Water erosion in surface soil conditions: runoff velocity, concentration and D50 index of sediments in runoff

ABSTRACT Water erosion and contamination of water resources are influenced by concentration and diameter of sediments in runoff. This study aimed to quantify runoff velocity and concentration and the D50 index of sediments in runoff under different soil surface managements, in the following treatments: i) cropped systems: no-tilled soil covered by ryegrass (Lolium multiflorum Lam.) residue, with high soil cover and minimal roughness (HCR); no tilled soil covered by vetch (Vicia sativa L.) residue, with high soil cover and minimal roughness (HCV); chiseled soil after ryegrass crop removing the above-ground residues and keeping only the root system, with high roughness (HRR); chiseled soil after vetch crop removing the above-ground residues and keeping only the root system, with high roughness (HRV); ii) bare and chiseled soil, with high roughness (BHR). The research was conducted on a Humic Dystrupept under simulated rainfall. The design was completely randomized and each treatment was replicated twice. Eight rainfall events of controlled intensity (65 mm h−1) were applied to each treatment for 90 minutes. The D50 index, runoff velocity and sediment concentration were influenced by crop and soil management. Runoff velocity was more intensely reduced by cover crop residues than by surface roughness. Regardless of surface condition, the D50 index and concentration of sediment in runoff were lower under ryegrass than vetch crop. Runoff velocity and the D50 index were exponentially and inversely correlated with soil cover by residues and with surface roughness, while the D50 index was positively and exponentially correlated with runoff velocity.

摘要 水体侵蚀与水资源污染程度受径流中沉积物的浓度与粒径影响。本研究旨在量化不同土壤地表管理措施下的径流流速、径流沉积物浓度以及径流沉积物的D50指标，试验设置如下处理组：i）种植系统：免耕并被黑麦草（Lolium multiflorum Lam.）残体覆盖、高土壤覆盖度且低地表粗糙度（HCR）；免耕并被箭舌豌豆（Vicia sativa L.）残体覆盖、高土壤覆盖度且低地表粗糙度（HCV）；黑麦草收获后进行凿式耕翻，移除地上残体仅保留根系、高地表粗糙度（HRR）；箭舌豌豆收获后进行凿式耕翻，移除地上残体仅保留根系、高地表粗糙度（HRV）；ii）裸地凿式耕翻处理，高地表粗糙度（BHR）。本试验在腐殖质暗色湿润始成土（Humic Dystrupept）上开展，采用模拟降雨方式进行。试验采用完全随机设计，每组处理重复两次。每组处理均施加8次强度可控（65 mm·h⁻¹）的模拟降雨，每场降雨持续90分钟。径流沉积物的D50指标、径流流速与沉积物浓度均受作物与土壤管理措施的影响。与地表粗糙度相比，覆盖作物残体对径流流速的降低效果更为显著。无论地表条件如何，黑麦草处理组的径流沉积物D50指标与沉积物浓度均低于箭舌豌豆处理组。径流流速与D50指标分别与残体土壤覆盖度、地表粗糙度呈指数负相关；而D50指标与径流流速呈指数正相关。