INTEGRATED ASSESSMENT AND ANALYSIS OF PHYSICAL LANDSCAPE PROCESSES THAT IMPACT THE QUALITY AND MANAGEMENT OF AGRICULTURAL WATERSHEDS
Location: Watershed Physical Processes Research Unit
Title: How Management of Grass Hedges Affects Their Erosion Reduction Potential
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 3, 2008
Publication Date: January 21, 2009
Citation: Dabney, S.M., Mcgregor, K.C., Wilson, G.V., Cullum, R.F. 2009. How Management of Grass Hedges Affects Their Erosion Reduction Potential. Soil Science Society of America Journal. 73(1):241-254.
Interpretive Summary: Grass hedges are narrow strips of erect growing grass that are effective in slowing rainfall runoff and trapping sediment. We conducted studies on field plots to determine how the effectiveness of grass hedges for trapping eroded sediment changed over time after transplanting and in response to harvest of plant residues created when the hedges were mowed. We learned that grass hedges could reduce soil loss from tilled cropland caused by severe storms by 80 to 90% and that their effectiveness was increased by leaving rather than harvesting the residues created by mowing the hedges. Our observations agreed reasonably well with predictions of the RUSLE2 computer model that the Natural Resources Conservation Service currently used to create farm conservation plans and to determine farm program eligibility, but pointed out areas where the model could be improved.
Grass hedges are specialized vegetative buffers effective in trapping sediment. Information is needed on how the effectiveness of grass hedges changes over time after planting, and in response to hedge clipping management. Erosion from natural rainfall was measured during thirteen years after establishing single-row miscanthus (Miscanthus sinensis, Anderss) hedges at the lower end of erosion plots (21 m long, 5% slope) in a replicated study involving conventional tillage (CT) and no-till (NT) cotton (Gossypium hirsutum L.) grown on silt loam soils (Typic Fragiudalfs) in Holly Springs, MS. Sediment yield values from plots with and without grass hedges were analyzed with reference to the universal soil loss equation (USLE) to determine the conservation support practice (“P” factor) values. The “P” factor of grass hedges was found to be about 0.5 during the establishment year and to decrease progressively with time for CT cotton, averaging 0.23 for CT over 7 yr for wide-row cotton and 0.12 for 5 yr of UNR cotton studied with older hedges. P factors for NT were higher, averaging 0.5 for wide-row cotton and 0.65 for UNR cotton, perhaps reflecting a finer eroded sediment size distribution. Monthly rainfall effects on soil erosion in this study were not fully explained by the EI30 term used in the USLE, but more complex models did not greatly alter the support practice “P” factor estimates of grass hedges. This study demonstrated that during extreme events, hedge effectiveness was enhanced by management that allowed accumulations of hedge clippings upslope of the hedges and that RUSLE2 provides reasonable estimates of hedge effectiveness.