Reuse of treated wastewater (TWW) for irrigation is one of the solutions to water shortage. Not only it saves water, it also supplies organic matter (OM) and other nutrients to the soil. However, long term application of TWW can affect soil physical and chemical properties. Additionally, substances added via TWW irrigation can accentuate already existent soil heterogeneity, which may impact physical and chemical processes in soils. As more agricultural fields are being irrigated with TWW, it is crucial to understand its implications on soils. The objectives of this research are to investigate: (a) the impact of TWW irrigation on soil heterogeneity, and on hydraulic processes; and (b) the fate of salts and nutrients in the subsurface in soils irrigated with TWW vs. tap water (TP). The experiment is carried out in Lachish farm, Israel. Two trenches were dug and a sensors network of 38 tensiometers, 37 TDRs, 6 redox probes, and 38 thermocouples was installed in high resolution in each cross section (1.5 x 1.5 m). The cross sections are 13 meters apart in a vineyard irrigated for over 10 years with TP and TWW. One cross section is in a TP area while the other is in TWW area. Soil samples were collected according to visually observed heterogeneity of the soil profiles and randomly. Chemical analyses were conducted in both soil and water samples. In addition, infiltration rate, Leaf Area Index (LAI), and harvest yield were determined. For irrigation water analyses, DOM in TWW is higher than TP (average concentrations of 25.9 and 1.4 mg/L, respectively). Soil organic matter is in average 1% higher in soils irrigated with TWW in the first 10 cm, while for lower depths OM content is the same under both treatments. No repellency was detected for either soils (WDPT< 5s), probably due to high clay content (>40%). ESP, EC and pH were higher for TWW soils, but not high enough to be characterized as saline and/or sodic. However, it presented SAR and EC levels of moderate infiltration reduction risk. Infiltration rate was lower in soils irrigated with TWW in respect to TP (1.05 and 5.46 cm/h, respectively). In addition, harvest yield was significantly higher in crop irrigated with TWW than TP (10.7 and 7.0 kg grapes/tree, respectively). Soil temperature was higher for TP profile, under same plant canopies (LAI = 2.1). For irrigated, dry and rainy seasons WC was higher in the TWW plot, reaching differences of up to 10% and higher retention capacity. In addition, WC varied considerably within the same depth in the TWW, reaching differences of up to 7% in the dry period, while TP station differences were up to 2%, which indicates increase in spatial heterogeneity. Overall, there were changes on physical characteristics of soils irrigated with TWW (higher retention capacity, lower temperature, lower infiltration rates) which had an impact on other processes. The research is still on-going, and the responsible mechanisms for the observed phenomena are still under exploration.
- 1875 HYDROLOGY Vadose zone
- 1895 HYDROLOGY Instruments and techniques: monitoring
- 1842 HYDROLOGY Irrigation
- 1865 HYDROLOGY Soils