Urban Soils of Texas: Relating Irrigation Sodicity to Water-Extractable Carbon and Nutrients

Effective management of urban soils and their impact on surface water requires an understanding of the mechanisms controlling soil variability within and among cities. To gain a better understanding of soil variability among the cities of Texas, where the use of irrigation is common, we investigated the relationship between irrigation water chemistry and water-extractable soil dissolved organic C (DOC) and N (DON), NH4-N, NO3-N, and orthophosphate P in 33 irrigated soil samples under turfgrass from 26 cities. Quantified in a 1:10 soil/ distilled water extraction, DOC and nutrients were compared with the chemistry of the water used for irrigation (Na+ and Ca2+ concentrations, Na adsorption ratio [SAR], Na charge percentage [%Na(+)], alkalinity, and electrical conductivity) and several soil properties (silt+clay percentage, total soil C, and total soil N). Utilizing multiple regression analyses, SAR and total soil N explained 71% of the variability in extractable soil DOC, and SAR and alkalinity explained 72% of soil DON. The %Na (+) explained 43% of NH4-N variability and 56% of orthophosphate P variability observed among cities across Texas. Total soil N was the best predictor of water-extractable soil NO3-N (64%). Our results showed that when irrigation water SAR was > 5, there was a two- to threefold increase in the solubility of DOC and nutrients from urban soils of Texas, which may contributing to nonpoint sources of C and nutrients in surface waters.