Study Of Rice-Crab Co-Culture System To Assess The Impacts On Production,Soil Fertility And Environment

Rice?Oryza sativa L.?is a staple food for three billion people and paddy fields contribute greatly to greenhouse gases?GHG?emission and environmental nitrogen losses.The co-culture system can increase farm productivity,enhance the utilization of available resources but its role in water and soil quality,and on GHG emissions is not very clear.The aims of the current study are to find the role of rice-crab co-culture?RC?system for?i?improved field productivity,nutrient uptake and farm income?ii?soil nutrient dynamics and their composition in the rice,and?iii?capability to reduce GHG emission and to mitigate the global warming potential.The hypothesis was,the RC system can enhance rice productivity with environmental sustainability resulting and improvement in soil fertility.For this,a field survey was conducted in Panjin city,including two production systems:rice-monoculture?RM?and RC system.Additionally,a field experiment was also conducted with different crab stocking density and feed management including:rice-monoculture?RM?,3000crabs ha^-1 without feed?RC3000?,6000 crabs ha^-1 with feed?RC6000?,and 12000 crabs ha^-11 with 2�feed?RC12000?.Results revealed,that the RC system can improve agricultural production with economic benefits.During field survey higher number of crabs have reduced the number of productive tillers while,the productive traits were improved significantly except 1000-grain weight remained non-significant.Field experiment indicated that suitable stocking density and feed management did not induce a negative effect on any agronomic or productive trait.Grain yield was improved?19.9%?in RC3000,?22.0%?in RC6000,and?14.7%?in RC12000as compared to RM.The improvement of the grain yield was due to the less number of bad quality grains(shrivelled grains spike^-1),and the increase in filled grains spike^-1,seed setting percentage,and 1000-grain weight in the RC system.Grain nitrogen,phosphorus and potassium contents were also improved by RC6000.Farm income and the benefit-cost ratio was higher in co-culture treatment compared to RM,meanwhile,the maximum farm production(16231 yuan ha^-1)and benefit-cost ratio?0.51?were observed in RC6000.Results showed an increase in soil nutrients and improved nutrient accumulation in rice with the RC system.Soil organic carbon,macronutrients?nitrogen,phosphorus,potassium,and magnesium?Mg??,microbial biomass carbon,and nitrogen,micronutrients?copper,zinc?Zn?,and manganese?were significantly improved.From the field survey,results indicated significant improvement in grain TN?9.4%?,calcium?Ca,22.1%?,Mg?7.1%?,and Zn?26.1%?in RC system compared to RM system.In field experiment,the concentrations of Ca,Mg,and Zn were increased as follows:i)Grain Ca in RC3000?23.9%?and RC6000?17.1%?,ii)Mg in RC3000?12.6%?,RC6000?16.3%?,and RC12000?11.8%?,iii)Zn in RC3000?10.8%?,RC6000?5.7%?,and in RC12000?14.8%?.The RC system has also improved nutrients translocation from soil to plant biomass that was the key reason to increase nutrient composition in rice.The study showed that RC system has great capability to improve drainage water quality,reduce GHG emission and to mitigate the global warming potential compared with the RM system.The field survey and experiment both indicated insignificant or relatively low reduction in field water nutrients at different stages of rice crop.This helps to control the water pollution due to excessive nutrients availability in water.Water quality showed was slightly improved in both survey and field study.Ammonia?NH₃?volatilization was reduced significantly with RC3000 and RC6000 treatments but was insignificant with RC12000 treatment during the co-culture period compared to the RM treatment.Total loss was significantly increased in RC12000?9.5%?,but was reduced significantly in RC3000?17.9%?and RC6000?12.6%?as compared to the RM.N₂O emission was reduced significantly in RC3000?74.4%?,in RC6000?71.7%?,and in RC12000?59.2%?.However,CH₄ emission was insignificant in RC3000,but was reduced significantly in RC6000?41.1%?,in RC12000?63.6%?as compared to the RM.Global warming potential?GWI?,was reduced significantly in RC3000?60.4%?,in RC6000?65.5%?,and in RC12000?60.1%?treatments compared with RM treatment.In this thesis,the study concludes the RC system is an innovative approach to increase safe grain production,with reduced nutrients losses,improved soil fertility,GHG emission,and high potential to mitigate the GWI.The crabs stocking density and stocking time play a key role in better system adoption.The study suggests,adopting the co-culture system with optimum stocking density(6000 crabs ha^-1)with optimum feed is a better approach to improve farm productivity,resource utilization,economy,improve soil and plant nutrient status,control N losses,GHG emission and mitigate GWI.The practical application of this system can help to reduce the chemical fertilization dose and to improve the utilization of resources without decreasing rice production.Further research is needed to find the suitable plant�row distance,modify feed quality and quantity,find the suitable combinations of rice and crab verities,demonstrate leaching and runoff losses,and explore the effects of long-term adoption on above said phenomenon.