## 2 Materials and Methods
### Experimental Design  
The experimental design encompassed four runoff plots: standard runoff plot, strip seeding, hole seeding, and natural vegetation (Figure 2). Each runoff plot represents a distinct experimental factor, having a width of 5 m (parallel to contour lines) and a length of 20 m (horizontally projected), resulting in a horizontal area of 100 m\({}^{2}\). The standard runoff plot was established on smoothly sloping, perennially fallow cultivated land devoid of any vegetation cover throughout the year. Any emerging plants were promptly removed to maintain a bare condition, thus serving as the control (CK) for comparison. All conditions were consistent with the standard runoff plot for the three treatment plots, except for planting perennial sweet peas and allowing natural vegetation growth in separate areas.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Experimental Zones** & **Description** \\ \hline \multirow{7}{*}{Yi County} & The study area is located in the northern segment of the Taihang Mountains in Yi County, specifically in the village of Xiayugezhuang (39\({}^{\circ}\)25\({}^{\prime}\) N, 115\({}^{\circ}\)23\({}^{\prime}\) E; about 130-180 m above sea level). This region is characterized by hilly terrain with slopes typically 15–20 degrees. The soil type is red, with varying thicknesses ranging from 10 to 20 cm, representing a typical low mountain arid region. The region has a temperate continental monsoon climate, with an annual mean temperature of 11.4–11.9 \({}^{\circ}\)C. The climate is characterized by arid conditions, with an annual precipitation of 450–600 mm and annual evaporation of 2100 mm. Approximately 80% of the rainfall occurs during July and August. The frost-free period spans approximately 170 days. \\ \hline \multirow{7}{*}{Suburban Areas of Shijiazhuang City} & The study area was situated in the northwestern outskirts of Shijiazhuang City (114\({}^{\circ}\)26\({}^{\prime}\) E, 38\({}^{\circ}\)0\({}^{\prime}\) N, 84.818 m above sea level elevation), representing the central plain region of the alluvial fan at the foot of the Taihang Mountains. The soil predominantly consists of loamy soil, with a 0–40 cm tillage layer. The region experiences an annual average temperature of 12.8 \({}^{\circ}\)C, an average annual precipitation of 599 mm, 2758 h to synthesize annually, and a frost-free period lasting 194 days. \\ \hline \multirow{7}{*}{Zhuolu County} & The study area was 1.5 km south of Zhuolu County, Zhangjiakou City (115\({}^{\circ}\)13\({}^{\prime}\) E, 40\({}^{\circ}\)22\({}^{\prime}\) N, elevation 524.6 m). The predominant soil type is sandy loam. It falls within the hilly region and experiences an inland monsoon climate. The annual average temperature is 8.8 \({}^{\circ}\)C, with an annual average rainfall of 390.5 mm and evaporation measures 785.9 mm—strong winds and dry conditions in spring, indicating a semi-arid to arid climate. Rainfall is concentrated mainly between July and September, with an annual average of 2875 h of sunshine and a frost-free period lasting 140 days. \\ \hline \multirow{7}{*}{She County} & The study area was in the southern part of the Taihang Mountains, in Hui Li, She County, Handan City (113\({}^{\circ}\)26\({}^{\prime}\) E, 36\({}^{\circ}\)17\({}^{\prime}\) N, elevation 750.6 m). It falls within a mountain basin; the predominant soil type is sandy loam. The climate in this region is characterized as an inland monsoon climate with a prevalence of strong winds and dry conditions in the spring. The average temperature is 13 \({}^{\circ}\)C, with an annual rainfall of 560 mm. Rainfall is concentrated mainly between July and September, and the frost-free period lasts 185 days. \\ \hline \hline \end{tabular}
\end{table}
Table 1: Overview of natural conditions in the experimental zones for perennial sweet pea introduction.  
Additionally, soil infiltration tests were carried out in the areas cultivated with four-year-old perennial sweet peas, and these results were subsequently compared with those of the control plots (CK).