Techniques for Establishing Vegetation for Erosion Control on Disturbed Slopes in Alabama

Abstract

Soil erosion is a serious issue in the revegetation of disturbed slopes that occurs during highway and other construction. Although slope disturbance from highway construction is widespread, there is little information about proper fertilization or seeding methods for revegetation of those disturbed slopes. The study objectives were to evaluate: 1) the effect of incorporating lime and fertilizer on establishment of bermudagrass, 2) differences in bermudagrass establishment related to temporary covers, including wheat straw, erosion control blankets, and hydromulch, and 3) effects of cover treatments including polyacrylamide (PAM) on runoff volume and quality. Twenty-one (3m×8m) plots were used to compare six cover treatments to seeded no- cover control plots. Treatments used in the study were: 1NC – seeded no-cover; 1ECB - erosion control blanket; 1GM and 2GM - hydromulch with and without pre-incorporation of fertilizer; 1GMP and 2GMP – hydromulch plus PAM with and without pre-incorporation of fertilizer; and 1WS - wheat straw. At the end of the 13-month study, erosion control blanket had the highest runoff compared to the no-cover control but loose straw and hydromulch had the lowest runoff relative to the no cover control. Observed average percent bermudagrass cover ranking at approximately 60 days after planting was (greatest to least cover): 1GM (66%), 2GMP (60%), 2GM (59%), 1GMP (49%), 1ECB (44%), 1WS (29%), and 1NC (20%). Adding polyacrylamide (PAM) to hydromulch did not significantly improve bermudagrass establishment. However, hydromulch treatments had more rapid bermudagrass establishment as compared to that measured in erosion control blanket, loose straw, or seeded control plots. When averaged over the first 90 days after planting, some differences in bermudagrass establishment became apparent. First, PAM application had no effect on bermudagrasss establishment. Second, within the hydromulch treatments, the incorporation of lime and fertilizer (versus surface application) did not affect bermudagrass establishment. Third, bermudagrass was established significantly quicker when a hydromulch was used as compared to an erosion control blanket, or loose straw. Filtered turbidity of runoff (relative to no cover control) indicated the following ranking (most effective to least effective): Loose straw, hydromulch, and erosion control blanket. The reduction in sediment loss from cover treatments compared to control plots ranged (most effective to least effective) from 22% to 98% for loose straw , 22% to 93% for hydromulch , 16% to 92% for erosion control blanket. Average annual sediment loss reductions compared to no cover control plots were 66% for loose straw, 58% for erosion control blanket, and 53% for hydromulch. Addition of PAM in the hydromulch treatment significantly reduced MTSS early in the year-long test in three of the first four storm events. Inclusion of PAM did not significantly reduce NTU at any sampling date. However, incorporation of lime and fertilizers into the soil before planting did not. Addition of PAM to hydromulch treatments decreased the concentration of nitrate in runoff, but incorporating lime and fertilizer did not. Runoff from the no-cover control contained the highest phosphate the first 120 days after planting, followed by the erosion control blanket, hydromulch, and loose straw. However, these differences were not significantly different from each other. Incorporating lime and fertilizer or adding PAM did not significantly affect the concentration of phosphate in runoff. Findings of this study emphasize the environmental importance of temporary covers on disturbed slopes during the first critical months of establishment, and indicate the need for continued studies for more definite evaluation of each method under different soil growing conditions.