Sediment transport in runoff on rugous soil surface submitted to simulated rainfall

Abstract

Soil management influences water erosion and sediment size in runoff. With the objective of quantifying sediments in runoff and their relation to runoff velocity (Rv), random roughness (RR), and Ir index, this experiment was carried out from 2003 to 2006, on a typical Hapludox with the following soil management systems submitted to chiseling: i) bare soil with plowing+two disking tillage (BSC); ii) plowing+two disking tillage (CTC); iii) no tillage with crop residues burned (BNTC); and iv) traditional notillage (TNTC). CTC, BNTC and TNTC treatments were cultivated with crop rotation and the BSC treatment was not cultivated. Five simulated rainfall tests were applied, with intensity of 64 mm h -1 and duration of 20, 30, 40, 50 and 60 min. RR was influenced by the residual effect of soil management and by simulated rainfall, and affected the Rv in the three initial rainfall tests. Sediments carried by runoff were influenced by soil management and by simulated rainfall. Most of the sediments were in the size range from 0.5 to > 2 mm, with a higher quantity of fine sediment in BNTC and TNTC treatments than in the other treatments. The D 50 index of sediments changed with soil management system and with rainfall tests, decreasing with the increase of the RR and increasing with the increment of Rv and Ir index.

Water erosion in no-tillage monoculture and intercropped systems along contour lines

“…Over the course of the rainfall tests which were applied during the crop cycle, the soil losses sometimes increased, decreased, remained stable or oscillated, independently of the water loss (Table 3), according to Bertol et al (2010). This erratic soil loss data behaviour is normal, in agreement with the variation in sediment concentration in the runoff (data not presented here), as also shown by Bertol et al (1997), Luciano et al (2009) and Gobbi et al (2011).…”

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

“…The D 50 index showed an inverse exponential relationship with soil cover and surface roughness ( Figure 2), agreeing with Bertol et al (2010) and Panuska et al (2008). For the treatments with surface residues, HCR and HCV, the coefficients of determination between the D 50 index with soil coverage were 0.73 and 0.47, respectively (Figure 2A).…”

“…Regardless of the treatment, RV increase was exponentially correlated with the increase in the D 50 index (Figure 3), showing that RV increased sediment transport capacity, also verified by Bertol et al (2010). The adjustment degree of these variables was higher in the HRR and HCR treatments in which the D 50 index was explained by RV 79 % and 88 % respectively, compared to HCV and HRV, where the relations were 50 % and 25 %, respectively.…”

“…This RV reduction is important since it has great influence on the final flow energy, thus, on its capacity to detach and transport coarse soil particles and aggregates (Lambrechts et al, 2013). In bare soil (BHR), the exponential model was weakly adjusted to the data and this treatment had the lowest efficiency to reduce RV due to its low soil aggregate resistance, resulting in fast flattening and sealing of soil surface, which accelerate and increase runoff flow energy, as reported for this soil condition by Bertol et al (2010).…”

“…The determinations were always carried out in the same place in the plot, marked by wooden stakes also used to level and support the micro relief meter. Surface roughness was obtained through a photographic record of a 20-bar set, where the bar heights in the photographs, representing the micro relief, were obtained by image interpretation, as described by Bertol et al (2010). The random roughness index (RR) was calculated using the method proposed by Kamphorst et al (2000) with no transformation of the data into logarithms or elimination of the extreme values.…”