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Alkaline clayey soil is considered to be a degraded soil, which causes serious issues in engineering and construction projects. The formation and development of desiccation cracks in alkaline clayey soils is a complex process affecting the strength, stability, and permeability of these soils. Therefore, to investigate how soda content can inhibit the development of desiccation cracks in alkaline clayey soils in Ulanhot, Inner Mongolia, China, free desiccation tests were performed to examine the cracks in alkaline clayey soil samples with different soda (Na2CO3) contents in the laboratory. During the cracking process, the changes in water content and the occurrence and evolution of cracks were recorded with a camera. Digital image processing was performed to analyze the structure characteristics of the surface cracks. The results indicated that the characteristics are influenced by the different soda contents. The soda inhibited the development of desiccation cracks in alkaline clayey soils. Three stages were found in the process of desiccation cracking in accordance with the rate of water loss: the residual, normal, and structural shrinkage stages. At <0.4 mol L-1 Na2CO3, the "three straight lines" model could be used to describe the volume shrinkage. However, at >0.4 mol L-1 Na2CO3, the structural shrinkage stage disappeared. Moreover, based on the general soil volume change equation and fractal theory, a model was formulated to quantitatively explain the relationship between the fractal dimension and the volume changes in the soil. The experimental results and equations are important for reducing subgrade deformation and slumps.

The fate of pig (Sus scrofa) slurry labeled with 15N was investigated when applied on a clay soil (fine, mixed, frigid, Typic Humaquept) and a sandy loam (loamy, mixed, frigid, Typic Dystrochrept) cropped to maize (Zea mays L.) in 2000 and to barley (Hordeum vulgare L.) in 2001. The slurry was applied in spring 2000, and plant and soil samples were collected at 6 h (Day 1) and at Days 14, 42, 96, and 413 after application. The samples were analyzed for 15N content in plant, in whole soil, and in soil NH4+-N, NO3--N, organic N, and clayfixed N pools. Percentage 15N recovery was >93% in both soils at Day 1 and decreased slowly thereafter. Rapid clay fixation of slurry 15 occurred at Day 1, and was greater in the clay soil (34% of applied 15N) than in the sandy loam (11%). At Day 96, less of the applied slurry 15N was recovered in maize grown on the clay soil (29%), as compared with the sandy loam (50%). At the same period, the residual soil 15N was mostly present as organic N and NO3-N in the sandy loam, and as organic and clay-fixed N in the clay soil. At Day 413, 15N recovery in barley was about 3% of the initially applied N in both soils. The 15N recovery was generally higher in the clay soil than in the sandy loam, but total 15N recovery from the soil-plant system was similar for both soils. We conclude that soil type had little influence on the total 15 recovery from the soil-plant system, but significantly influenced the fate of slurry N in the various soil pools and plant N uptake on the year of application. [ABSTRACT FROM AUTHOR]