Evaluating Maintenance Techniques for Long-Term Vegetation Establishment on Disturbed Slopes in Alabama
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Sustainability of common bermudagrass on formerly disturbed slopes in Alabama has proven to be a difficult task in some cases. Failures of once successful stands of bermudagrass can be seen throughout Alabama on road banks, borrow areas, and other formerly disturbed slopes. Failure of the permanent vegetation results in exposed soil subject to erosion as well as off-site sediment transport. In this research, selected maintenance techniques and environmental impacts are evaluated using outdoor plots of third year common bermudagrass. Part one of this research was conducted in 2010 at the E. V. Smith Research Center (EVSRC) located in Milstead, Alabama, and focuses on mowing height and herbicide application effectiveness to improve bermudagrass regrowth, as measured by Δ percent bermudagrass cover, while monitoring runoff for corresponding effects on turbidity and selected nutrient concentration. Mowing height treatments of 7.6 cm, 15.2 cm, and 22.9 cm (3, 6, and 9 in, respectively) were evaluated with and without herbicide application treatments. The 7.6 cm mowing height was found to significantly increase bermudagrass regrowth by 12 percent cover between individual cuttings. The 15.2 cm mowing height was found to significantly increase bermudagrass regrowth by 12 percent cover across the entire growing season. Herbicide application significantly increased bermudagrass regrowth compared to no-herbicide treatments with an increase of 6 percent cover over the entire growing season. Average turbidity values across all treatments and sampling dates was 28 NTUs. Mean nitrate, ammonium, and phosphate concentrations in runoff ranged from 0 to 5.3 mg/L, 0 to 4.0 mg/L, and 0 to 6.5 mg/L, respectively. There were no significant differences in turbidity values or nitrate, ammonium, and phosphate concentrations in runoff in response to mowing height or herbicide application treatments. Although the mowing height by herbicide interaction was not significant, it was concluded from this study that the herbicide applied 15.2 cm treatment was most conducive to increasing bermudagrass regrowth for long-term sustainability. Part two of this research focused on a separate study located at the Turfgrass Research Unit (TGRU) located in Auburn, Alabama, to compare new digital image analysis (DIA) vegetation cover estimates with conventional line transect method cover estimates. The comparative study was performed on initial establishment of TifSport bermudagrass. Bermudagrass grow in data as a percent cover was collected using both the DIA and line transect methods and subsequently analyzed for correlation. A limited accuracy assessment of the DIA method using five digital photographs of calculated percent cover concluded that the DIA method adequately estimates vegetation cover (r = 0.999) compared to field measured grids of bare soil and bermudagrass. Independently collected paired line transect and DIA data on 52 plots at TGRU (n=352) did not express high correlation (r = 0.75). The line transect method over-estimated vegetation cover by 23%. It was concluded based on the higher correlation of the calibration study (1.00 vs. 0.75) that most of the variability in the paired data at TGRU was a result of observer subjectivity within the line transect method. Minimal DIA variability appeared to result from inter-pixel confounding. When comparing DIA to the line transect method estimates, results similar to Richardson et al. (2001) and Godinez-Alvarez et al. (2009) were found. The line transect method over estimated vegetation cover compared to the DIA method. Therefore, it was concluded from this study that DIA more adequately estimates vegetation cover than the line transect method. Results from this study affirm the importance of proper maintenance procedures for sustainability of common bermudagrass on formerly disturbed slopes in Alabama, and indicate the need for further research for a better understanding of bermudagrass response to maintenance techniques. Findings in this study also demonstrate the need to further evaluate DIA as a means to quantify vegetation cover with a larger accuracy assessment.