher than that of feed-0 without nitrogen fertilizer;The main reason is the increase of the number of effective panicles in rice.The number of effective panicles in feed-3treatment is 1.30 times that of feed-0.Feeding also significantly increased the yield of crayfish.The yield of crayfish in feed-3 treatment was the highest（89.29 kg/667m²）,which was 61.74%higher than that in feed-0（55.21 kg/667m²）.The micro zone test showed that feeding increased the unit individual size of crayfish and reduced the recapture rate of crayfish.The average individual weight of F-1 crayfish（17.06g）was88.92%higher than that of F-0（9.03g）,while the recapture rate of F-1 was 25.54%lower than that of F-0.（2）Effect of feeding on water body of paddy field:in the crayfish season of RC,the dissolved oxygen（DO）in water body of paddy field is less affected by feeding and significantly affected by temperature.The DO in different periods is as follows:May<April<March.The turbidity of field water（WT）is affected by temperature and feeding.The variation trend of WT with time is:May>April>March.Feeding can significantly reduce WT.In May,WT under feed-3 treatment was 195.33ntu,34.30%lower than Feed-0.In the micro zone test,the contents of NH₄⁺-N,NO₃^--N and TN in paddy water increased significantly due to feeding treatment,and the TN content in water treated with F-1 increased by 65.95%after the test compared with that before the test;TN in field surface water of F-1 increased by 35.50%compared with that of F-0.In the field experiment,the highest values of NH₄⁺-N,NO₃^--N and TN appeared before feeding in March,rather than after feeding,which was mainly caused by the soaking,maturity and decomposition of the previous rice straw.（3）Effect of feeding on paddy soil:in the feeding field experiment,there was no obvious diversity in NH₄⁺-N,NO₃^--N in surface soil between distinct feeding treatments.Along with the lengthen of rice-crayfish time,the content of soil TN in Feed-3,Feed-2 and Feed-1 treatments in October 2021 was significantly higher than that in March 2020,and the content of soil TN after Feed-0 treatment was lower than that before the experiment.In the micro zone experiment,the soil NH₄⁺-N and NO₃^--N of each feeding treatment increased significantly"before planting rice",and F-1 was higher than F-0;Compared with before the experiment,the content of TN increased in F-0 and F-1,and the difference reached a significant level under F-1 treatment.（4）Effect of feeding on Nitrogen Use Efficiency:there was no significant difference in nitrogen content of stem,leaf and panicle of rice under feeding and fertilization treatment,but plant N accumulation was significantly affected;Under 0N treatment,feeding treatment significantly increased the N accumulation of rice,while under 6N treatment,the difference between different feeding treatments was not obvious,and the elevating influence of feeding was masked.The NUE and ANUE of rice were the highest under Feed-0 treatment.Feeding brought exogenous nitrogen,which bring about the cut down of nitrogen absorption and utilization by rice;PNUE and NPEP had no significant difference among feeding treatments,but feeding significantly increased soil SND.Compared with feed-0,feed-3,feed-2 and feed-1 increased by 26.58%,18.12%and16.59%respectively.The field experiment showed that the feed N utilization rate of rice was feed-1>feed-2>feed-3,and the feed N utilization rate was between 31.41%-36.60%,which decreased with the increase of feed consumption.The feed N utilization rate of crayfish was 25.17%-33.73%,and the changes between treatments were feed-1>feed-2>feed-3.With the increase of feed intake,the feed N utilization rate decreased;The results of micro zone test showed that the proportion of feed derived n in crayfish N accumulation was 65.30%.（5）Flow direction of feed nitrogen in RC:Based on ¹⁵N tracer technology,the results of middle universe ecosystem model show that the nitrogen in feed is absorbed and utilized by rice and crayfish,accounting for 8.97%and 23.68%respectively;The residual nitrogen in the soil and water of RC accounted for 4.36%and 9.79%of the total feed nitrogen respectively;The loss of feed nitrogen through drainage and irrigation,ammonia volatilization and other ways accounted for 53.21%.