Effects Of Biochar On The Thermal Conductivity Of Soil And Its Mechanism

Soil thermal conductivity is one of the important soil thermal parameters and plays an important role in the transmission of soil heat on the underlying surface.Soil thermal conductivity is closely related to soil bulk density and soil moisture content.Biochar can reduce soil bulk density and increase soil moisture content.Therefore,in this study,soil bulk density,water content,and thermal conductivity are the main research indicators to explore the effects on soil thermal conductivity effects and mechanisms of biochar.The experient consists of two parts.One is the indoor soil column simulation experiment,including soil loss simulation and soil compaction simulation.The two simulation experiments are based on black soil,brown soil and sandy soil as the test soil,both set 4 field treatments:B0?control,No biochar?,B1(1%carbon,w w^-1,the same below),B3?3%biochar?,and B5?5%biochar?;One is the 6-year Field location monitoring test and field plot test.The test soils are all black soil.The CK?control,no biochar?,B2.25(2.25 t hm^-2 a^-1 biochar)and B4.5(4.5 t hm^-2 a^-1biochar)are set in the positioning test.The experimental treatment settings in the field plot are the same as those in the simulation experiment.The main conclusions of this study are as follows:?1?The application of biochar has a significant effect on the soil thermal conductivity of the field,and the soil bulk density and volume water content have a significant correlation with soil thermal conductivity.The application of biochar can improve the average temperature of 0-7.5 cm surface of bare soil and the highest temperature on the surface,and the maximum temperature decreases with the increase of carbon content,and the biochar has no obvious effect on the temperature of 10-12.5 cm soil layer.?2?The soil thermal conductivity increased with the increase of volume water content in logarithmic form.The application of biochar has no effect on the increase of thermal conductivity with the increase of volume water content,but increases the growth rate of the thermal conductivity of black soil and brown soil,and reduces the growth rate of the thermal conductivity of sand soil.?3?Application of biochar can reduce soil thermal conductivity,mainly because biochar reduces soil bulk density and overall thermal conductivity of soil particles.Filtration experiments show that biochar decreased soil bulk density,improve the quality of soil water content,but had no significant effect on soil volumetric water content,make three kinds of soil)(black soil,brown soil and sandy soil thermal conductivity decreased with increasing carbon content.The compaction experiments show that the thermal conductivity of the three soils decreases with the increase of carbon content,and the thermal conductivity increases with the increase of bulk density.Therefore,the application of biochar leads to the decrease of soil thermal conductivity.First,biochar increases the volume ratio of gas phase in the soil by reducing the volume ratio of solid phase particles in the soil.Second,the addition of biochar changes the composition of soil solid phase materials and reduces the thermal conductivity of soil solid phase materials.?4?After 6 years of continuous application of biochar,the physical and chemical properties of black soil have been improved,and biochar has the potential to alleviate the degradation of black soil in northeast China.