Soil moisture characteristic curves (SMCCs) play a crucial role in understanding and managing soil-water relationships, which is vital in various fields including agriculture, civil engineering, environmental science, and hydrology. This study investigates the impact of livestock grazing, slope location, and sampling depth on SMCCs in the Gonbad watershed, western Iran. Livestock grazing practices were compared between free grazing and controlled grazing, along with three slope positions (shoulder, back, and foot-slope) and two sampling depths (0−12.5 cm and 12.5−25 cm). The van Genuchten model was employed to model the SMCC, incorporating Mualem's assumption. Water content at different matric suctions and van Genuchten model parameters were assessed using a factorial design. Integral root mean square difference (IRMSD) and surface difference (SD) parameters were calculated to evaluate the impact of different treatments on the SMCC, as a whole. The controlled grazing treatment at the back-slope recorded the lowest residual water content, measuring 0.151 cm³ cm⁻³ in the 0.00- to 12.5-cm depth. Conversely, the highest value of 0.234 cm³ cm⁻³ was observed in the free grazing treatment at the shoulder, specifically in the 12.5- to 25-cm depth. The results indicate that the permanent wilting point (PWP) value at the second depth exceeded that of the first depth. Specifically, at the second depth, the PWP value in the shoulder region of the slope under free grazing (0.235 cm³ cm⁻³) surpassed that of the corresponding position under controlled grazing (0.192 cm³ cm⁻³). The findings revealed that the highest α parameter value (0.438 cm) was observed at the first depth of the back-slope position under the controlled grazing treatment. Results indicated significant effects of grazing, slope position, and sampling depth on soil properties and SMCC parameters. Notably, controlled grazing led to higher values of IRMSD (0.178 cm³ cm⁻³) and SD (0.672 cm³ cm⁻³), indicating enhanced moisture retention capabilities compared with free grazing. The study provides valuable insights into optimizing grazing practices for sustainable soil health and water management in pasture ecosystems.

中文翻译：

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研究牲畜放牧、坡位和采样深度对土壤水分特征曲线的长期影响

土壤湿度特征曲线（SMCC）在理解和管理土壤-水关系方面发挥着至关重要的作用，这在农业、土木工程、环境科学和水文学等各个领域都至关重要。本研究调查了伊朗西部贡巴德流域牲畜放牧、斜坡位置和采样深度对 SMCC 的影响。比较了自由放牧和控制放牧之间的牲畜放牧实践，以及三个斜坡位置（肩坡、背坡和脚坡）和两个采样深度（0−12.5 cm 和 12.5−25 cm）。采用 van Genuchten 模型对 SMCC 进行建模，并结合了 Mualem 的假设。使用因子设计评估不同基质吸力和 van Genuchten 模型参数下的水含量。计算积分均方根差（IRMSD）和表面差（SD）参数来评估不同处理对 SMCC 的整体影响。后坡控制放牧处理的残余水含量最低，在 0.00 至 12.5 厘米深度处测量为 0.151 cm3 cm3。相反，在肩部自由放牧处理中，特别是在 12.5 至 25 厘米深度处观察到最高值，为 0.234 cm3 cm -3 。结果表明，第二深度的永久萎蔫点（PWP）值超过了第一深度的值。具体而言，在第二深度处，自由放牧下坡肩区域的PWP值（0.235 cm3 cm -3 ）超过了控制放牧下相应位置的PWP值（0.192 cm3 cm -3 ）。结果表明，在控制放牧处理下，在后坡第一深度处观察到最高的α参数值（0.438 cm）。结果表明放牧、坡位和采样深度对土壤性质和 SMCC 参数有显着影响。值得注意的是，控制放牧导致IRMSD（0.178 cm3 cm3）和SD（0.672 cm3 cm3）值更高，表明与自由放牧相比，保湿能力增强。该研究为优化放牧实践以实现牧场生态系统的可持续土壤健康和水管理提供了宝贵的见解。