Deciphering runoff and soil loss processes during various phenological stages of Trifolium pratense at small plot scale

Land degradation occurs primarily through soil erosion and hydrological instability. The role of vegetation growth stages, specifically germination, greening, flowering, live root, and dead root, in runoff and soil erosion control lacks sufficient investigation. The current research, therefore, examines runoff and soil loss during five successive growth stages of Trifolium pratense, which functions as an essential forage species for rangeland rehabilitation under simulated rainfall conditions. The study executed controlled laboratory experiments using soil collected from the Kojour Watershed, northern Iran. The experiment utilized rainfall simulations (50 mm h⁻¹ intensity, 20% slope, 30-min duration) on vegetated and bare (control) plots to mimic regional rainfall conditions while maintaining statistical control for robust comparative assessments. The experimental data show that vegetated plots yielded more favorable results by generating 1.27–1.65 times less runoff volume and lowering soil loss by factors of 1.15–4.99 times. The flowering stage demonstrated maximum erosion control because its roots and canopy reached their peak developmental stage. The results also showed that the above-ground plant biomass primarily controlled splash erosion, but the roots basically strengthened the soil via binding and bonding effects to achieve stabilization. The research showed that vegetation primarily assists by stopping soil detachment rather than significantly affecting runoff. The study exclusively focused on T. pratense, so additional research should investigate whether these findings apply to other plant species. Research success will improve runoff and soil erosion-controlling strategies and be a starting point for further studies on rangeland species functions.