Effects of freeze-thaw cycles and zeolite blending on black soil physical properties

The freeze-thaw cycle is one of the causes of soil erosion in the black soil region of Northeast China. The application of soil conditioner is an effective way to reduce soil erosion. Natural zeolite is an environmentally friendly material and soil conditioner with a wide range of sources, low prices, non-toxic or harm. In this study, the black soil of the Songliao Plain of Northeast China was taken as the research object. Random sampling was carried out at multiple sites in the experimental farmland. Soil moisture content was determined by drying method. The samples of black soil were dried after debris removal. According to the percentage of aggregates of different grain sizes, the soil was reconstructed after sieving. The natural zeolite and the black soil were thoroughly stirred and mixed according to the mass ratio of 0, 5%, 10%, 15%, 20%, then the mixed soil samples were used for pot experiment and soil column. The potted soil and soil column were placed in a temperature-adjustable freezer to simulate the freeze-thaw cycle. The initial soil water content of potted soil and soil column was 22.5%, which was consistent with the soil water content of cultivated land when soil was sampled. In this study, freeze-thaw cycles were controlled for 0, 1, 3, 5 and 7 times, and the same proportion of zeolite mixed with black soil was repeated twice under the same freeze-thaw cycles. The effects of freeze-thaw cycles and zeolite blending on black soil physical indices were studied by comparing the black soil without freeze-thaw cycles or without zeolite blending. Soil physical indexes include soil bulk density, soil total porosity, soil pore distribution, and soil cohesion force and soil internal friction angle. Soil bulk density was measured by ring knife method, soil total porosity was calculated by empirical formula, and soil pore distribution was measured by vacuum freeze-drying and mercury intrusion meter method. Soil cohesion force and soil internal friction angle were determined by triaxial shear test. All indicators were averaged by two repetitions. The research shows that: 1) For the black soil without zeolite addition, freeze-thaw cycles increase soil bulk density, soil cohesion force, micropore and sub-macropore, decrease soil total porosity, soil internal friction angle, mesopore, macropore and average pore diameter. Zeolite blending can reduce the effect of freeze-thaw cycles on soil physical indexes except soil internal friction angle. The larger proportion of zeolite, the more obvious effect of reducing the effect of freeze-thaw cycles. 2) For the black soil that has not experienced freeze-thaw cycles, soil bulk density, soil cohesion force, soil internal friction angle, soil micropores increase, soil total porosity, mesopores and average the pore diameter decreases after zeolite blending. The effect of freeze-thaw cycles on the effect of zeolite-modified black soil will have a negative impact. However, as the zeolite blending ratio increases, the effect of freeze-thaw cycles weakens. This study can lay a foundation for the follow-up study of soil freeze-thaw cycle, and also provide a reference for soil improvement in the black soil region of Northeast China. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.