Total Nitrogen Losses From Fertilized Turfs On Simulated Highway Slopes In Florida

Fertilized highway slopes constitute nonpoint sources of nitrogenous nutrients that are degrading the surface water and groundwater resources. This paper presents the results of simulated rainfall experiments conducted on a plot-scale test bed (slope-adjustable) that was fully exposed to weather for closely representing the conditions of a fertilized turf-covered highway slope in Florida. Thirty-six tests were conducted on three slopes (25, 33, and 50%), simulating two rainfall intensities (12.5 and 25 mm/h). The soils used were fine sand (AASHTO A-3 class) and silty sand (AASHTO A-2-4 class). Following the local highway practices, the tests were conducted after compacting the soils and establishing Argentine Bahia turf over A-3 soils and Pensacola Bahia turf over A-2-4 soils. Two fertilizers were used: a quick release (QR) 10-10-10 and a slow release (SR) 16-0-8. Weather conditions varied considerably during the duration of the project, affecting soil moisture, soil - grass - nutrient interactions, and the distribution of applied rainfall. These weather effects and differences in soil and turf properties resulted in variations of surface runoff percentages and total nitrogen (TN) concentrations in surface runoff and seepage. Because of the differences in the availability of washable TN, the A-3 soil (fine sand) resulted in lower TN losses than the A-2-4 soil (silty sand). The losses of TN were influenced by the intensity and slope of the rainfall, but the differences were significant (α=0.05) in only three of the eight cases analyzed. In the case of A-3 soils, the test series conducted during late fall resulted in higher TN losses than in the test series conducted during early fall season. These results suggest that the TN losses were lower where the soil allowed ready entry of the TN into soil, and in cases of less runoff. The fertilizer type did not result in a significant difference (α=0.05) in TN loss. The results of all test series and ANOVA suggest that the slow release fertilizers did not result in lower TN losses than the QR fertilizers. © 2013 American Society of Civil Engineers