The effectiveness of stiff‐stemmed grass hedge systems in controlling runoff and soil erosion is influenced by the water transport properties of the soil under grass hedge management. This study evaluated soil hydraulic properties within a grass hedge system 10 yr after establishment. The study was conducted at the USDA‐ARS research station near Treynor, IA in a field managed with switchgrass (Panicum virgatum) hedges. The soil was classified as Monona silt loam (fine‐silty, mixed, superactive, mesic Typic Hapludolls). Three positions were sampled: within the grass hedges, within the deposition zone 0.5 m upslope from the grass hedges, and within the row crop area 7 m upslope from the hedges. Intact soil samples (76 by 76 mm) were taken from the three positions at four depths (100‐mm increments) to determine saturated soil hydraulic conductivity (Ksat), bulk density (ρb), and soil water retention. The grass hedge position had significantly greater (P < 0.05) macroporosity than the row crop and deposition positions in the first two depths and greater than the deposition position in the last two depths. The Ksat within the grass hedge (668 mm h−1) was six times greater than in the row crop position (115 mm h−1) and 18 times greater than in the deposition position (37 mm h−1) for the surface 10 cm. Bulk density and macroporosity were found to provide the best two‐parameter regression model for predicting the log‐transformed Ksat (R2 = 0.68). These results indicate that grass hedges significantly affected soil hydraulic properties for this loess soil.

Planting stiff‐stemmed grass hedges in a watershed may reduce water runoff and soil erosion, in part by altering soil macroporosity. The objective of this study was to characterize macroporosity of soils under a perennial grass hedge system for 12 yr using x‐ray computed tomography (CT) and to compare CT‐macroporosity results with macroporosity estimated from water retention data. Three positions were sampled: grass hedge position, deposition zone position 0.5 m upslope from grass hedges, and row crop position 7 m upslope from the hedges. Intact core samples (76 mm × 76 mm) were collected from two depths, 0 to 100 and 100 to 200 mm, with five replicates per position per depth. Number of pores (macro‐ and meso‐), averaged across depths, in the grass hedge were nearly 2.5 times greater than those in the row crop and five times greater than in the deposition positions; however their circularity was 8.8% lower than in the row crop and 2.6% lower than in the deposition positions. The CT‐measured macroporosity was significantly greater (P < 0.01) for the grass hedge position (0.056 m3 m−3) as compared with the row crop (0.014 m3 m−3) and deposition positions (0.006 m3 m−3). The fractal dimension (D) was significantly greater (P < 0.01) for the grass hedge position (D = 1.56) than in the row crop (D = 1.31) and the deposition (D = 1.12) positions. The values of all measured pore characteristics decreased with depth. Computed tomography‐measured macroporosity data were comparable with macroporosity estimated from water retention data. These findings suggest that grass hedge systems have created more pores and a greater volume of macroporosity.

Crop rotations and manure application are thought to alter soil quality. This study was conducted to quantify the effects of over 100 yr of continuous crop management and annual manure applications on selected soil physical properties at Sanborn Field, Columbia, MO. Intact soil cores (76 mm i.d. by 76 mm) were collected from continuous corn (Zea mays L.), continuous wheat (Triticum aestivum L.), continuous timothy (Phleum pratense L.), and a rotation of corn–wheat–red clover (Trifolium pratense L.). The soil was Mexico silt loam (fine, smectitic, mesic, Aeric Vertic Epiaqualfs). Soil was tested throughout a 1‐yr period for aggregate stability, single‐drop rainfall splash detachment, and soil shear strength. Cropping systems affected aggregate stability (P < 0.01), soil strength (P < 0.01), and splash detachment (P < 0.01), but not bulk density. Continuous cropping to timothy produced soil that had three to four times greater aggregate stability, 21 to 27% greater soil strength, and 55 to 67% less soil splash compared with continuous wheat or continuous corn. Season significantly affected all measured soil properties, but the effect was inconsistent. The highest aggregate stability was found during July for all treatments. Splash detachment was more sensitive to cropping systems than other soil measures, and thereby the best measure for evaluating changes in soil erodibility. Cropping and soil management that accumulate plant residues can improve soil quality by increasing soil aggregate stability, shear strength, and resistance to splash detachment.

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 (Kfs). 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 (r2 = 0.99–1.00). The Kfs 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 Kfs was found to be similar in magnitude to laboratory measured saturated hydraulic conductivity (Ksat) treated with bentonite to eliminate by‐pass flow. Grass hedges were found to enhance water infiltration compared with conventional row crop management.

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Grass hedges planted at regular intervals on the landscape offer many opportunities to reduce runoff and sediment from leaving fields. Objectives of this study were (1) to evaluate the ability of the WEPP watershed model to simulate grass hedge system effects of sediment trapping (TE), bench terracing (BT), and variable effective soil hydraulic conductivity (HC) on simulated hillslope runoff and sediment yield, and (2) to model the effects of measured effective hydraulic conductivity (K eff) values from a grass hedge management system by comparing predicted runoff and sediment yield values to those measured in a small watershed over an 11-year period. The study was conducted on a 6.6 ha watershed located in the deep loess hills region of southwestern Iowa. Narrow grass hedges of predominantly switchgrass (Panicum virgatum) were planted at 15.4 m intervals in 1991. The WEPP model simulated greater reductions in runoff (9%) and sediment yield (58%) from BT compared to TE and HC effects. Combination of all three effects gave the highest reductions in runoff (22%) and sediment yield (79%) compared to individual effects or any combination of two effects. The watershed model did not adequately simulate slope length reduction effects from the grass hedges. Runoff (r 2 = 0.78) and sediment yield (r 2 = 0.75) were comparable to observed data when measured K eff values for grass hedge, row crop, and channel areas were used as input data. Measured K eff data from grass hedge, row crop, and channel areas should be used for improved runoff and sediment yield predictions.

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