The Physical Obstacle Factors Of Shajiang Black Soils And Its Improvement

The Shajiang black soils (Vertisol) are expansive clayey soils with a swelling-shrinkage properties. Because their high expansive clay results in high potential for shrinkage-swelling and stickiness, the soils have high swelling pressure, poor soil structure, and deep cracks when dry as well as sticky nature when wet. These factors lead to significant restriction to crop growth and difficulties in their management. Therefore, these soils represent the typical low-yield soil type in Northern China. This study deals with the swelling-shrinkage, tensile strength properties of Shajiang black soils distributed in Northern China to characterize their physical properties. The second objectives is to determine the effect of soil amendments on selected soil physical properties in the Shajiang black soil, thereby evaluating the possible benefits of soil amendments in the low-yield soils. The obtained results are as follows:1. The pH values of the samples varied within the range of6.0-8.0. The soil pH value of A layer is lower than those of B horizon. The soil organic matter (SOC) content decreased with a increase of soil depth. Soil cation exchangeable capacity (CEC) is significantly related with soil clay content (y=83.25x+10.67, R2=0.542), indicating that clay is the controlling factors of CEC in the soils.2. The coefficient of linear expansion (COLE) of Shajiang black soils ranged from4.09%-13.73%with the mean value of9.94for A layer and9.84%for B layer, which indicated the swelling-shrinkage characteristics of Shajiang black soils. The soil COLE was found to be significantly related to the clay content.3. The influence of soil amendments on the physical quality of Shajiang black soils was evaluated by the tensile strength, Atterberg limits, and COLE. The Shajiang black soil was amended with biochar (straw biochar, woodchips biochar, rice husk biochar, and wastewater sludge biochar) and coal fly ash at the rate of0,20,40, and60g·kg-1soil. The application of amendments significantly increased soil pH, available P and K, and soil base ion content. The application of rice husk biochar and woodchips can increase soil plastic limit, however, addition of straw biochar and wastewater sludge biochar decrease the soil plastic limit. The application of five soil amendments can reduce the soil COLE. The woodchips biochar and waste watersludge biochar can significantly (p<0.05) reduce soil COLE. The coal fly ash can reduce the compressive strength, while the amount of coal fly ash has no significant effect on the soil strength. The applicationof biochars significantly reduce the compressive strength. The straw biochar and woodchips biochar have larger impact on the compressive strength than the waste water sludge biochar.