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

Abstract

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.