Effects Of Wheat Straw Biochar On Soil Thermal Properties And Albedo In Sierozem

Biochar is a black granular substance with high carbon content（≥60%）,extremely rich pore structure,large specific surface area and strong adsorption capacity.Lime-lime soil is one of the main soil types distributed in northwest China.It has loose structure,high water permeability,air permeability and low organic matter content.The application of biochar to lime-lime soil is beneficial to improve the properties and structure of lime-lime soil and the productivity of farmland.Soil thermophysical properties are important factors affecting surface energy balance and underlying surface structure in the loess region,affecting various physical and biochemical reactions in the soil,as well as microbial activity and crop growth and development.Different soils have different thermophysical properties and their temperature increases and decreases vary after absorbing certain amount of heat.For the study of wheat straw biochar input of northwest sierozem farmland soil thermal conditions,this study firstly through laboratory test,the wheat straw by biochar quality ratio is 0%,1%,3%,5%of the amount to join sierozem soil,explored the wheat straw to farmland sierozem biochar soil p H,organic matter,bulk density and porosity,and the influence of different biochar and adding amount on the thermal physical properties of soil with different moisture content.Secondly,using field plot test,the fallow period（10/12/2019-12/18/2019）applying to set different content of wheat straw biochar:contrast 0 kg·m^-2（BC0）,1 kg·m^-2（BC1）,4 kg·m^-2（BC4）,in situ determination of each plot soil moisture content,albedo,the heat capacity,thermal conductivity,thermal diffusivity and temperature index,explore the wheat straw biochar input of fallow period farmland soil thermal physical properties and albedo,and the soil thermal physical properties and albedo and the response of the soil temperature,respectively.Finally,in the growing period（6/7/2020-8/18/2021）using field plot test,the gradient in fallow period of treatment,on the basis of each treatment,respectively,set up two vice:wheat（BC0+,BC1+,BC4+）and wheat（BC0,BC1,BC4）,the comparison and analysis with&without wheat growth conditions,biochar for growing period sierozem farmland soil albedo and the effect of thermal physical properties and mechanism,and albedo and thermal physical properties and soil temperature response.The main research results are as follows:（1）With the increase of wheat straw biochar addition,the bulk density of lime lime soil decreased gradually,while the soil porosity,p H value and organic matter content increased gradually.Under the same water content,biochar significantly reduced soil heat capacity,thermal conductivity and thermal diffusivity.When the addition amount of biochar was the same,the thermal conductivity and volumetric heat capacity of soil increased with the increase of water content,and the volumetric heat capacity and water content had a positive linear correlation,and the thermal conductivity and water content had a logarithmic relationship.The thermal diffusivity increased first and then decreased with the increase of water content.（2）During the fallow period,compared with BC0,the maximum reduction of soil thermal conductivity under BC1 and BC4 treatment was 24%and 25%,respectively.Compared with BC0,the maximum reduction of soil thermal diffusivity under BC1 and BC4treatment was 14%and 25%respectively.For heat capacity,under the condition of no precipitation and no freezing,the decrease of BC1 was greater than that of BC4.Compared with BC0,the maximum decrease of BC1 and BC4 heat capacity was 33%and 17%respectively.In addition,the soil moisture content decreased with the increase of biochar content in the fallow period without precipitation,but increased with the increase of biochar content in the freezing-thawing period at low temperature,and all thermal parameters were basically consistent with the change trend of moisture content.The soil thermal condition was reflected by the temperature.The 5 cm section of soil was greatly affected by near-surface air temperature,and the temperature change pattern was not obvious.The soil temperature in the20 cm section was less affected by the near-surface air temperature and decreases with the increase of biochar applied.The average temperature of BC1 and BC4 is 0.8%and 1%lower than that of BC0.In fallow period,the surface albedo decreased with the increase of the amount of biochar applied,and decreased significantly with precipitation and evaporation,but there was no significant negative correlation between the albedo and water content and temperature.The results showed that biochar affected the change of soil thermal properties in farmland mainly by affecting water content.The addition of wheat straw biochar could affect soil temperature in farmland by affecting soil thermal properties.（3）During the planting period,the maximum decrease of water content of BC1 and BC4versus BC0 was:19.60%and 25.75%respectively,the maximum decrease of thermal conductivity was:28.18%and 50.80%respectively,and the maximum decrease of thermal diffusion rate was:37.41%and 44.36%respectively,the maximum increase rate of 5 cm temperature is:28.22%and 34.65%respectively,and the maximum increase rate of 20 cm temperature is:32.44%and 37.11%respectively.The maximum increase of water content of BC1 and BC4 versus BC0 was 36.71%and 33.86%respectively,the maximum decrease of thermal conductivity was 8.91%and 16.64%respectively,the maximum decrease of thermal diffusion rate was:6.43%,20.51%respectively,and the maximum decrease of 20 cm temperature was 4.45%and 3.14%respectively.Whether or not wheat growth,increased soil thermal capacity when biocarbon is added to 1 kg m^-2,and reduced soil thermal capacity when added to 4 kg m^-2.Under bare soil condition,albedo decreased with the increase of biochar application amount,and there was no obvious rule between albedo change and water content change of each treatment.Wheat growth could reduce the surface albedo,and cover up the influence of water content and biochar on the surface albedo.With the growth of wheat,the differences of albedo among different treatments gradually reduced.The effect of biochar on soil thermal properties and temperature was related to the application amount of biochar.Under the condition of wheat growth,the effects of biochar on soil thermal properties and temperature are not only affected by the application amount of biochar,but also inhibited by the growth of wheat.Meanwhile,wheat growth can also affect soil thermal properties and temperature,and the degree of influence is inhibited by biochar.