Effects of root density on soil detachment capacity by overland flow during one growing season

Objective Roots can effectively reduce soil detachment. However, the dynamics of different root effects on soil detachment with root growth time are not clearly understood. Therefore, our objectives were to characterize the dynamics of soil detachment with root growth time and compare the effectiveness of roots of different types and planting densities on soil detachment. Materials and methods A laboratory experiment was conducted to quantify and elucidate the effect of fibrous ryegrass ( Lolium perenne L. ) roots and alfalfa ( Medicago sativa L. ) taproots on soil detachment, with two planting densities at 4 different growth stages. Root parameters, soil properties, and the soil detachment rate (with a flow discharge of 3 L min −1 for 15 min on a 15° slope) were measured at days 28, 56, 84, and 112. Results and discussion Root parameters increased with root growth time, and the fibrous roots varied more significantly than taproots. Soil bulk density decreased with root growth time, while the contents of soil organic matter and water-stable aggregates increased with root growth time. The effect of fibrous roots on soil properties was significantly greater than that of taproots. The absolute soil detachment rate and relative soil detachment rate from fibrous roots decreased by 53.35% and 51.98% from days 28 to 112 respectively, but those from taproots did not change significantly. Soil detachment under high-density cultivation was lower than that under low-density cultivation at the early growth stage but inversely later. Soil detachment decreased exponentially with root parameters, and the equation of root parameters and soil detachment in RL (ryegrass with a low planting density) best explained the soil detachment variation (91.3–96.1%). Conclusions Plants with fibrous roots had greater effect on soil detachment reduction than those with taproots. Treatments with high planting density had a more significant influence on soil detachment reduction than did those with low planting density at the early growth stage, but the opposite was true later. This experiment helped to explain the mechanism and process of root growth affecting soil detachment and provided a fundamental basis for erosion management practices. Graphical abstract