Interaction between soil moisture and aggregate characteristics under slope land preparation

Soil aggregates can often form the basis of soil structure. This study aims to analyze the relationship between soil aggregates and soil water from the microscopic perspective of soil in the hilly and mountainous slopes. Theoretical support was then provided to further clarify how the soil structure regulated the field water and fertilizer use after land preparation. Two typical measures of land preparation were selected as the horizontal and reverse slope, with the slope farmland as the control. A series of experiments were carried out to explore the interaction between soil aggregates and soil water status. The staining tracer test was also conducted on the plots under different measures of land preparation. Imaging and statistical analysis were finally employed using a scanning electron microscope. The results indicate that the staining was characterized by the movement and distribution of water in the soil, particularly in the same conditions of external water supply. The spatial distribution of soil water was concentrated in the shallow space of the 0-10 cm depth of the soil in the field. A significantly smaller range was observed on the distribution of soil water in the slope farmland field. After horizontal and reverse slope preparation, the degrees of change in the spatial movement of soil water in the field were 11.09% and 7.14% higher than those in the slope land, respectively. Microscopic images of soil aggregates were magnified by 1000 times using scanning electron microscopy. Then the quantitative analysis was conducted using pore analysis software. It was found that the spatial distribution of soil aggregates after horizontal and reverse slope cultivation was more uniform (with average fractal dimensions of 1.16 and 1.18, respectively) than that of the slope-cultivated land (with an average fractal dimension of 1.19). Land preparation reduced the difference in the pore size and composition in the soil aggregates by 5.81% (horizontal) and 10.10% (reverse slope), respectively. The complex behavior was found along the spatial distribution direction of pores in the soil aggregates in the horizontal field (with a probability entropy of 0.957 8). The spatial distribution and movement of soil water were analyzed to couple the coordination degree model. A reference value was obtained to determine the correlation degree of soil water. The coupling coordination degrees of the horizontal platform, reverse slope platform, and slope farmland were 0.62, 0.58, and 0.56, respectively. Gray correlation was employed to analyze the reference value of soil water status and various indexes of aggregates. There was the greatest influence of the spatial distribution in the soil aggregates of the horizontal platform on the spatial distribution and movement of soil water in the field (with a correlation degree of 0.812). However, the size of soil aggregates in the reverse and undisturbed slope cultivated land shared the greatest influence on the spatial distribution and movement of soil water (with correlation degrees of 0.708 and 0.698, respectively). Therefore, the land preparation measures can significantly alter the soil aggregate status of slope farmland, and subsequently affect the soil moisture in the field. Therefore, it is highly required to the optimal measures of land preparation for the sloping farmland in the hilly and mountainous areas. The finding can provide a strong reference to effectively regulate the soil structure and soil water during agricultural production.