How to Minimize the Nitrogen Pollution Risk of Applying Reclaimed Sewage for Urban Turfgrass Irrigation

Abstract

Reclamation of treated sewage is an important way to alleviate urban water scarcity and optimize ecological layout, especially in irrigating urban turfgrass. Nevertheless, the irrational use of reclaimed sewage could result in risk of excessive nitrogen (N) pollution, which requires a scientific understanding and assessment. This study examined the water-N transport process of the turfgrass system with a HYDRUS-2D model that was accurately calibrated and validated using a set of field experimental data in North China. By integrating 15 scenarios with different irrigation levels and N applications into the model, the turfgrass water flow and N fate characteristics were estimated. The results showed that the adjusted HYDRUS-2D model effectively simulated the volumetric soil water content, drainage water, N leaching, and soil N residual. The temporal variation in turfgrass water loss and N leaching consistently followed that of precipitation and irrigation, with more than 60% of the total drainage water occurring from June to August. The N leaching was at its peak during April and August, and total ammonium-N and nitrate-N leaching was 2.86 and 2.02 kg/hm2, respectively. In simulated scenarios, the turfgrass drainage water was significantly reduced by 26.82% under I60%S1/3-I60%S3 scenarios (I was 100%, 80%, or 60% of total irrigation and S was 1/3, 1/2, 1, 2, or 3 times the experimental sewage concentration), while root water uptake only decreased by 0.85%. Meanwhile, N leaching and soil N residual were significantly reduced by 3.94% and 26.56% under I60%S1/2, respectively. Furthermore, by the TOPSIS entropy weight method, I60%S1/2 was identified as an optimal turfgrass irrigation strategy for the semi-arid region of North China. These results provide a guiding basis for sewage green treatment and urban sustainable irrigation on turfgrass.