Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2003
Publication Date: 7/1/2004
Citation: Rachman, A., Anderson, S.H., Gantzer, C.J., Alberts, E.E. 2004. Soil hydraulic properties influenced by stiff-stemmed grass hedge systems. Soil Science Society of America Journal. 68 (4):1386-1393.
Interpretive Summary: Narrow rows of stiff-stemmed grass hedges planted within a field can trap sediment near the source of soil detachment reducing the total sediment load leaving the field in surface runoff. In the early 1990s, grass hedge research was initiated in the U.S. based upon reports and observations from India, the West Indies, Fiji, and Indonesia of tremendous sediment deposition immediately upslope of grass hedges. One of the sites chosen for this new research was a 15-acre watershed located in the deep loess hills of western Iowa, an area with severe erosion problems. In May 1991, eight rows of Switchgrass were planted on 50-foot intervals to accommodate 16 rows of corn between each pair of hedges. The planting width of each hedge was 2.3 ft. The objective of this study was to measure the impact of grass hedges on soil properties influencing rainfall infiltration and water movement 10 years after establishment. In June 2001, soil samples were collected within the hedge, in the sediment deposition area above the hedge, and further upslope where soil is detached and moved downslope. The porosity of the soil and the rate that water moved through it were measured in the laboratory. Results showed that water movement through the soil collected in the Switchgrass hedge was 5.8 times higher than in the soil collected upslope of the depositional area. Soil collected in the depositional area had the lowest rate of water movement, probably from silt particles plugging natural soil pores. The rate of water movement through the soil collected in the depositional area was reduced by 68 and 94% when compared to the soil upslope and within the grass hedge, respectively. Results from this study will lead to improved runoff and soil loss prediction equations and models for grass hedge systems that will benefit soil conservationists and water quality specialists.
Technical Abstract: The effectiveness of stiff-stemmed grass hedge systems to control runoff and soil erosion depends on the water transport properties of the soil under grass hedge management. The objective of this study was to evaluate soil hydraulic properties within a grass hedge system 10 years after establishment. The study was conducted within a 6-ha watershed located in western Iowa that had been managed with switchgrass (Panicum virgatum) since 1991. The soil was a Monona silt loam (fine-silty, mixed, 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 under soybean (Glycine max) production. Intact soil samples (76 mm x 76 mm) were collected from the three positions at four depths (100-mm increments) to determine saturated soil hydraulic conductivity (Ksat), bulk density, and soil water retention. The grass hedge position had significantly (P<0.01) greater macroporosity (estimated from water retention data) at all measured depths and greater coarse and fine mesoporosity in the 0- to 20-cm depth compared to the deposition position. Ksat was higher (P<0.01) in the hedge position in the 0- to 20-cm depth compared to the other positions. Bulk density was lower (P<0.01) in the hedge position for the 0- to 20-cm depth compared to the row crop and deposition positions. The Ksat in the grass hedge (668 mm/h) was six times higher than in the row crop (115 mm/h) and 18 times higher than in the deposition position (37 mm/h)for the surface 10 cm. Bulk density and macroporosity were found to be the best two-parameter regression model for predicting the log-transformed Ksat (R**2 = 0.68). Results indicate that grass hedge systems significantly affected soil hydraulic properties for this loess soil.