Background and Objectives:
Infiltration is one of the most important hydraulic properties of soil, representing the entry of water into the soil, usually occurring in a vertical direction (Faki et al., 2018). This soil property plays a crucial role in the natural water cycle (Turner, 2006) and has significant implications for soil management (Turner, 2006). In semi-arid regions, this hydraulic property is particularly important not only for meeting the water requirements of rangeland and rainfed crops but also for reducing runoff as well as soil erosion (Vaezi, 2018). Several factors influence soil infiltration, which can be generally categorized into three groups: (1) spatial and surface characteristics, (2) soil properties, and (3) climatic and environmental conditions (Zoaid, 2021; Vaezi, 2018). This study focused on soil physical properties with the aim of quantifying the influence of a wide range of these properties on water infiltration and identifying the most important factors in selected soils in a semi-arid region.
Materials and Methods:
To investigate the role of soil physical properties on soil water infiltration indices, sixty eight sites in a semi-arid climate of Zanjan province were selected. To capture sufficient variability for examining the effects of physical factors on soil water infiltration, the sites were chosen based on criteria such as land use type, vegetation cover, soil texture, ensuring that the experiments were conducted on the predominant soils of the region. At each sampling site, fourteen consecutive readings of infiltration depth were recorded at specific time intervals until the infiltration rate reached to a steady state flow, for the calculation of various soil water infiltration indices. To evaluate soil water infiltration in detail, six key indices including cumulative infiltration (CI), initial infiltration (II), initial infiltration rate (IIR), final infiltration rate (FIR), mean infiltration rate (MIR), and effective infiltration depth (EID) were determined. In addition to field infiltration measurements, disturbed and undisturbed soil samples were collected from 0–60 cm depth soil surface as the active hydrological layer (Brady & Weil, 2017) and transferred to the laboratory. Various soil physical properties consist of particle size distribution (PSD), gravel content, bulk density (BD), initial soil moisture, mean weigt diameter of soil aggregates (MWDdry), MWD and geometric mean diameter of water-stable aggregates (MWDwet and GMDwet) were determined in the samples.
Results:
Pearson correlation analysis revealed that the mean weight diameter (MWDwet) and geometric mean diameter (GMDwet) of water-stable aggregates were significantly correlated with all infiltration indices (p< 0.05). Bulk density also exhibited significant correlations with CI, II, FIR, and MIR (P< 0.05). Moreover, the multiple regression results indicated that the physical properties including BD, initial soil moisture, gravel content, PSD, and GMDwet are the main factors controlling water infiltration in the soils. The regression results indicated that the physical properties including BD, initial soil moisture, gravel, particle size distribution and GMD are the main factors controlling water infiltration. In order to the one-way analysis of variance, the soils were classified at four groups in BD, MWDwet and GMDwet. Significant differences were found among GMDwet groups in CI, II and FIR (p< 0.05). Diffences among different groups of MWDwet in CI and II wear significant. Additionally, significant differences were among the BD groups in CI. This study indicated that along with soil structure, particle size distribution of soils can affect of soil structure as well as porosity and in return impact on water infiltration in semi-arid soils.
Conclusion:
The results showed that mean weigt diameter and geometric mean diameter of water-stable aggregates (MWDwet and GMDwet) along with bulk density (BD) have the highest correlations with soil water infiltration indices. These three soil physical properties are considered to be the most important determining factors in explaining soil water infiltration. It was also found that particle size distribution (PSD) influences indirectly MWDwet and GMDwet and BD and in consequence affects soil infiltration behavior. These findings emphasize the importance of PSD and soil structure in the process of soil water infiltration in semi-arid regions. |