Soil water infiltration rate, together with rainfall rates determine runoff rates, being an important parameter for erosion estimation and soil conservation studies. Measurement of infiltration rates can be performed using a double-cylinder device (CD) or a rotating-boom rainfall simulator (RS). The use of CD is less laborious in comparison with RS instruments, but results often do not agree with rates occurring in real rainfall situations, possibly due to surface crust formation. Crust formation depends both on factors that do not depend on soil management, such as rainfall intensity and soil texture and on factors that do depend on soil management, mainly soil strength and crop residue cover. In situations where crust formation is likely to occur, infiltration rates measured by CD will probably overestimate real infiltration rates occurring during rainfall events. To verify if there is a correlation between soil management and the ratio between infiltration rates determined using RS and CD, infiltration rates were measured by both methods on two Ultisols in southern Brazil. Plot treatments differed in crop residue cover and removal or not of preexisting crust. RS measurements were made using a rotating-boom rainfall simulator with a Veejet 80100 nozzle over 3.5 x 11.0 m plots, generating a rainfall intensity of 64.2 mm h-1 during 100 to 150 minutes. Plots were bordered by steel plates and runoff was collected at the lower border for 3 seconds every 3 minutes. The CD was composed of an inner and an outer cylinder (diameter 0.30 m and 0.60 m, respectively), driven into the soil to a depth of 0.10 m, shortly before RS determinations. The area inside the cylinders was flooded and infiltration rates within the inner cylinder were registered at regular time intervals, making three replicates per plot. Results showed CD measured final infiltration rates to be five to tenfold greater than RS. CD measurements are closer to RS measurements when soil cover is present. Instant infiltration rates are more similar when no preexisting surface crust exists. These results show that infiltration rates determined by CD and RS cannot be used in soil conservation studies without correction and that correction factors should consider management conditions, especially those related to soil crust existence and formation, and presence of residue cover.
Infiltration rate; double cylinder device; rainfall simulator; surface crust, surface degradation, erosion