Effects of Hillside Grass Distribution Patterns on Soil Erosion and the Particle Size Distribution of Sediments Under Different Rainfall Intensities

The distribution patterns of grass cover on arid and semi-arid slopes significantly influence runoff and erosion processes. However, the mechanisms by which these patterns affect hydrological and erosion processes, and the subsequent selective transport of sediment particles, remain poorly understood. To address this knowledge gap, this study conducted rainfall experiments of varying intensities (60, 90 and 120 mm h⁻¹) across different grass distribution patterns—random (RP), checkerboard (CP), vertical strips (VP), step strips (SP), banded (BP) and bare slope (BS)—to investigate their effects on runoff, erosion and sediment particle size distribution (PSD). The results show that the BP pattern was most effective in reducing runoff and erosion rates, with reductions of 47.6%–76.5% and 75.4%–84.9%, respectively, compared to BS; SP follows, whereas VP demonstrates the least effectiveness. No significant differences were observed in runoff and erosion rates between the RP and CP treatments. Regarding sediment PSD, the sediments from BS, RP, CP and VP plots predominantly consist of clay and fine silt, accounting for 53.1%–62.8%, whereas sediments from the SP and BP plots are primarily composed of coarse silt (66.9%) and sand (79.2%), respectively. The enrichment of sediment particle size was influenced by the grass distribution patterns. At 60 mm h⁻¹ rainfall, clay and fine silt from BS plots are preferentially enriched as aggregates, while sandy particles are enriched in VP, SP and BP plots; the sediment distributions in RP and CP plots closely resemble that of the original soil. These findings elucidate the impacts of different grass distribution patterns on sediment PSD and provide insights for the development of grass-planting strategies.