| Soil structural stability is an important index to evaluate soil fertility and quality.The rheological parameters obtained by rheological method can reflect the number and intensity between soil particles contact,and thus describe the stability of soil microstructure.Biochar is often used as soil improvement material,which can effectively increase soil carbon sequestration,structural stability and water infiltration.Therefore,the rheological method can provide more abundant evaluation parameters for the effects of biochar on soil microstructure stability.In this study,spent mushroom substrates,spent oyster mushrooms substrates and spent agaric substrates were used as raw materials to prepare biochar at different pyrolysis temperatures.X-ray diffraction（XRD）and organic element analysis were used to characterize the properties of biochar,so as to explore the optimal pyrolysis temperature for preparing biochar.Secondly,the effects of mushroom substrates biochar and soil matric potentials on the microstructure stability of Lou soil and Loessal soil were studied.Finally,the mechanism of biochar on soil microstructure stability after short-term culture experiments was discussed.The results can provide some scientific basis for soil structure improvement on Loess region.The main results of this study are as follows:（1）The effects of different pyrolysis conditions on the properties of spent mushroom substrates biochar were investigated.Three raw materials of mushroom substrates,oyster mushroom substrates and agaric substrates,were used.Spent mushroom substrates biochar（MSB300/500/700）,spent oyster mushroom substrates biochar（OSB300/500/700）and spent agaric substrates biochar（ASB300/500/700）were prepared at 300,500 and 700℃to determine their properties.The results showed that with the increase of pyrolysis temperature,the yield of the three kinds of biochar decreased,the pH,specific surface area and ash content increased.Also,a good pore structure was formed in the biochar,the number of surface functional groups,the thermal stability,and the absolute value of zeta potential of biochar all increased with the increasing pyrolysis temperature.The biochar prepared at 500℃had the best properties,and the yield and ash content of spent mushroom biochar were the highest.Spent Oyster mushroom biochar had larger specific surface area and good thermal stability,while fungus bran biochar contained more mineral components and good pore structure.（2）The effects of biochar and matric potentials on soil microstructure stability were quantitatively evaluated.The rheological method was used to investigate the stability of soil microstructure under different biochar materials（MSB500,OSB500,ASB500）,the different amounts（0,1,3,5,7%）and matric potentials（0,-3,-6,-10 KPa）by amplitude scanning experiment.It was found that G’LVE,τmax,τLVE,τYP and G’YP of the two soils increased with the increase of biochar content,andγLVE did not change significantly.The deforation resistance and microstructure stability of the soils increased,while Iz andγYP decreased,indicating that the soil rigidity increased.With the decrease of matric potentials,G’LVE,τmax,τLVE,τYP and G’YP increased first and then decreased on the whole.The stability of soil microstructure was stronger at-3 KPa and-6 KPa than that of-10 KPa,indicating that soil cohesion increased during the drainage process.At 0 KPa,Iz andγYP reached the maximum value,and the soil particles were arranged in the best way.（3）The effects of biochar on soil microstructure stability under short-term culture conditions were studied.The amplitude scanning experiment in the rheological method was used to explore the changes of the microstructure stability of Lou soil and Loessal soil after10 months of greenhouse culture under different biochar（MSB500,OSB500,ASB500）and different addition amounts（0,1,3,5,7%）.With the increase of biochar addtion,pH,calcium carbonate,CEC,organic matter and free iron oxide contents of Lou soil and Loessal soil both increased;G’LVE,τmax,τLVE,τYP and G’YP firstly increased and then decreased,while Iz,γLVEandγYP decreased.The results showed that with the bonding of biochar-soil particles and organic-soil mineral complexes,the cohesion of soil increased,and the shear and deformation resistance of soil increased.However,the deformation range decreased.When the application of baichar were>1%,the coarse particles of biochar were filled into the soil pores,resulting in strong friction,leading to the increase of soil brittleness.Comparing the two soils,the microstructure stability of Lou soil was greater than that of Loessal soil. |
