Effects Of Biochar Mixing On Distribution Characteristics Of Soil Water And Nutrients Under Water/Biogas Slurry Indirect Subsurface Drip Irrigation

In order to explore the influence of biochar addition on soil hydraulic characteristics under indirect subsurface drip irrigation with biogas slurry,four levels of biochar mass percentages(0%,1%,2%,5%)and four levels of biogas slurry content(0,1:8,1:6,1:4)were set in the variable head penetration test,centrifuge test and indoor soil chamber simulation test.The biochar and the biogas slurry use wheat straw and cow dung as raw materials,respectively.The soil saturated water conductivity,soil water holding capacity,soil wetting characteristics and soil nutrient content were investigated.The results are as follows:(1)Under the same soil bulk density,the soil saturated water conductivity decreases firstly and then increases with the increase of biochar content,and reaches the minimum value when the biochar content is 2%,while tends to decrease with the increase of biogas slurry content,the saturated water conductivity decreases with the increase of soil bulk density under different soil bulk density.(2)Under the same soil bulk density,soil water holding capacity increases with the increase of biochar and biogas slurry contents,both biochar addition and biogas slurry irrigation alone can increase soil porosity and capillary porosity,and their coupling effects on soil porosity and capillary porosity are more obvious;under different soil bulk density,soil water holding capacity decreased with increasing soil bulk density;the Van-Genuchten model can accurately fit the soil moisture characteristic curve of each treatment.(3)The shape of soil wetting body is ellipsoid whose long axis flattens in vertical direction gradually.The difference of biogas slurry and biochar content among different treatments had obvious effects on the shape of soil wetting body under indirect subsurface drip irrigation.When the biochar content was 1% or 2%,the migration distance of wetting front and volume of wetting body decrease with the biogas slurry application,in both horizontal and vertical directions,soil water is more conducive to accumulation near plant roots,the range in the wetting body with high water content(greater than soil field water capacity,30.62%)increases,for treatment with 5% biochar content,the horizontal and vertically upward migration distance of wetting front decrease with the application of biogas slurry,while the vertically downward migration distance increase,resulting in an relative smaller area of wetting body with high water content although the volume of wetting body is as big as that of treatment with 2%biochar content;the power function can accurately describe the relationship between the wetting front transportation distance and irrigation time under different treatments.(4)Application of biogas slurry and biochar can significantly increase soil organic matter and total nitrogen content,which is proportional to biogas slurry ratio and biochar mixing amount,the effect of biogas slurry combined with biochar on soil organic matter and total nitrogen content was greater than that of biogas slurry alone.Taking all indexes in consideration comprehensively,the coupling treatment of1:4 biogas slurry ratio and 2% biochar mixture can obtain better soil hydraulic characteristics,which can provide as theoretical basis for the planned field experiment.