The rice-crayfish co-culture system is a comprehensive planting and breeding mode combining rice planting with crayfish breeding.Compared with rice monoculture,rice-crayfish co-culture system can improve the utilization rate of rice resources,affect the physical and chemical properties of soil,and the carbon and nitrogen mineralization characteristics and greenhouse gas emission characteristics of soil itself may also change with the extension of co-culture years.Therefore,this study intends to compare the soil(8y,15y)of different rice-crayfish co-culture years with that of rice monoculture,Using the indoor biological culture method,the characteristics of soil carbon and nitrogen mineralization and greenhouse gas emission in rice and shrimp fields with different co-culture years were studied,and the dynamic model of soil carbon and nitrogen mineralization was fitted in order to provide data support for the theoretical research of long-term rice-crayfish co-culture system and reference for field fertilization measures.The conclusions of this study are as follows:1.Compared with rice-crayfish co-culture system,rice monoculture can significantly increase the contents of soil total nitrogen,organic carbon,available phosphorus,available potassium,nitrate nitrogen and ammonium nitrogen.With the extension of co-culture years,the contents of soil total nitrogen,organic carbon,nitrate nitrogen and ammonium nitrogen will increase significantly.The mineralization rate of soil organic carbon in different culture periods showed that rice-crayfish co-culture system was higher than rice monoculture,and increased with the extension of co-culture years.The mineralization rate of soil organic carbon showed a trend of rapid and violent at first,and then slow and stable with the culture time.Soil organic carbon mineralization mainly occurred in the first 7 days of culture.The mineralization rate in different periods increased first and then decreased with the increase of water content(60%water content>90%water content>30%water content).2.The cumulative mineralization of soil organic carbon showed that rice shrimp cocropping was significantly higher than rice monoculture,and increased with the extension of co-culture years.Under different water content,60%water content was significantly higher than 90%water content.As a whole,it increased first and then decreased with the increase of water content(60%water content>90%water content>30%water content).Soil potential mineralizable organic carbon showed that rice-crayfish co-culture system was significantly higher than rice monoculture,and increased with the extension of co-culture years.In the case of different water content,it shows the trend of first increasing and then decreasing with the increase of water content(60%water content>90%water content>30%water content).Under the conditions of low water content and high water content(30%and 90%water content),the extension of co-culture years showed significant differences in soil potentially mineralizable organic carbon.Under the condition of medium water content(60%water content),the mineralization rate constant of soil organic carbon in rice-crayfish co-culture system was significantly higher than that in rice monoculture,and increased significantly with the extension of co-culture years.Under different water content,the medium water content(60%water content)was significantly higher than that in low water content and high water content(30%and 90%water content).The half cycle variation of soil organic carbon is opposite to the mineralization rate constant of soil organic carbon.3.The accumulation of nitrate nitrogen and ammonium was mainly concentrated before 7 days of culture.The soil net ammoniation rate showed that the rice-crayfish co-culture system was significantly higher than the rice monoculture,and increased significantly with the extension of co-culture years.Under different water content,it showed a trend of first increasing and then decreasing with the increase of water content(60%water content>90%water content>30%water content).During the whole culture period,the contribution rate of soil net ammoniation rate to soil net mineralization rate was more than 90%.The amount of soil potentially mineralizable organic nitrogen showed that the rice-crayfish co-culture system was significantly higher than the rice monoculture,and increased significantly with the extension of the co-culture years.With the increase of water content,it first increased significantly and then decreased significantly(60%water content>90%water content>30%water content).Under the condition of high water content(90%water content),the rate constant of soil organic nitrogen mineralization showed that the rice-crayfish co-culture system was significantly higher than the rice monoculture,and increased significantly with the extension of the co-culture years.4.Soil CH4emission shows a negative emission or zero emission trend.N2O emission is concentrated in the first five days of culture.The cumulative emission of CH4is negative,which is reflected in the absorption of CH4.The cumulative emission of N2O is significantly higher in rice-crayfish co-culture system than in rice monoculture,and increases significantly with the extension of co-culture years,The influence of different water content on N2O cumulative emission shows a trend of first increasing and then decreasing with the increase of water content(60%water content>90%water content>30%water content).The change trend of soil organic carbon mineralization is consistent with that of soil organic carbon mineralization.The global warming potential of soil showed that rice-crayfish co-culture system was significantly higher than rice monoculture,and increased significantly with the extension of co-culture years.With the increase of water content,it first increased significantly and then decreased(60%water content>90%water content>30%water content).In conclusion,long-term rice-crayfish co-culture system can significantly improve soil fertility and is conducive to soil carbon and nitrogen mineralization,but it will significantly increase the global warming potential.It is most suitable for soil carbon and nitrogen mineralization under the condition of 60%water content,and it will also increase the global warming potential.Therefore,in the actual field operation,the application of fertilizer can be reduced to a certain extent for the long-term rice-crayfish co-culture system soil. |