Effects Of Biochar On Soil Physicochemical Properties And Rice Growth In Rice Crayfish

Rice-crayfish is a kind of ecological farming mode of compound planting and breeding.This mode realizes"win-win situation of money and grain",promotes agricultural green development,and promotes green transformation of rice production,and has obvious ecological,economic and social benefits.However,in the low lake and waterlogged paddy fields in jianghan Plain,the long-term flooding and high groundwater level caused severe soil hypoxia and accumulation of reducing substances,which led to secondary gley of paddy soil and increased the risk of gley.Biochar is a soil modifier,which is the most widely used measure for soil quality improvement and restoration.Based on this,this paper took the rice-shrimp co-cropping pattern in jianghan Plain and Lake Area as the main research object.Through the paddy field experiment of applying biochar amount in The rice-crayfish of different years,combined with the pot experiment of adding biochar under the simulated rice-shrimp co-cropping water management pattern.The effects of biochar on soil nutrient and soil structure improvement and rice yield increase under The rice-crayfish were studied.The main results are as follows:（1）Biochar significantly increased soil nutrient content in rice-crayfish.In the simulated rice-crayfish water management experiment,the increase of soil nutrient indexes was greater than that in the field experiment.Compared with CK,the total nitrogen content in the simulated rice-crayfish water management increased by 3.4%-66.7%with biochar application.Total phosphorus content increased by 3.2%-17.1%;Ammonium nitrogen content increased by 31.4%-98.5%;Nitrate nitrogen content increased by 6%-39.1%;The content of available phosphorus increased by 16.4%-35.2%;Organic matter content increased by 4.7%-88%;CEC increased by 2.6-9.6%;When p H increased by 0.16-0.31units,the increase rate of biochar treatment was B3>B2>B1.There were no significant differences in ammonium nitrogen content,CEC,nitrate nitrogen content,available phosphorus content and total phosphorus content between B1 and B2 treatments.With the increase of shrimp rearing years,soil nutrient content increased,and the increase of biochar to CR0 nutrient was the largest.（2）Biochar significantly reduced the content of reductive substances in rice-crayfish soil.The reduction of reducing substance content in simulated rice-crayfish water management experiment by biochar was larger than that in field experiment.Compared with CK,the total amount of reducing substance in simulated rice-crayfish and rice-crayfish water management was significantly reduced by 18%-45.3%by biochar application.The content of active reducing substance was reduced by 24.1%-49.1%.The Fe²⁺content was reduced by 8%-33%.The Mn²⁺content was reduced by 17.2%-47.2%.The decrease of biochar treatment was B3>B2>B1,and there was no significant difference in their content between B1 and B2.With the increase of shrimp rearing years,the content of reducing substances increased gradually and reached a significant difference,and the reduction of biochar on CR8 and CR15 was the largest.（3）Biochar improved soil structure and enhanced soil aggregate stability.Compared with CK,biochar application significantly reduced soil bulk density by 7.5%,and the bulk density was negatively correlated with biochar application amount.Soil porosity was significantly increased by 5.9%,and the porosity was positively correlated with biochar application amount.The decrease of biochar treatment was B2>B1,and there was no significant difference in bulk density and porosity between B1 and B2 treatments.Biochar treatment increased the content of large aggregates and decreased the content of small aggregates in soil.Compared with CK,biochar significantly decreased the content of small aggregates with<0.053mm grain size by 10.7%-44.1%.Increased the content of>0.25mm large aggregate by 7.2%-12.5%;The content of 0.25-0.053mm aggregate decreased significantly in CR0 and CR4,by 10.4%-22.3%.It has no significant effect on the content of aggregates>2mm.The average mass diameter（MWD）value was increased by 8%-10.2%.The geometric mean diameter（GMD）value is increased by 6.5%-13.6%.There were significant differences in soil bulk density,porosity and soil aggregate distribution among different years of rice-crayfish,and biochar had the best effect on soil structure of CR8.（4）Biochar promoted the growth of rice-crayfish.The results of water management of simulated rice-crayfish were basically consistent with those of rice-crayfish.Compared with CK,the application of biochar increased the tillering of rice,and significantly increased the plant height of rice by 9.4%-14.9%.SPAD value increased by 16.2%-68.2%;Increased dry matter accumulation by 8.9%-26.1%;The yield increased by 6.3%-17.6%,and the increase rate of biochar treatment was B1>B2>B3.Tiller number,SPAD value,dry matter accumulation and yield showed a trend of increasing first and then decreasing,except that plant height was positively correlated with biochar addition.There was significant difference in rice yield of rice-crayfish,and biochar increased the yield of CR15the most.In conclusion,biochar improved water and fertilizer retention performance of rice-crayfish soil,increased soil nutrient content,improved soil structure,promoted rice growth and increased yield.The application of biochar significantly improved the soil quality of rice-crayfish paddy fields.Considering economic benefits,B1 treatment was more suitable for promotion and application in rice-crayfish paddy fields.