|Eltz, F - SANTA MARIA, RS BRAZIL|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 1996
Publication Date: N/A
Interpretive Summary: Tillage of the soil leaves a certain amount of roughness, depending on the type of tillage and soils present. When rain occurs, the tillage roughness decreases and erosion occurs. This study was conducted to determine how much roughness is needed to prevent erosion prior to the development of soybean cover, and then how soybean canopy protects roughness from decaying due to raindrops. Different types of roughness indices were used to quantify the changes in roughness over time in order to determine which was best to quantify the changes. Soybean canopy was found to influence roughness changes only slightly. Therefore, it was determined that for roughness to be effective as a soil conservation factor, considerable initial roughness is needed to prevent erosion.
Technical Abstract: Surface roughness and canopy cover are important factors in preventing soil erosion. There is a limited amount of information on how soil surface roughness changes (dR) as a function of natural rainfall erosivity and how much canopy cover by plants affects dR. The effects of different canopy cover and tillage systems, and cumulative rainfall erosivity on dR were investigated in a field study on a Miami silt loam soil (fine-silty, mixed, mesic Typic Hapludalf) using a portable laser microtopographer. Tillage treatments included conventional (moldboard plowing + disking), chisel plowing, and chisel plowing + dragging a chain to produce three levels of initial roughness. Surface cover treatments consisted of fallow and soybeans. Four soil surface roughness indices were calculated from microtopography data: random roughness (RR), standard deviation (SD), tortuosity (T) and fractal roughness functions, expressed by D (fractal index) and l. As a general trend, all indices but D decreased with cummulative rainfall erosivity. RR and SD indices decreased quadratically with cummulative rainfall erosivity, while T and l indicies decreased exponentially. Soybean cover provided a decrease of only 7 percent in dR, as measured by the l index, when compared with fallow. The l indices were more sensitive to changes in cummulative rainfall erosivity. The fractal roughness functions, with D and l indices calculated, were the best approaches to characterize dR at small scales.