Impacts of long-term reclaimed water irrigation on soil salinity accumulation in urban green land in Beijing

Irrigation with reclaimed water is becoming a common practice in many cities around the word. One of the main concerns regarding the use of reclaimed water in urban green land is soil salinity accumulation. Field investigations in the seven parks of Beijing were conducted to study the accumulation of soil salinity under different reclaimed water irrigation history. The accumulation trend and distribution pattern of soil salinity in a 100 cm soil profile were evaluated by the ENVIRO-GRO model. Field investigation results showed that average soil salinity in the plots irrigated with reclaimed water was higher than that irrigated with tap water by 19.2% at the depth of 0-20 cm. Difference of average soil salinities at the depth of 0-20 cm between field measurement and model simulation was quite small, less than 15.0%. Under irrigation water salinity of 0.6, 1.2, and 2.4 dS/m, simulated annually average soil salinity decreased/increased from initial value of 1.62 dS/m, to 1.53, 2.75, and 4.66 dS/m, respectively, at the equilibrium state. Accumulation of soil salinity in clay loam was 3 times of that in sandy loam. A mild to moderate soil salinization could appear under higher irrigation water salinity, lower irrigation water amount, and heavy soil texture. Irrigation practices and soil hydraulic properties were dominated factors affecting soil salt accumulation. It is not recommended to use water-saving irrigation and irrigate on heavy soils as well as plant with a salinity stress threshold less than 1.85 dS/m under reclaimed water irrigation in Beijing.