Abstract
The soil surface roughness increases water retention and infiltration, reduces the runoff volume and speed and influences soil losses by water erosion. Similarly to other parameters, soil roughness is affected by the tillage system and rainfall volume. Based on these assumptions, the main purpose of this study was to evaluate the effect of tillage treatments on soil surface roughness (RR) and tortuosity (T) and to investigate the relationship with soil and water losses in a series of simulated rainfall events. The field study was carried out at the experimental station of EMBRAPA Southeastern Cattle Research Center in São Carlos (Fazenda Canchim), in São Paulo State, Brazil. Experimental plots of 33 m² were treated with two tillage practices in three replications, consisting of: untilled (no-tillage) soil (NTS) and conventionally tilled (plowing plus double disking) soil (CTS). Three successive simulated rain tests were applied in 24 h intervals. The three tests consisted of a first rain of 30 mm/h, a second of 30 mm/h and a third rain of 70 mm/h. Immediately after tilling and each rain simulation test, the surface roughness was measured, using a laser profile meter. The tillage treatments induced significant changes in soil surface roughness and tortuosity, demonstrating the importance of the tillage system for the physical surface conditions, favoring water retention and infiltration in the soil. The increase in surface roughness by the tillage treatments was considerably greater than its reduction by rain action. The surface roughness and tortuosity had more influence on the soil volume lost by surface runoff than in the conventional treatment. Possibly, other variables influenced soil and water losses from the no-tillage treatments, e.g., soil type, declivity, slope length, among others not analyzed in this study.
Highlights
Soil roughness describes the microvariations in surface elevation resulting mainly from management practices and is one of the main factors influencing wind and water erosion (Vidal Vázquez et al, 2005)
The rugosidade superficial (RR) and T values decreased during the rain sequence in both tillage types; T more than RR
The first rain caused the greatest impact on the surface of the soil disturbed by tillage, evidenced by higher RR and T values than before the rain events
Summary
Soil roughness describes the microvariations in surface elevation resulting mainly from management practices and is one of the main factors influencing wind and water erosion (Vidal Vázquez et al, 2005)The onset of runoff roughness can be delayed by the surface roughness, by temporary water storage in the microdepressions of the soil, decreasing the runoff rate and volume and increasing sediment retention and, soil loss by erosion (Allmaras et al, 1966; Cogo et al, 1983; 1984; Onstad, 1984; Darboux & Huang, 2005; Bertol et al, 2006).The occurrence of runoff, and of material transport by erosion, depends on the rainfall volume and intensity, soil water infiltration, surface storage capacity (Cogo, 1981; Battany & Grismer, 2000; Arnáez et al, 2007; Boulal et al, 2011), and terrain slope, among others. The onset of runoff roughness can be delayed by the surface roughness, by temporary water storage in the microdepressions of the soil, decreasing the runoff rate and volume and increasing sediment retention and, soil loss by erosion (Allmaras et al, 1966; Cogo et al, 1983; 1984; Onstad, 1984; Darboux & Huang, 2005; Bertol et al, 2006). The water storage capacity of the soil surface depends almost exclusively on the surface roughness (Cogo, 1981; Kamphorst et al, 2000; Alvarez-Mozos, 2011). With the advances in research on soil erosion processes, the interest in measurement and modeling of the surface microrelief has increased, especially for use in mathematical models of soil loss using the evolution of surface water retention during rainfall events (De Roo et al, 1995; Govers et al, 2000) Rainfall gradually reduces this roughness (Paz González & Castro, 1996; Eltz & Norton, 1997; Kamphorst, et al, 2000; Bertol et al, 2007).
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