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.
Highlights
Understanding the effect of water flow velocity, concentration and diameter of sediments in runoff is necessary to predict water erosion, mainly, the runoff capacity to transport chemicals that can contaminate water resources (Kuhn et al, 2012)
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 greatest random roughness index (RR) observed in HRR after chiseling is due to a higher aggregation provided by ryegrass roots compared to vetch
Summary
Understanding the effect of water flow velocity, concentration and diameter of sediments in runoff is necessary to predict water erosion, mainly, the runoff capacity to transport chemicals that can contaminate water resources (Kuhn et al, 2012). Soil surface characteristics with greater influence on water erosion, related to runoff velocity and concentration and diameter of eroded sediments, are soil cover by crop residues and soil surface roughness (Cogo et al, 1984; Engel et al, 2009). These characteristics are usually found in conservative soil tillage (Bertol et al, 2003), represented by no-till and minimum tillage. Roughness increases surface tortuosity and, decreases runoff velocity and its ability to detach the soil and transport sediments (Rodríguez-Caballero et al, 2012), this effect is ephemeral
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