Influence of stiff-stemmed grass hedge systems on infiltration

The ability of grass hedge systems to reduce runoff is critical to their effectiveness in controlling soil erosion. The reduction in runoff depends on the infiltration properties of soil managed with hedges. The objective of this study was to evaluate the effects of stiff-stemmed grass hedges on infiltration. The experiment was conducted on a site, which had been managed with switchgrass (Panicum virgatum L.) hedges for 10 yr at the USDA-ARS research station near Treynor, IA. The predominant soil was Monona silt loam (fine-silty, mixed, superactive, mesic Typic Hapludolls). Ponded infiltration measurements were used to determine field-saturated hydraulic conductivity (K-fs). Three positions were sampled: within grass hedges, within a deposition zone 0.5 m upslope from grass hedges, and within a row crop zone 7 m upslope from the hedges in soybean (Glycine max) production during 2001 and corn (Zea mays L.) production during 2002. A tension infiltrometer was used to measure infiltration at three selected tensions (50, 100, and 150 mm) in the grass hedge and row crop positions. The physically based Parlange, the Green and Ampt, and the empirically based Kostiakov infiltration models fit the measured data well (r(2) = 0.99-1.00). The K-fs within the grass hedge position was more than seven times greater than in the row crop position and 24 times greater than in the deposition position. The infiltration rate at 50- and 100-mm tension in the grass hedge position was significantly larger (P < 0.01) than in the row crop position; values at 150-mm tension were not significantly different. The K-fs was found to be similar in magnitude to laboratory measured saturated hydraulic conductivity (K-fs) treated with bentonite to eliminate by-pass flow. Grass hedges were found to enhance water infiltration compared with conventional row crop management.