Role of biochar from corn straw in influencing crack propagation and evaporation in sodic soils

Soil degradation has become one of the serious global environmental problems, biochar is a recyclable natural material which has been widely used in soil remediation. Soil cracking can significantly change the migration path of water and nutrients in the soil, which affects the remediation performance of biochar and plant growth. The effects of different amounts of corn straw biochar on the evaporation and drying shrinkage characteristics of sodic soil are investigated in this paper. Different amounts (by mass) of biochar: 0%, 1%, 2%, 4% and 8% are added to the soil. A customized experimental device is used to measure the rate of evaporation of water and record the images of surface crack development of the samples during drying. Using image processing technology, the crack rate, crack entropy and fractal dimension of the cracks are obtained. The experimental results show that: (1) biochar can change the drying and cracking characteristics of sodic soil by changing the evaporation process of the soil. With biochar contents of 1%, 2%, and 4%, the residual water contents of soil samples are decreased by 4.83%, 43.94% and 85.71%, respectively. With an 8% biochar content, the residual water content of soil sample is increased by 64.49%, (2) the addition of biochar reduces the rate of cracking and fractal dimension of sodic soil. With an 8% biochar content, the rate of cracking and fracture fractal dimension are reduced by 46.39% and 13.74%, respectively, (3) the addition of biochar can effectively reduce the degree of the disorderly arrangement of surface cracks. At biochar contents of 2%, 4% and 8%, the crack entropies are decreased by 2.22%, 6.46% and 7.37%, respectively, and (4) the mechanisms in which biochar changes crack development in sodic soil are: (a) improving the soil texture and reducing the bulk density of soil and (b) increasing the number of water migration channels, soil aggregates and the water retention capacity in the soil.