The Effects Of Crayfish Feeding And Straw Returning On Nitrogen Recycling And Utilization In Rice-crayfish Farming Ecosystem

There are many issue about resources utility in current productivity of paddy field in China,such as great costs of agricultural input and lower productivity.How to rationally use resources in rice field improving the efficiency of rice production is one of major major challenges to facing rice production in China,especially in the middle and lower reaches of Yangtze River.The rice-crayfish co-production mode is a high-efficiency and advanced cultivation method in rice field.The combination of rice planting and crayfish culture can make full use resources of light,temperature,water and soil to improve the comprehensive benefits of rice fields.In order to clarify the effects of rice straw returning,feeding,fertilization and other factors on rice yield,soil properties and nitrogen use efficiency.Three experiments were conducted,i.e.,(1)Straw returning field feeding experiment,including 6 treatment,i.e.,straw returning and feeding(SF),straw returning and no feeding(SNF),no straw returning and feeding(NSF),no straw returning and no feeding(NSNF),rice single crop straw returning(CKS),and rice single crop no straw returning(CKNS).(2)Isotope tracer experiment,twelve micro-regions was established in each plot of SNF,SF,NSN,NSF and CKS treatments,simultaneously,twelve micro-regions in each plot were divided into three groups to set three nitrogen supply with four repetitions,i.e.,0 kg/hm~2,75 kg/hm~2,150 kg/hm~2,225 kg/hm~2;(3)Comparative experiment on supply years of nitrogen fertilizer in rice and crayfish system;a split plot design with three replications was used,supply years of nitrogen fertilizer in rice and crayfish system were assigned to the main plots,e.g.,2 years,5years 8 years and rice mono-cropping(CK).Subplots were assigned to supply rate of nitrogen,i.e.,0 kg/hm~2,75 kg/hm~2,150 kg/hm~2 and 225 kg/hm~2.the main results are as follows:(1)The effects of treatments on yield:Feeding and fertilization cause significant different in rice yield.The rice yield in SF treatment had the highest rice yield,reaching to 9.51 t/hm~2,yielding by 8.7%compared with SNF treatment,SF and NSF in crayfish yield were significantly greater by 52%and 50%than SNF and NSNF respectively.The grain yield in moderate nitrogen application was significantly higher than that in no nitrogen application and excessive nitrogen application.The main factors affecting grain yield were affected by panicle number and number of spikelets per panicle;(2)The effect of treatments on soil properties:The ammonium content of SF treatment in the tillering stage was 30.53 mg/kg,which increase to 23.8%higher than that per-sowing stage.The content of ammonium nitrogen in the soil increased significantly compared with the term of consecutive rice-crayfish co-culture,while the content of nitrate nitrogen decreased significantly with the year of co-culture.With the extending years of the co-culture,the total nitrogen in the soil showed an increasing trend.The total nitrogen and ammonium nitrogen in 9 consecutive rice-cryfish co-clture was 39.0%and 59.4%higher than that in the rice field with no feeding,and nitrate nitrogen decreased 182.8%.(3)The effects of treatments on nitrogen use efficiency of rice plant:two treatments with the highest nitrogen accumulation were SF and SNF had the greatest nitrogen accumulation in rice plant,which was respectively 115.02 kg/hm~2 and126.35 kg/hm~2;while Nitrogen use efficiency reduced with following order,SF>SNF>NSF>NSNF>CKS>CKNS,and SF treatment reached to 56.90 kg/kg,feeding treatment can increase the nitrogen accumulation in rice plants,and significantly improve Nitrogen use efficiency of rice plant;within the same years of rice and crayfish co-culture,Nitrogen use efficiency and Nitrogen uptake efficiency of rice plant were reduction with raising nitrogen fertilizer,;with the extending years of rice-crayfish co-colture,the Nitrogen utilization efficiency of rice plant was decreased,but Nitrogen harvest index was increased,which inhibited nitrogen transfer toward grain raising nitrogen surplus in the soil,which resulted in a large amount of nitrogen waste.With the prolong years of the rice-cryfish co-culture,Nitrogen use efficiency,Nitrogen utilization efficiency and Nitrogen harvest index of rice plant were improved,which is more conducive to the nitrogen uptake of rice plant supporting the transformation of nitrogen toward the grains of rice.Therefore,with the appropriate nitrogen application,the nitrogen uptake efficiency of rice decreased with the increasing years of rice-crayfish co-culture,but it was helpful for nitrogen accumulation of rice grain.(4)The balance and compensation of nitrogen in the cooperative mode of rice and crayfish:The absorption of nitrogen in the fertilizer is lowering by rice plant,ranging from 7.08%-16.60%;with the increase of nitrogen fertilizer application,the proportion of nitrogen recovery and utilization in fertilizer is significantly reduced,and the massive loss of nitrogen is obviously increased.Both straw returning and feeding treatment could compensate the effect of a part of the nitrogen fertilizer,and the compensation ability to nitrogen in the feeding treatment is more obvious.The accumulative rate of nitrogen in rice grain of the NSNF treatment was 6.81%and3.28%higher compared to NSF and SNF treatment respectively.With the increasing years of the co-culture,The higher nitrogen application raised nitrogen surplusand accumulation in the soil,and obviously stimulating the nitrogen compensation.Therefore,the rate of nitrogen application could be decreased with the increasing years of rice-cryfish co-culture.