Effect of Sodic Irrigation Water on Organic Carbon and Nitrogen Concentrations, Fluxes and Exports from Newly Installed St. Augustine Grass Sod in South-Central Texas

Population growth in towns and cities requires new construction of homes and conversion of native land use to urban and suburban landscapes. Municipal tap water is generally used for irrigating these urban and suburban landscapes and its water quality can differ globally dependent on whether it is sourced from ground or surface waters. We examined runoff dissolved organic carbon (DOC) and organic nitrogen (DON) concentrations, fluxes and exports from newly installed, fertilized and unfertilized St. Augustine (Stenotaphrum secundatum (Walt.) Kuntze ‘Raleigh’) sod irrigated with a sodic municipal tap water during two 5-week establishment periods (August and September). In unfertilized plots, concentrations of DOC in runoff significantly increased from 20.5 to 73.7 mg L-1 and from 29.6 to 113.3 mg L-1 Runoff concentrations of DOC in fertilized plots significantly increased from 27.3 to 72.0 mg L-1 and from 30.0 to 120.3 mg L-1. Concentrations of DON in runoff did not increase in either unfertilized or fertilized plots. Total DOC exports were 2036 ± 803 kg km-2 and 3341 ± 227 kg km-2 and DON exports were 99 ± 43 kg km-2 and 134 ± 15 kg km-2 respectively for the two turfgrass installation dates for the unfertilized plots. Fertilization had no significant effect on DOC and DON exports (p = 0.29 and 0.18). Na+, K+, Mg2+ and Ca2+ were implicated in both DOC and DON fluxes suggesting that as resources for irrigation water for urban landscapes decline and alternative irrigation water supplies such as grey and black water are utilized we would expect, due to their higher Na+ content that DOC and DON fluxes to urban watersheds will increase.