| Biochar is a black particulate matter obtained by high temperature pyrolysis of biomass such as straw and sawdust under anoxic environment.It has the characteristics of high carbon content,rich pore structure and functional groups,and high specific surface area.As lime lime soil is widely distributed in Northwest China,the application of biochar to lime lime soil can effectively alleviate the characteristics of limestone soil looseness,barrenness,poor agglomeration and poor organic matter content.Soil thermophysical properties mainly include heat capacity,thermal conductivity and thermal diffusivity,which are key factors affecting the internal heat balance of the soil,and are closely related to the radiant energy absorbed by the surface.The albedo is the main parameter reflecting the radiant energy absorbed by the surface soil.Soil temperature affects soil microbial activity,nutrient supply,water and air movement and many other physical and biochemical processes.Studying the changing laws of thermophysical properties is of great significance for regulating soil temperature and improving soil fertility.In this study,corn stalk biochar was selected,and limestone soil was used as the test soil.The test is divided into two parts.On the one hand,the physical and chemical properties of the soil and the change law of thermophysical properties such as heat capacity,thermal conductivity and thermal diffusivity under different application rates of biochar are measured through laboratory test conditions and the mechanism is explored;on the other hand,through a period of time A one-year field trial to explore the changes in the field surface albedo in different periods,analyze the changes of surface soil temperature(0～2.5cm)and deep soil temperature(5～10cm),and use heat pulse technology to dynamically monitor Changes in thermal properties such as soil heat capacity,thermal conductivity,and thermal diffusivity under different weather and seasons.The correlation between biochar,soil bulk density,and water content and its influence on soil thermal properties are analyzed.The main research conclusions are as follows :(1)Under laboratory tests show that the application of biochar has a significant effect on the physical and chemical properties of limestone soil.Biochar can increase the p H of the soil.At the same time,with the increase of the amount of biochar,the organic matter content in the soil increases significantly.The organic matter content of BC100,BC300,and BC500 increase by 14.6%,40.9%,and 52.8%,respectively.Biochar can reduce soil bulk density,and the decrease rates of BC100,BC300,and BC500 are 11.65%,24.27% and 35.92%,respectively.Biochar can enrich the pore structure of the soil,and the amount of biochar is positively correlated with the total porosity.The soil water holding capacity is closely related to the pore structure.The change of the pore structure makes the soil water permeability and air permeability stronger,and the water retention capacity of the soil is stronger.The water holding capacity of the soil with different amounts of carbon is BC500>BC300>BC100.The fertility of lime lime soil is poor,and the cation exchange capacity of biochar is significantly increased after the addition of biochar,but the contribution to the effective phosphorus content is minimal.Different application rates of biochar have different effects on soil thermophysical properties.In general,biochar can reduce the heat capacity,thermal conductivity and thermal diffusivity of limestone soil,and the greater the amount of carbon applied,the greater the decrease.Under the conditions of a certain bulk density and water content,biochar changes the composition of the solid phase of the soil,which is the main reason for the decrease in heat capacity.Biochar treatment significantly reduces the soil thermal conductivity.The soil thermal conductivity increases linearly with the increase of water content.The main reason is that water infiltration causes the formation of a water film between the biochar and the soil particles.The formation of the water film makes the soil particles and the biochar The increase in the contact area between the two makes the thermal conductivity change significantly.The soil thermal diffusivity increases first and then decreases with the water content.The low thermal diffusivity of biochar itself and the soil insulation effect caused by the larger porosity are the main reasons for the decrease of thermal diffusivity.(2)Field experiments in the fallow period show that biochar can change the heat absorption performance of the soil,reduce the surface albedo,and have an impact on the thermophysical properties such as soil heat capacity,thermal conductivity,and thermal diffusivity.Compared with the control,the surface albedo of 1.0 kg·(m2·a)-1(BC10)and 4.0kg·(m2·a)-1(BC40)treatments with biochar applied amount decreased by 11.7% and 23.5%,respectively.Changes in soil water content will affect the surface albedo,and when the soil water content changes significantly,biochar is no longer the main factor affecting the surface albedo.Biochar has a significant effect on the surface soil temperature of 0-2.5 cm,but it has no significant effect on the depth of 5-10 cm.The reason is that the soil temperature is affected by both the surface albedo and the soil thermal conductivity.Biochar reduces the soil thermal conductivity.It limits the transfer of soil heat from the surface to the deep layer,resulting in insignificant temperature changes in the deep layer.Biochar significantly reduced the soil water content.Compared with the control,the soil water content of BC10 and BC40 treatments decreased by 11.8% and 11.4% respectively,which was mainly related to the soil type and its basic physical and chemical properties.Under field conditions,the application of biochar significantly reduced the soil bulk density,and the soil heat capacity,thermal conductivity,and thermal diffusivity decreased significantly with the increase in the amount of carbon applied.Correlation analysis showed that the biochar treatment,moisture content,and bulk density were the same as the thermophysical parameters Significant correlation,of which the impact of changes in water content is the most significant.(3)Field experiments during the planting period showed that during the corn planting period,the effect of biochar on the surface albedo was different at different stages of corn growth.With the growth of the corn crown structure,the weakening effect of biochar on the surface albedo gradually decreased or even disappeared.It can be seen that the impact of biochar on the surface albedo is related to the type of crop coverage.The effect of biochar on soil water content is different from that of the fallow period.The soil water content of the BC40treatment is significantly higher than that of the control.The reason for this result is related to the basic physical properties of limestone soil,and it can also indicate the biological properties to a certain extent.The longer the time charcoal is added to the soil,the more stable the soil is,and the more it can improve the water holding capacity of the soil.The application of biochar significantly reduced the soil bulk density,and the heat capacity,thermal conductivity and thermal diffusivity decreased significantly with the increase in the amount of carbon applied.In the absence of water infiltration,biochar mainly reduces the soil bulk density through its own structural properties,and did not follow the observation date.The changes show large fluctuations and basically stabilized,but the growth of corn will affect the effect of biochar on the thermophysical properties of the soil.In summary,the thermal properties and surface structure of biochar can directly reduce soil thermal conductivity and thermal diffusivity.It can also indirectly reduce soil thermal properties by reducing soil bulk density and affecting soil water content,thereby affecting soil energy balance. |
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